Circular 106, Rum Manufacture, Rafael Arroyo, 1938

Follow along: IG @birectifier

Translated from Spanish by me. Please pay attention to Arroyo’s pragmatism and optimism. We are picking up right where he left off in 1949. We offer Arroyo’s beloved birectifier here.

Rum Manufacture

By Rafael Arroyo
Specialist in Industrial Fermentations. Chief, Chemistry Section of the
Agricultural Experimental Station of the University of Puerto Rico.

Three months ago we began the publication of a series of articles on the subject that heads these lines, coming out to the public in the important and well-known newspaper “El Mundo” of San Juan, PR. It was not then our intention to write this circular, which we planned to publish later, when we had finished the study that we have pending on rum manufacturing.

However, the public that gave us the honor of reading our articles, (and especially some of them dedicated to the exploitation of this important industry), showed such a warm welcome, and became so interested in the subject, that we began to receive letters from different parts of the Island asking us to collect the articles permanently. Pleasing our kind readers, we have decided to write this preliminary bulletin, which, with very small variations, represents the requested collection.

Far from our mind is writing as experts in the field, being an industry that, although ancient, has remained orphaned from serious and scientific study most of the time, as shown by the scarce, and mostly inaccessible literature on the matter. We do not pretend to play the role of mentors, we are as beginners at the most; but we do believe that we are in advantageous conditions to learn, experiment, observe, obtain data and draw conclusions.

Our consulting work has allowed us to appreciate the multitude of erroneous and ill-founded ideas that exist in the elaboration of this drink; and we have appreciated that there is much more skill in the rectification and preparation of commercial rum starting from the crude distillate, than in the production of this same distillate, or raw rum starting from molasses or cane juice as raw material. Especially we have found great deficiency in the appreciation of the fermentative process, where empirical practices and chance or luck factor still predominate in many cases.

Due to this state of affairs, we have given special emphasis to the fermentation process and those with it more related, trying to explain the importance of the selection of the fermenting agent and preparation of the raw material; how the process starts; methods of driving it; hazards to avoid, etc., etc., always keeping in mind the traditional and wasteful empiricism of the industry and channeling it to the efficient and economical methods of rational technique.

For better understanding we have decided to divide this work into a series of short sections that will include the following topics:

1. Importance of careful selection of the yeast.
2. Selection of raw material.
3. Pretreatment of the raw material.
4. Batición. [The mixture of yeast, substrate, nutrient, and water?]
5. Fermentation.
6. The distillation.
7. Healing of raw rum.
8. Chemical and biological supervision of the distillery.
9. What is the best equipment in a distillery?
10. Conclusion.


This factor is of inestimable importance for the distiller who wants a product of first quality, of invariable consistency, and with a seal of difficult distinction from cheap imitation. However, in most cases, the distiller rarely gives due importance to this factor, concentrating greater attention on the mechanical equipment of the business. Any yeast capable of producing alcohol through the fermentation of its batición is considered acceptable, as they have not thought about the great differences that may exist between different varieties.

For the few who, without profit for ideas, devote themselves to fermentative studies, with the sole purpose of investigating the existing possibilities of clarifying the technique or perfecting it, we can give an exact account of the mistakes made by distillers. Of these distillers there are many who are satisfied with the fermentation produced spontaneously by adventitious yeasts that almost always accompany the raw material, be it cane sugar or molasses. Others incorporate to the batición an indefinite amount of baker’s yeast, or any other that can be easily procured on the market. It is our object to highlight the danger of these practices, both from a technical and economic point of view.

It is to be expected that every rum manufacturer has conceived in his mind and carefully thought about the type of rum he desires, which must possess those qualities that make it appealing to the consuming public, while at the same time giving prestige to the production house.

Now, although there are many and varied factors that go into the making of a genuinely good rum, none has as much importance, or greater influence on the final success as the rum producing agent, that is, the yeast. Hence the importance of an adequate selection of the variety that we have to serve in daily work.

When selecting the yeast, the distiller must have two points well present:

1. Characteristics of the rum that you want to produce.
2. Equipment available for its manufacture.

When the yeast is chosen before the installation of the distillery (which is the most judicious and safe way) there is the advantage that the design of the distillery and its adequate equipment can be selected according to the needs and characteristics of the yeast, therefore subsequent success is more certain. Unfortunately, as a general rule, you leave the selection of the yeast (if it is ever done) for last, when the distillery is already built, equipped and ready to go into action. We believe here justified to give an explanation as to the convenience of selecting the yeast with priority to the installation of equipment or construction of buildings. We will cite two conditions that characterize the yeasts differentiating them from each other: optimum temperature of fermentation, and time spent in finishing. If we decide in our selection for a yeast that needs double time than another to finish the fermentation, it is obvious that we would need double the number of fermenters in one case than in another, with the subsequent larger space for the fermentation room, etc.

If the selected yeast is unable to withstand the high temperatures that usually predominate in the fermentation room, we must necessarily equip our fermenters with a refrigerating device, which could also bring changes in the overall design of the fermenter room. The yeast can also influence the construction and equipment of other distillery departments apparently disconnected directly from the fermentation process. For example, the building capacity of aging or curing of fresh rum, as well as the number of barrels to be used, can be modified by the characteristics of the fermentative organisms, since there is capability of producing a rum of fast, medium or slow maturity. Needless to say, the less storage time is needed to impart the necessary ripeness to raw rum, the lower the number of barrels used and the lower the cubic capacity of the aging warehouse. For these, and many other reasons, it is convenient to design the distillery once the characteristics of the organism that produces the rum are known.

On the contrary, given the case (which is the most frequent) that we already have the distillery equipped and ready to start operations, then it is equally important to select the most suitable yeast to the conditions of the factory. Although we repeat that the order must be inverse, that is, accommodate the distillery to the demands of the body that has to make the rum, and not the yeast to the restrictions of the distillery, because in this last case we would often be forced to leave to use the organism most adapted to the class or quality of the final product desired, due to equipment or space deficiency.

If, as we see, the selection of appropriate yeast is intimately related to the design and equipment of the distillery, this relationship increases and acquires greater importance when we consider it from the point of view of the finished product, that is, of commercial rum. Of course, we are considering especially the case where the distiller is also rectifier of the product; but even in the cases (as they exist) in which the distiller merely supplies the demand of the rectifiers with fresh rum, the selection of the yeast is always of great importance, since a rum that is bad when leaving the alembic, will NEVER be later a top-quality product, no matter how many rectification processes you pass through.

The most suitable yeast to use is that which, adapting to the existing factory equipment, is also capable of imparting the rum the desirable characteristics in a higher degree, while offering a reasonable yield. Within certain economic limits the yield is of less importance than the quality of the product. We must, therefore, determine, experimentally if possible, the type of rum we wish to produce, by means of the appropriate selection of fermentative organism. This can be a “heavy” type as Jamaican, or “light” as the Cuban, or something intermediate between these two we will extremes. The fundamental difference between the Cuban and Jamaican types is due 90 percent to the difference between the fermentative agents that come into play in the respective production, and perhaps 10 percent to the method of distilling and curing. From these points we will talk more extensively in subsequent chapters.

[Fermentation is everything! There is a fetish for the still, but new distillers need to get over that quickly and realize they are actually fermentation chemists. Arroyo argues that point constantly.]

The reader will ask: what are these differences between the diverse and varied strains of yeast that influence the rum so much? Well, the yeasts differ in the speed of propagation; in generation time; in the power of multiplication; in ability to attack different sugars; in resistance to contamination; in alcohol yield; in adaptation to different concentrations of sugars in the middle. They also require different concentrations of the hydrogen ion in the medium [pH]; different optimal temperatures; they produce different amounts of esters, aldehydes, higher alcohols, and other bodies that form the “bouquet” or typical aroma of rum; but above all they differ greatly in the ability to produce rum oil, which is, among all the aromatic bodies, the most important, and the one that prints a seal of exclusivity and distinction to the rums of high quality. On the nature of this rum oil we will talk more extensively in other chapters. From the above, we will see that the differences exist, and that therefore the careful selection of yeast is not mere theory, but a reality of importance, both industrial and economic.

[Rum oil is still not acknowledged by the industry which is still stuck on esters, sugaring, and age statement. Rum oil is the next leg up for rum and we have found it using the birectifier.]

Whatever the type or variety of yeast selected, it should be used only in pure culture; and what is of equal importance, the necessary measures must be taken to keep it pure during all the time of its use in the distillery. It is not possible to expect a product consistently of the same quality; invariable in taste, aroma, body, etc., if we do not use a pure culture, which prints its characteristics always in the same way and in the same intensity. Could we trust the stability of a building made of different mixtures and ignored proportions of the ingredients that make up the concrete? When working with adventitious yeasts or with impure cultures the distiller loses all sense of confidence and certainty in the final result, with each new batición that ferments, a new problem. It is also exposed to obtain very variable and always abnormal returns, without being able to trace the cause and apply the cure. As for quality, it will be more variable still and more uncertain than the yields.

Now, it is not enough to have a pure culture of any yeast to ensure good results; the fact of being pure does not always imply efficiency, nor does it guarantee that there will be a good rum, nor large quantities of it. It is necessary that the crop, besides being pure, be of an adaptable line to the production of rum; for example, there are yeasts capable of producing exquisite wines; but that applied to the manufacture of rum totally failed. There are also yeasts of unbeatable conditions for the production of industrial alcohol, but applied to the manufacture of rum are inadequate. The latter, although it seems strange is actually very natural and logical, since the qualities (except that of producing ethyl alcohol) that make a yeast recommended for the manufacture of industrial alcohol are antagonistic to the inherent qualities of a yeast especially adaptable to the rum production. In the first case, the ideal yeast would be one that transforms the sugars of the batición into ethyl alcohol and carbon dioxide only; while in the case of rum manufacture we have great need for secondary bodies such as organic acids; aldehydes, esters; higher alcohols; and above all, rum oil.

We have seen that we need to work not only with pure cultures, but that they must have the conditions and characteristics necessary to produce high quality rum. Satisfied these two conditions, the manufacturer must ensure to keep this culture pure and active. The latter is much more difficult than acquiring the culture. There are only two means of achieving this end, the first being indicated by the superior:

1. Using the services of an expert fermentologist, or bacteriologist specialized in this kind of work.
2. Installing a wide-layer pure culture machine
in the distillery.

Of these machines, we recommend the “Magñé” system because it is not the cheapest, but the easiest to handle, and those that best guarantee the activity, stability and purity of the culture.

Before closing this first chapter we wish to point out that in no way do we want to imply that the possession of a pure culture machine makes the presence of the fermentologist in the distillery unnecessary. Rather, we indicate it as an apparatus that reduces the risk to which the distiller is exposed, lacking adequate technical personnel, but never in the sense of making it unnecessary. On the other hand, in the case of distilleries of medium to large productive capacity, the machine is highly convenient, even if there is adequate technical staff.

[At this point in 1938 it should be noted that Arroyo has not mentioned Schizosaccharomyces pombe which is the yeast responsible for the heaviest rums. It was prominent in Arroyo’s later work.]

Selection of the Primary Material

This second chapter deals with an aspect of the industry that represents perhaps the one that receives the least attention from distillers, but which does not cease to be of great importance, both technical and economic.

We are fully aware of the fact that in the current conditions it is always difficult, and sometimes impossible for most distillers, to select the raw material. But even for the benefit of the few who are in an advantageous position to make this selection, we gladly offer them the product of our studies in that sense.

Generally, rum, at least on our island, is manufactured from cane juice, or final molasses from sugar mills. I have been able to observe, however, that the great majority of our rum comes from final molasses. Much is discussed about the relative advantages that each of these sources of raw material offers to the manufacturer, as well as which of them produces the best rum.

We will begin, then, by discussing the selection between one and another type of raw material, considering secondly the factors that should guide us in the selection within a same type.

The comparison and study will be done in relation to the following points:
1. Price of the material.
2. Performance in rum.
3. Ease of process.
4. Product quality.
5. Manufacturing price per unit of the product.

For comparative purposes we will choose representative final cane and molasses of average quality, respectively.

(1) Price of the Material.
One ton of cane obtains an approximate value of $5. With this sum of money you can buy 100 gallons of final molasses. In both cases what interests us for purposes of producing rum is the amount of total sugars acquired in exchange for our money. Although there are other factors of interest, these are not currently quoted when negotiating.

The ton of cane, when passed through a 75 percent extraction mill, would yield 1,500 pounds of juice containing about 17.5 percent of total sugars. We will have, then, that the ton of cane will give us (2,000 X 0.75 X 0.175) or 262.5 pounds of total sugars. The 100 gallons of final molasses will give us an average (known in practice) of 6 pounds of total sugars per gallon, or 600 pounds in the 100 gallons. There is no need to discuss the point more to see clearly in which of the two subjects it will be more profitable to invest our money, since we see by the numbers mentioned above that the final molasses for the same price must give us more than twice as much sugar as the cane . This, without taking into account the additional expense we have to make to convert cane into juice.

(2) Performance in Rum.
Exposed and demonstrated when discussing the relative prices of the sugar acquired when we referred to the price of the material, it is logical to suppose that we have to obtain more rum with the same capital investment in the case of using molasses. In effect, making the pertinent calculations in both cases we will find that the ton of cane will yield 33 to 35 gallons of rum at 100 P., while the 100 gallons of final molasses will yield 80 to 88 gallons of the product to the same degree . We clearly see the advantage of molasses in terms of performance

(3) Ease of Process.
We can anticipate that in this case also the superior molasses results, as we will demonstrate next.

From the point of view of initial equipment we find the need to grind the cane.

Already here we have the problem that the yield in juice will depend on the extractive power of the mill and the fibrous content of the cane. The amount of sugars extracted will also depend on the state of maturity and the variety of sugarcane. Other factors to be considered are the initial value of the grinding unit and its installation; cost of operation, personnel, repairs and spare parts; Losses of time due to mechanical accidents or lack of cane, etc. But it is not the mechanical inconveniences that complicate the process, but also biological disadvantages and complications, which deserve the attention of the distiller: The juice of the cane when leaving the mills carries with it a large part of the existing microbial flora on the bark of the cane, and on the earth and other materials that usually come with the cane to the mill. The mill itself, if not preserved in aseptic conditions, will serve as a source of infection for the juice extracted. Many of these organisms are able to produce undesirable fermentations in the medium and enter into strong struggle with the yeast producing the alcohol. The number of these organisms will fluctuate between 100,000 and several million per milliliter of juice. The consequences can be disastrous in the subsequent alcoholic fermentation if special measures are not taken.

Instead, the final molasses comes to our hands partially sterilized, due to the different heat treatments because it happens during the process of making sugar. It is true that it also contains micro-organisms similar to those found in juices, but in much less quantity. For example, the eminent bacteriologist and expert in industrial fermentations, Dr. William L. Owen, of Baton Rouge, La., in a microbiological counting of the products of a sugar mill, found an average of 280,000 micro-organisms of several species per milliliter of raw guarapo, while this figure was reduced to only 35,000 in the case of final molasses.

This data, and those already mentioned above, indicate that the process of making fresh cane juice rum is more complicated than cane molasses.

(4) Product Quality.

Many controversies and discussions have been heard among supporters of cane juice and those who prefer final molasses as raw material in the manufacture of rum. Although from the economic point of view the latter have managed to demonstrate the superiority of molasses over the guarapo, however their opponents, supporters of the guarapo, have never wanted to compromise on the quality of rum.

Respecting different opinions, ours is that under the conditions in which the industry is currently developing, and the manufacturing methods generally employed, it is more feasible to make a good rum of molasses than a mediocre one of cane juice. We admit, however, that introducing a special technique and the necessary modifications both in the pretreatment and in the fermentative process of the raw material, we could obtain a superior product of from cane juice over that of the molasses; but only as regards the elaboration of the so-called “light types” of rum, in the manufacture of “heavy types”, similar to that elaborated in Jamaica for export, we would always find the supremacy of the molasses over the guarapo. [The special technique may be the introduction of the Arroyo’s Oidium (which was actually an alt-yeast). If this is the case, though it is not spelled out, it means he worked with it for quite a few years before publishing Studies on Rum.]

(5) Manufacturing Price per Unit of the Distilled Product.

In the case of rum derived from cane juice, production must necessarily be more expensive, except in very special cases, details of which do not concern us.

In the first place we have the additional expense that represents the extraction of sugarcane juice, but even without this factor, we will see that when considering the cost of elaboration based on gallon of rum at 100 P. we will have in the case of using juices 15 cents for the initial value of the raw material, against around 6 cents for using molasses. It is customary to estimate the total processing expense per gallon of rum at 100 P. adding 3 cents to the cost of the raw material. Of course, there are variations in this figure from one distillery to the other, but in general it is an average amount accepted in good practice. Following this rule, we will have that the total value in the case of juice rum would be 15 + 3 = 18 cents; and in the case of molasses rum 6 + 3 = 9 cents.

From these calculations, it can be inferred that at first glance it will cost no less than twice as much to make rum from guarapo as rum from molasses. Actually the difference is even bigger, if we take into account extraordinary milling costs; mechanical difficulties, loss of time; and the greatest biological difficulties that arise during the fermentation of juices.

According to the discussions of the five topics that lead this article we have to reach the conclusion that under normal conditions, it is advisable to choose molasses as raw material. However, for those located in a position that makes them more favorable or convenient the use of cane juice, we would like to indicate that when selecting the cane, take good care in addressing the following points:

1. The cane should be as recently cut as possible.
2. Preferably use canes of “noble” varieties recognized as good sugar yields.
3. Choose varieties of easy grinding; that is, from low to fibrous.
4. The cane must be in full maturity.
5. The juice should be of pleasant natural aroma.
6. The rods should come to the mill in the greatest degree of cleanliness possible.
7. It should be used, preferably, cane from fertile land, or land extensively fertilized.
8. The juice of burned cane will never be used.

[A very cool list. Arroyo does not give up on fresh cane juice rum in Studies on Rum.]

Let’s see now how we should be guided in the selection of final molasses for use in distilleries. A careful and painstaking study carried out on the final molasses produced on the island with a view to determining their qualities for the production of rum, indicates that there is no great variation in the percentage of total sugars, expressed as inverted sugars, in the different molasses submitted to study. These molasses comprised representative samples of all the sugarcane districts of the Island, passing their total number of twenty. On the other hand, there were great differences in the contents of nitrogen, mineral matter (ashes), gums, and free titratable acidity. There were also notable variations in pH values, specific gravity, and natural aromas; as well as in the relationships between percent of sucrose (per Glerget) and inverted sugars; and between total sugars and ash.

Although the content of total sugars is naturally the predominant factor in the sale of molasses, there are others that greatly influence the performance and quality of the rum derived from them. Among these, we have the pH value in the first place; percentages of nitrogen, phosphorus, gums, and ash; and the inherent aroma of each molasses. This natural aroma of molasses can often be called bad; but good or bad, has to exert its influence on the resulting rum.

Like any other plant, the yeast needs nitrogen, phosphoric acid, potash, and other necessary elements to plant life. The molasses of our Island usually have in greater or lesser quantity these elements that have to serve as food to the yeast; but it does not always contain them in optimal concentration amounts. Potash is always present in large quantities; but we usually find deficiency in nitrogen, and less frequently deficiency in phosphoric acid. Instead, we often find abnormal amounts of ash and gums, which are adverse factors to a good fermentation.

The pH value of the molasses exerts great importance in the course of the fermentation because each micro-organism lives, grows, develops and multiplies better, under a certain optimum value of pH in the medium. The presence of high percentage of gums in molasses is detrimental to a good fermentation, since it exerts inhibitory functions in the yeast, reducing the yield and the quality of the alcoholic product. They usually give rise to an excessive percentage of higher alcohols in rum.

[I have never seen this spelled out like this. I’m not sure how a microbiologist would describe the inhibitory function.]

The specific gravity of the molasses must also be taken into account, preferring those of high specific gravity, that is, those of high grade Beaumé or Brix. In general, these molasses contain a greater amount of total sugars per gallon; and they are also less accessible to infections of undesirable organisms during their storage period. Low-density molasses has usually undergone a process of reheating and dilution in the sugar mills, to facilitate the work of the pump responsible for moving them from the well of the centrifuges to the storage tanks. This operation is usually carried out by the direct action of a jet of steam which, when condensed in contact with molasses, warms and dilutes it at the same time.

If this operation is unduly exaggerated, the resulting molasses will be of inferior quality for fermentative purposes, not only for the reasons already discussed above, but mainly because of the caramelisation that develops in it through the direct action of water vapor. Candy formation brings three fundamental evils:

1. Decrease the content of total sugars.
2. It develops a bad smell of an empyreumatic nature in molasses.
3. The caramel acts as an inhibitor of the activities of the yeast, weakening it greatly.

[I have never heard of this concept before.]

From here comes the importance we give to the determination of specific gravity and the natural aroma of molasses.

We still need to consider other factors of the internal composition of molasses that, although to a lesser degree, also influence the fermentation process, and consequently the quality of the rum resulting from it. Among these, we can mention the relation of sucrose to inverted sugars and that of total sugars to ash. While it is true that, as we said before, the percentage of total sugars does not vary much between molasses from different plants, there are large differences in the proportion of sucrose to inverted sugars. The latter can be found forming from a fifth to half of total sugars. Well, it has been shown experimentally that the most favorable ratio between sucrose and invert sugars for fermentative purposes is 2 to 1; that is, the total sugars should consist of two parts of sucrose and one of inverted sugars.

The ratio of total sugars to ashes is important because at the beginning of the fermentation the proportion of sugars to ashes is wide, for example 10: 1; but as the fermentation progresses this proportion narrows gradually, until in the end it is usually 1: 1. Now, this gradual increase in the concentration of mineral salts in the medium, hinders the physiological functions of the yeast greatly and therefore its fermentative activity. These difficulties are accentuated by the formation of alcohol in ascending scale and simultaneously with the increase in saline concentration of the medium. Hence, the broader the relationship between total sugars and ashes in molasses, the better quality it is.

[What Arroyo is describing is increasing osmotic pressure slowing down and then halting the yeast.]

To finish this second chapter we will recapitulate the factors that should be considered in the selection of a final molasses for use in distilleries. We will divide them into two categories: Primary and Secondary.

The primary ones include a knowledge of the content in: total sugars; nitrogen; phosphorus, ash, gums and pH value.

The secondary ones include the ratio of sucrose to inverted sugars and of total sugars to ash; specific gravity, and natural aroma of molasses.


With this expression we wish to signify that treatment to which it is convenient and beneficial to submit the raw material before entering the preparation of the batición. The process of preparing the batición will immediately follow this pretreatment, but that topic will be developed in Chapter No. IV.

The pretreatment process has two main objects:

1. Complete or partial sterilization of the medium.
2. The preparation of the medium in optimal conditions for the development, during the subsequent fermentation, of the aromatic principle known as “Rum Oil”.

We have already had occasion to mention this aromatic principle and we intend to deal more extensively with it at the opportune moment, given its transcendental importance in the formation of the “bouquet” or aroma of rum.

The first objective is achieved by applying heat at certain temperatures. The second, in addition to heat application, uses the action of an alkaline chemical agent; and in the distillery practice, we recommend the use of calcium hydroxide.

[plastering! or buffer cleaving! This was previously described in this supremely archaic paper from 1936 which Arroyo never references though he acknowledges his colleague translated a lot of German papers. Plastering was a brief fad in the history of Sherry production that was eventually outlawed because it had a laxitive effect from the potasium. Arroyo’s description to follow in 1938 is pretty succinct.]

The equipment necessary to perform the sterilization of the raw material differs in construction and initial cost, according to the kind of sterilization that we decide to produce; that is, absolute or complete; or the partial one. In case of using complete sterilization, a pressure equipment is necessary, consisting essentially of a cylindrical metallic tank, with facilities to be hermetically sealed and capable of withstanding water vapor pressures between twenty-five and thirty pounds above atmospheric.

The use of complete sterilization offers a single advantage, and many disadvantages, over the use of partial sterilization. The advantage consists of security and absolute confidence that the environment has been completely free of foreign microorganisms and harmful to our purpose, and that by taking the necessary precautions we can keep it sterile for an indefinite period of time. In certain fermentative processes, this absolute sterilization is of vital importance. The disadvantages are several, and diverse in character: first of all, the high temperatures to which we must necessarily submit to the environment can lead to undesirable changes in its physical or chemical structure, which invalidate it for the purposes we expect of it. Then we have the factor of high initial cost of the equipment and the necessary materials in their repairs; greater expense in the personnel that has to handle the equipment, because it must possess a certain degree of instruction and intelligence; and finally the risks of accidents, which are always latent in a pressure equipment.

Fortunately, the use of absolute sterilization of the medium is unnecessary and even undesirable (except in very rare exceptions) in rum distilleries, WITH AN EXCEPTION; and this is that the medium in which the pure yeast culture to be used as seed or foot in the fermenters must be absolutely sterilized before inoculation with the yeast in question.

Distilleries equipped with suitable pure culture machines have the facility to achieve this complete sterilization in the machine itself, therefore not needing any additional sterilization equipment. Among these, the pure culture machine of the “SISTEMA MAGNE” is designed to do this work in conditions of absolute safety and efficiency.

The case of partial sterilization of the medium is much simpler, less expensive, and is within the reach of any factory, large or small. It is not only feasible and desirable, but highly necessary. There is also the advantage in the case of partial sterilization of facilitating the combination of sterilization and treatment with calcium hydroxide in a single operation. The latter is important.

The equipment needed in this case consists of an iron or wood tank exposed to atmospheric pressure, and provided with a good Centigrade thermometer, heating and cooling elements, and an efficient mechanical agitator. This tank must be located at a level higher than that occupied by the tanks used in the preparation of batches, so that the material, once it has received its pretreatment, can freely discharge these tanks by gravity. We must also indicate that the pre-treatment tank must be of ample capacity, so that it can treat in a single operation all the raw material to be used in the batches during the day.

Let us now see how this pretreatment should be carried out in practice in the case where the raw material used is the final molasses: Due to the concentrated nature of the molasses in its natural state, although some dilution is needed, (consisting of a mixture in equal parts, BY WEIGHT, of molasses and water) still the pre-processor tank does not need to be of exaggerated dimensions. Its capacity will depend on the amount of daily molasses to be treated.

As an example, we will take a distillery that uses 1,000 gallons of molasses per working day. In this case, a pre-processor with a total capacity of around 2,700 gallons will be needed. In this tank 1,440 gallons of water will be poured and heating will begin. When the water has reached 80 degrees Centigrade of temperature, it will begin to incorporate the molasses, slowly, and keeping the agitator moving during the course of this operation. Once the molasses has been incorporated, the mixture will continue to be stirred for an additional fifteen minutes. After this time a sample of the mixture will be taken, to which, after having cooled it to the ambient temperature, a determination of its pH value will be made. This usually varies, but ordinarily it will be between 5.0 and 6.0. In all those cases in which this initial value is less than pH 5.8 and Beaumé 15-degrees, lime will be added to the mixture, cautiously, in small proportions; taking care to take the pH value of the mixture after each new addition of lime. When a sample thus taken turns out to have a pH value around 5.8 (it can vary more or less a tenth in value) the addition of lime will be suppressed. If during this time the temperature of the mixture has varied from 80 degrees Celsius, it will be brought back to this degree of heat, keeping it that way for an additional ten minutes. The mechanical agitator must be in action during all the time. After ten minutes, the operation is over, and then the cooling of the mixture will begin. It is not necessary to bring the temperature of 80 degrees to the ambient temperature, which would take a lot of time and expense of cooling. We must keep in mind that this material is still in concentrated form, that is, at a Brix around 44 degrees, and that to make the subsequent batición we will have to reduce it significantly with water. Therefore, the degrees of heat to which we must lower the pre-treatment mixture will depend in large part on the temperature of the water that we have to dilute the material finally when making the batición, and in the final degree of dilution that we desire for it. It is usually enough to lower the heat level in the pre-treatment tank to between 55 and 60 degrees Celsius. The addition of water necessary to prepare the batición will complete the cooling process.

In those cases in which the mixture turns out to have a pH greater than 5.8 before being treated, then enough slurry will be added to it to bring the pH value to 6.2; but once this process is finished, the mixture will be treated with enough diluted sulfuric acid to return the pH value 5.8 again.

[This establishes the pH buffer]

We have described this process in detail because of the great importance towards the quality of rum, and the risks that we would expose ourselves by not faithfully following the instructions to carry it out; because the treatment with calcium hydroxide, although simple in itself, is extremely delicate in its effects, and if it is not carried out with the proper precautions it can result in a bad, instead of a benefit, as we will explain later.

How has the raw material benefited through this double process of heating and lime treatment? Well in two different ways: (1) from the biological point and (2) from the chemical point of view.

By applying heat at 80 degrees Celsius during the indicated time, we have notably reduced the members of their bacterial colony, leaving in the material only the spores that are usually very resistant to heat. All vegetative form has been eliminated. The microbial life that could still remain in the medium will be in an inactive form, incapable of harming the subsequent action of the yeast, until it passes from the spore to the vegetative form. By that time the pure yeast seed will have taken full and predominant possession of the medium, neutralizing with its vigorous development and rapidity of action on it, any unfavorable action of these vegetative forms. In the case of yeasts of great rapidity of action, the alcoholic fermentation will be finished before the development of undesirable vegetative forms.

The purpose of the lime treatment is to make certain chemical changes in the composition of the medium, tending to prepare it so that the yeast can form, during the fermentation period, the most important aromatic principle of all rum, and the ONLY among all those that they form the “bouquet” that could not be imitated by chemical synthesis: we refer again to the so-called “Rum Oil”.

Having explained in detail the process of the pretreatment, and expressed its aims and importance, in the case of using final molasses as raw material, we wish to say something about the case in which the molasses is replaced by raw sugar cane.

The use of raw cane juice as raw material can be said to increase the need for the pretreatment process. First, as we have shown above, raw cane juice represents a material five to ten times higher in microbial contamination than molasses; and in the second place, it is more difficult to induce the yeast to develop the aromatic principle in guarapo batches than in molasses. We can assure that the development of this aromatic principle is little less than impossible in batches made with raw guarapo, even in the case of using the same yeast that would produce it in batches of pre-treated juice.

As for the pretreatment process, it is essentially the same as in the case of molasses. It differs only in details and in the case of the juice the treatment is carried out on a diluted material, which makes it (the treatment) much more expensive and complex. It would be necessary to use larger tanks and in larger numbers; it would take more space; more accessories such as stirrers, heating elements, thermometers, etc. Necessarily the calorie expenditure for heating will be much larger, and likewise the expense of refrigeration.

We must also warn that when the moment of adding the lime has arrived, it must be incorporated into the juice until the pH value reaches 7.0; This value is then lowered to 5.8 by the addition of dilute sulfuric acid. From this it can be deduced that the treatment of guarapo is more expensive than that of molasses in the cost of chemical reagents.

[These numbers reveal something missing from the rum literature and that is the size of the buffer that a heavy bodied ferment should run.]

All these factors that we are making known led us to say at the beginning that it was easier and much less expensive to make a good genuine rum of molasses than of guarapo.

Before closing this third chapter we wish to emphasize a warning that we already outlined when describing the pre-treatment process: While it is true that the treatment with milk of lime can be of great benefit to the raw material, it is also very true that this is an operation although simple, delicate. Therefore, this process must be directed by a competent and responsible person. If the alkalizing action is carried beyond the limits marked by the changes in pH value indicated in each case, the good could be turned into evil. This can be attributed to the release of organic bases or bodies of alkaloid nature, which will later appear in greater or lesser amounts mixed with the aromatic principle of rum. Those who have had the opportunity to smell these bases, separated from the fragrant constituents of rum, will surely take great care to avoid their generation during the pre-treatment process.

[First, do any producers currently lime their molasses? Secondly, would the process be practical for very small scale home distillers to perform as described here? And third, it is traditional as noted in the crazy 1936 document, but it is not something that Arroyo spends time with in his later work. What could the reason be? Was it made obsolete by other processes?

When we acknowledge these rare congeners that can be unlocked and the comparison between fresh canejuice, molasses becomes no waste product, but a concentrate of the aromatic divine, and sucrose becomes the byproduct. Sucrose does not sell for $100 a bottle. Rum and molasses needs new framing in its marketing arguements.

We can also re-examine the early Jamaican rum production. The ferments were known for high acidity but the pH may not have been as low as what we may have thought because it was buffered by the lime. Lime was accrued from the refining process but also in the various waste cisterns. If lime was just casually added to the waste cisterns, would it have released any evil alkaloid aromas that should have turned up in the literature?]

[This word has already appeared a few times. If you tried, this would translate to batter like cake batter. It is still used by the Spanish speaking industry and deserves to be used untranslated.]

The process of preparing the batición is the distiller’s last chance to impart to the raw material those conditions that will later facilitate the yeast to carry out its fermentation process under optimal conditions. The well-prepared batición is comparable to a land properly fertilized and conditioned for sowing; ready now, to receive the seed that will germinate in it, grow and produce the desired fruit. It is here, then, the moment to leave the batición in the most favorable conditions before passing to the fermenters to be inoculated with the seed or footing of pure yeast. What difficulties can this operation offer us? What factors should guide us in the preparation?

For the distiller who has previously made the study of their yeast, and the raw material used in the batición, this process will be extremely simple and safe. Knowing the natural limitations of its yeast and optimal conditions in which it is best used, as well as the deficiencies in the chemical composition of its raw material, the process of preparing the batición will be fast and safe, reducing itself to correct the deficiencies of the medium through the application adequate of the substances that lack, and on the other hand, to impart, with knowledge of cause, the physical conditions for the best physiological and fermentative development of the yeast.

If on the other hand (which often happens) the distiller is unaware of the characteristics of the yeast it uses, and the chemical composition of the medium on which it has to act, it is logical to assume that it may incur serious errors in the preparation of the batición. It necessarily lacks any sense of security and confidence as to what will happen at the start of the fermentation process, and for as long as it lasts. It will depend greatly on the LUCK or CASUALITY factor.

Among the errors that we can incur in this stage of rum manufacturing, are the following:

1. Inadequate dilution of the material.
2. Use of dilution water contraindicated for this use.
3. Improper adjustment of the pH value of the batición.
4. Use of inhibitory concentrations of total sugars.
5. Imbalance in the proper balance between nutrients for the yeast.

In our consulting work we had the opportunity to study a multitude of fermentative failures whose causes were easily traceable to the absolute ignorance of the yeast and the raw material used. Under these conditions, how could we ensure that the batición has been well prepared?

From what we have exposed above, the factors that come into play in the proper preparation of a batición can be inferred. In our opinion, the fundamentals are:

1. Accurate and thorough knowledge of the inherent characteristics of yeast that we will be used later during fermentation.
2. Equal intimate knowledge of the chemical composition of the raw material used.
3. The quality of the dilution water that used to prepare the batición.
4. Skill and experience of the person in charge of this work.
5. Existing facilities to maintain the highest degree of cleanliness in the equipment and its surroundings.

1. The knowledge of the inherent characteristics of the yeast has to help us a lot in the adequate preparation of the batición. Among other characteristics, we are concerned here greatly with the optimum pH that we must give to the medium and the optimum concentration of total sugars. We have already explained that yeasts differ in terms of the pH value of the medium that favors them to a greater degree, as well as the maximum and minimum values ​​that are able to resist without losing their fermentative vigor. Therefore, when making the batición, we must give it that pH value that represents optimal conditions for our particular lineage. Our experiments in this regard tend to indicate that the great majority of rum yeasts prefer a pH of 5.8 for the production of the best quality and yield of rum. On the other hand, the yeasts for the manufacture of industrial alcohol seem to prefer a pH of around 5.0 for their better development. We could not, however, mark this value of 5.8 pH as standard and invariable in all cases; On the contrary, we recommend that each distiller take the trouble to determine the optimum pH value in which his yeast is used.

With the use of a potentiometer or pH device, it is easy to adjust the desired value in the batición. This adjustment is made by the addition of alkali or acid, according to the initial pH value of the batición. Subsequent readings of the potentiometer after each addition of the appropriate reagent, will reveal the moment in which we have reached the desired concentration of the hydrogen ion.

[pH was a fairly new concept at this time.]


[If we set up an array of options, this would be a good guide to picking the optimal. Studies on Rum in particular is important for teaching the progressive process which develops productions from scratch.]

As for the adjustment of the concentration of total sugars in the batición, we could say that it is as important or more important than the adjustment of the pH. This and also the knowledge of the characteristics of the yeast used can guide us very accurately. There are yeasts that can ferment concentrated solutions of sugars (within certain limits, it is understood), while others are only capable of fermenting solutions of comparative low concentration. Between these two limits, there is a whole scale of concentrations favorable to certain strains and unfavorable to others. Therefore, nothing would be gained by increasing the density of the batición with the idea of obtaining more alcohol in the same volume, if our yeast is unable to resist those high concentrations.

We have had the opportunity to analyze already fermented batches, in which we have obtained values of residual sugars between two and four percent. This shows that the yeast used fermented a very concentrated batición for its means, leaving without attacking too high a percentage of the sugar content. The normal values for residual sugars are between 0.5 and 1.5 percent. We see, then, the importance of knowing in depth the characteristics of the yeast, and with this knowledge as a base, prepare the batición in optimal conditions of pH and concentration of sugars.

[So if we capture a yeast and start from no knowledge, we should start from small gallon array, varying only pH to find the optimal and then total sugars to find our ceiling. This would be part of the yeast olympiad performed to find rum champions.]

For the exact determination of the concentration of total sugars in the batición, it is necessary to make a direct determination of them by chemical or physical methods. From these methods we will give details in section No. VIII, when discussing the chemical and biological supervision of the distillery.

In practice, distillers devoid of chemical laboratories and technical personnel, (who are the most) are guided by the degree Brix or Beaumé of the batición. Although this practice offers inaccurate guidance, it is always beneficial in the absence of better methods. Our experience indicates that in the case of rum batches, the optimal value is almost always between 15 and 18 Brix degrees, corresponding in the Beaumé scale to 8.34 and 10.0, respectively. But as we said before, these values obtained by using the hydrometers Brix, or Beaumé; they are not exact to calculate the content of total sugars in the batición, since those values only indicate the content of total solids in solution, among which enter many other substances besides the sugars. Generally the reading of 15 Brix in case of a batición of final molasses indicates 10 to 10.5 grams of total sugars per 100 milliliters of batición.

2. The intimate knowledge of the constitution of the raw material will greatly facilitate, of course, the preparation of the batición. We have already explained that in addition to sugars, yeast needs other substances for its subsistence, propagation and development. We also said that these substances must be in adequate proportions. It is therefore of great interest to the distiller, to be sure that their batición will be done in accordance with the conditions stated above, that is, that they must not lack, in the proper quantity, any of the substances necessary to the yeast.

Among the elements that are most needed are the yeast: carbon, nitrogen, phosphorus and potassium; Iron, sulfur, manganese, magnesium and calcium come later as less important.

The carbon is used as energy, formation of glycogen, hemicellulose, proteins, yeast gum, etc., nitrogen mainly for the manufacture of proteins and enzymes; Phosphorus, besides being physiologically essential to yeast, plays an important role during fermentation. Without the presence of phosphorus the formation of alcohol is not possible. The other elements are also important, although to a lesser degree.

Fortunately, both molasses and cane sugar contain in variable quantities most of these elements; but there are cases of deficiencies, especially in nitrogen and phosphorus; and these deficiencies must be corrected when preparing the batición. However, in doing so, we must be careful not to increase the nitrogen and phosphorus content more than necessary, since besides the initial cost of these ingredients, which would increase the cost of production, we would have a greater disadvantage still, namely that when the yeast is in an excessively rich medium in these elements, the phenomenon of “fermentative apathy” is produced, in exchange for an extremely vigorous multiplication and cellular development, in the vulgar language we would explain this phenomenon saying that the yeast becomes lazy for the production of alcohol.

It is necessary to preserve above all the optimum balance in the balance between total sugars and the elements of a nutritive nature, thus stimulating the yeast to the maximum of alcoholic production.

3. The quality of the water used in the dilution of the raw material when preparing the batición is of great importance, especially if we have used the pretreatment process already described. The quality of the dilution water will influence not only the course of the subsequent fermentation, but also the distillation process to which the already fermented batición must be subjected. Of how the water used in the batición affects the distillation process, we will talk about it when we get to the chapter that deals with the process in question. Therefore, we will briefly comment on how it affects the fermentation process.

The use of inadequate water, especially in its bacteriological aspect could spoil the work done during the pretreatment of the raw material. The dilution water could be of such poor quality that its microbial contamination exceeds that which originally brought the raw material before its pretreatment. If so, what would we have gained, from the point of view of partial sterilization, with the pre-treatment, if the work then carried out would have been spoiled during the preparation of the batición?

It is therefore necessary to use the purest water possible from the microbiological point of view, and reasonably pure from the chemical point of view. If it were not possible to find natural waters of these conditions, the installation of a water treatment and filtering plant is imposed on the distillery. We have seen cases in which the alcohol yield has been reduced to less than half, due to the poor quality of the water used to make the batición. This will give an idea of the enormous importance of the water quality in the distillery.

4. When it is desired to prepare properly the batición, it is necessary to begin by choosing a competent personnel to carry out the operation. The manager of this department must have at least certain notions of what a change in pH value means; what importance it plays in fermentation that the batición has received the proper dilution; that contains the proper concentration of total sugars; the necessary nutritious foods, etc. It must also be instilled from the beginning to the staff, the need that exists to work at all times within the strictest conditions of cleanliness. It represents a very costly economy to leave such important work in the hands of someone irresponsible, for the mere fact of being able to settle for a few pesetas less than a day’s wage.

5. The tanks to prepare baticións must be of copper or polished steel; of cylindrical shape, and equipped with mechanical agitator or compressed STERILE air system. We prefer the agitator due to the difficulties inherent to the conservation of the air in a sterile state. There must also be facilities for cleaning it. The use of “steam broom”, similar to the one used in the vats of the sugar mills every time a tempered batch is discharged, would be highly recommended here.

As much as possible in each case, it is necessary to keep these tanks and their surroundings in absolute cleanliness. At the end of the day’s operations, the tank or batición tanks should be washed with a “steam broom” or hot water. After this treatment it is very convenient to treat an indoor and outdoor bath with a solution of “Montanin” or “Antiformin” at 5 percent. When they resume their use the next day they will be washed again with hot water.


We have reached the climax in the manufacture of rum. The fermentation process will largely decide the fate of the finished product. All that we have previously exposed, all the care in the selection of yeast and raw material, as well as the operations described during the stages of pretreatment and preparation of the batición, have been carried out with the sole purpose of ensuring the success of the fermentation process. At the end of this very important stage of the process, we have to find in the fermented material all the ingredients of a raw rum of the highest quality. In the fermented liquid is the desired product; we will only need to take the necessary care to separate it with skill from all those elements that could harm quality.

[This is wildly important. Fermentation is the climax, not distillation. We need fermentation fetishes, not distillation fetishes.]

This process by which we extract the volatile elements that make up a good raw rum from the fermented batición, will be discussed in a timely manner. For now let’s consider the fermentation process again.

In the previous chapter we described how to prepare the batición, and the influence that an adequate preparation of it has about the fermentation process.

Some distilleries prepare their baticións in the fermenters. This practice is not recommended, but there must be special tanks for that purpose. In these special tanks (which we have already described) we will have the opportunity to prepare the baticións, correct defects, and leave them in the most favorable conditions before being transferred to the fermenters. The main reason we have to proceed in this way is that, in this case, we are free to incorporate the batición to the yeast footing, which we will have in the fermenter; whereas if we prepare the batición in the fermentor, we would necessarily have to incorporate the yeast footing to the batición.

[This sadly will have annoying logistics at the scale of one barrel per day and where people like to ferment in old molasses totes.]

Some of those who do us the honor of reading these lines will ask themselves— what else is there to incorporating the yeast footing into the batición or vice-versa? In appearance it seems indifferent to follow one or the other course; but in fact it is much more convenient and offers more guarantee of fermentative success to incorporate the batición to the yeast footing. We will explain why:

It is known that the initiation, and consecutive development of fermentation are directly influenced by the number of active cells in unit volume. To illustrate this fundamental principle, we will give an experiment carried out to this effect: Five 100-milliliter portions of a final molasses batición, containing 5 grams of total sugars each, were inoculated with different amounts of the same yeast in pure culture; then measuring the time required in each case to complete the fermentation. The results obtained in tabular form follow:

Grams of yeast in 100 ml. of batición versus number of hours at 30°C to complete fermentation:
8—————————————————————————- 10
4—————————————————————————- 20
1—————————————————————————- 92
0.5————————————————————————- 180

The results of this simple experiment clearly and conclusively prove the effect of yeast cell concentration per unit volume of batición. Now, if we have the yeast footing in the fermentor, and fill it with the batición, the cell concentration will be slowly diluted, since it will take one or several hours to transfer the batición to the fermenter. In addition, the number of cells originally contained in the footing will be reproduced as the fermenter is filled to its mark, so that at all times we will keep the medium in active fermentation. Another advantage of this method of inoculation is the possibility of using less footing volume if necessary. Also the mixture of the footing and the batición is much more efficient and effective. If on the other hand we follow the method of incorporating the yeast footing to the total of the batición, we will have a great and sudden dilution of the cellular concentration, which, as we have seen, retards the fermentation, and in exaggerated cases it can prevent it from completion. Therefore, those distillers who, due to the nature of their equipment, are forced to make the batches in the fermentation tanks, and then incorporate the yeast footing into them, must take special care with the volume they are to use. In these cases the volume of the footing will vary with the vigor and propagative speed of the strain of yeast used; but in no case should be less than 5 percent of the total volume of the batición, and we would recommend a 10 percent for greater safety.

[This last bit of advice, may apply to new very small American producers, but what we are missing is yeast cell count data. How concentrated is that footing? Even in 1938, I think they had specialty microscope slides for counting cells. Now we even have affordable automated counters.]

With the incorporation of the yeast footing to the batición or vice-versa, the fermentation process is started. Now, in either of the two methods, the seed or footing must be prepared, and in conditions of vigorous development as soon as the batición is ready to be fermented. The batición should NEVER have to wait for the footing, but it must always be ready and in conditions of maximum cellular concentration. When the batición has to wait for the seed, we expose ourselves unnecessarily to harmful contamination; especially when we work with open equipment, in continuous exposure to the air. On the other hand, this delay is always time lost in the production of rum. What to do, then, to have a footing always active and vigorous, ready at any moment to take action? The use of a pure yeast culture machine is the best guarantee that the distiller has to avoid costly delays, and possible contaminations that tend to be more expensive still.

[I would be great to link to a detailed explanation of the vigor concept and I remember a great one in one of the modern distilling texts. I will have to track it down.]

Especially suitable for these purposes of conservation of the culture is the pure cultivating machine “Sistema Magné”. In these machines the yeast multiplies very quickly due to the facilities it offers against contamination, and the admission of air under sterile conditions, which provides ample oxygen to the yeast culture that encloses its development and procreation chamber.

Whatever the mechanism used to procure the yeast footing, this, as we said, must always be ready to be used. The development time of maximum cellular concentration of the footing should be measured in such a way that the batición never has to wait for the footing. The union of yeast footing and the batición must come in the cycle of maximum cellular concentration, and of maximum activity and vigor.

We have discussed with some largeness the matter of the preparation, quantity, mode of incorporation, and other properties inherent to the yeast footing, because this seems to us the predominant factor of the fermentative process. All the precautions taken during the pretreatment of the raw material and compounding of the batición would be null in their ends if we did not possess a pure yeast seed and in vigorous activity, to begin the process of the fermentation.

After the fermentation started by the combination of the batición and the yeast footing, we could not give fixed rules to follow until the completion of the process, since everything depends on equipment conditions; facilities for mastering the different factors that influence during the duration of the process; inherent characteristics of the ferment used; qualities that we wish to impart to the final product, and chemical and biological supervision existing in each case. The differences existing with respect to the conditions listed above will cause the fermentative methods to vary in one or the other distilleries. We will limit ourselves, then, to citing points of general application, although flexible to the variations that each distiller would like or needed to give them.

One of the factors of the fermentation that is very interesting to the distiller is the total time that this process will take. In the first place this time lapse is governed by the characteristics of the yeast. There are some that are very active, capable of finishing the fermentation in 24 hours or less. Others have to require two or three days under the same conditions; and still others, that it would take seven to ten days to complete the work. Hence the importance of choosing carefully the yeast most appropriate to our conditions.

Now, the distiller has certain means of modifying the fermentative time to a certain extent, regardless of the kind of yeast he uses. This modification can be of an accelerating or retarding nature, as desired. To accelerate the fermentation we will begin by using a yeast footing of greater proportions than usual. For example, one of our experimental yeasts takes up to 72 hours to finish when the batición is inoculated with a footing equivalent to 5 percent of the total volume; from 48 to 56 hours, if the footing volume goes up to 10 percent; and at 36 or 40 hours if we use a foot of 15 percent of the total volume of the batición. We have, then, that one of the easiest means at our disposal to accelerate the fermentation is to increase the amount of yeast footing used. Another means is to incorporate the batición to the footing and not vice-versa, as we have already discussed. The combination of both factors is, of course, even more effective. We can also accelerate the fermentation by increasing the temperature at which it takes place. This latter method is more feasible in temperate countries or in tropical distilleries located at appreciable height above sea level; because generally in the tropics the temperature of the fermenters is such, that rather it is necessary to look for, means of reducing it.

The optimum temperature of the best yeast breeds for rum production is between 30 and 35 degrees Celsius. After these values the fermentative power and cell multiplication diminishes considerably, losing completely around 50 degrees Celsius. Therefore, keeping the temperature of the fermenters between 30 and 35 degrees will accelerate the fermentation.

We still have three other means, different from those already mentioned to accelerate the fermentation. One of them is the use of large capacity fermenters. Contrary to appearances, small fermenters take longer than large ones to complete fermentation. This is due to the relationship between cubic capacity and tank surface on the one hand, and on the other, because in large volume fermenters the internal temperature is affected to a lesser degree by changes in the external environment. In other words, the temperature remains more constant. Another means is to use low concentrations of total sugars when making the batición. The batición with low concentration of sugars offer less work to the ferment, and also the concentration in ascending scale of the alcohol that is formed as the sugars are used, never reaches the inhibitory degrees for the yeast. Finally, we can accelerate the fermentation by means of a gentle mechanical agitation of the medium, supplemented with the addition of certain activating substances, such as very fine charcoal powder, sterile bagasse, infusory earth, etc.

[These last two substances are in the literature as methods of restarting stuck fermentations. Somehow, having a physical site for yeast to stick to effects them positively and even changes their reproduction. I’ve seen in the cachaça literature also the use of corncobs and lemon rinds added for the growth of yeast starters at the beginning of the season. Lemon rinds may have been used also because citric acid changes yeast metabolism. We know that citric acid is a big negative for rum fermentation, but it may have benefits for creating yeast footings.]

Of all these means that we have mentioned, we recommend the one related to the volume and method of using the yeast footing when inoculating the batición as the one of easiest manipulations, and the one that offers the best results.

If, on the other hand, we wish for slower fermentations, we will do the opposite of what was stated in the case of acceleration. That is, we will use the smallest footing compatible with a good fermentation; we will lower the fermentation temperature; we will raise the concentration of sugars by making the batición as far as is feasible without interfering with the economy of the process; we will eliminate the use of activators, etc.

Which of the two fermentative methods is the best to use, the fast or the slow?

This question can be answered according to the kind of rum that we want to produce and the equipment comforts that we have. If we want a product with a lot of body, high content of esters and other aromatic bodies; and above all, the presence of rum oil, then we will answer that slow fermentation is preferable. In this case, in addition to the use of a slow fermentation yeast, it would be necessary for the equipment to adapt to the characteristics of the yeast. For example, by using a yeast of this kind, or by delaying fermentation by the aforementioned methods, the distiller is at greater risk of infection of the medium during the fermentation process if it lacks the equipment prepared expressly for such fermentations. First, pretreatment, which is always desirable, then becomes a necessity; and in extreme cases it would be necessary to resort to the practice of absolute sterilization of the environment. In addition we would need ample capacity of fermentors, and these of the closed type. In two words, our concern would be the protection of yeast against possible infections during the long fermentation period.

[Notice, Arroyo does not mention aroma-beneficial bacteria yet.]

If, on the other hand, we want a rum with a low content of esters, little body, and a low general concentration of the congeners of alcoholic fermentation, then the more quickly the fermentation process ends, the closer we get to the desired ideal. Rapid fermentation offers the advantages of being able to perform with less expensive equipment and processes, less expert personnel, and with greater guarantee against possible unwanted contamination. But the distiller must have as a fundamental basis of his business, the Quality of Rum. Nothing should be done that tends to diminish this quality, which in the end, is the factor that determines the success or failure of the company. Therefore, the fermentative method to follow must be the one that assures us the best product, although it involves more care and manufacturing expenses. Price-based competition is only fleeting, and it is counterproductive sooner or later. It is only lasting and sustainable competition based on quality and service.

How will the distiller know if its fermentation is progressing favorably?

There are several methods to follow the progress of an alcoholic fermentation. The most scientific and safe is to take samples at intervals, agreed to by the fermenters, and determine the percentage of total sugars and alcohol in them. But to carry out this work we would need laboratory equipment, reagents, and technical personnel. The simplest method is to take note of the attenuations suffered by the fermenting liquid at certain intervals, for example every 6 or 12 hours; according to the fermentation class under study. The distiller will note the Brix degree of the batición at the time of inoculation. If the yeast is fast acting, this reading will be taken in periods of 6 hours until the end of the process. If the yeast acts slowly these periods of time will be extended to 12 or 24 hours, according to its greater or less fermentative activity. It will be observed that the Brix hydrometer will indicate readings in descending scale until being parked in one of them. When two consecutive readings indicate the same Brix degree, we can infer that the fermentation has ended. The lack of movement in the liquid produced by the carbon dioxide generated simultaneously with the formation of alcohol, is another corroborating indication to the reading of the Brix hydrometer.

However, not always has the fermentation been carried out completely and satisfactorily because we obtain the signals indicated above. It can stop the fermentation prematurely, leaving in the liquid considerable amount of sugars without turning into alcohol. The causes are several; exhaustion of the elements that serve as nutrition to the yeast; weakness in the fermentative power of the yeast due to the inhibitory effects of other organisms that have gained access to the fermentor; elevation of the temperature to inhibitory degrees for the ferment; alteration of pH by the products of foreign organisms, etc.

But the distiller who knows its yeast knows, of course, the total attenuation that it is capable of, and the reading of the Brix hydrometer will indicate whether or not it has reached the point of usual attenuation. If, despite not reaching this point, the appearances of the batición indicate that the fermentation has ceased, then it is necessary to investigate the cause, or causes of the phenomenon and apply the necessary corrective. Distilleries that exercise adequate chemical and biological supervision are rarely confronted with these cases and if one emerges, the cause would soon be found and the remedy applied.

There is another rarer fermentative phenomenon: The liquid in the fermenter is apparently in vigorous action; but the Brix hydrometer readings do not descend as usual, barely indicating attenuation. These cases are almost always caused by the presence of certain bacteria capable of continuing with the fermentation of the liquid once the yeast is inhibited; but without producing the corresponding alcohol formation. As these organisms generally produce organic acids and other chemical substances that have approximately the same specific gravity of water, the Brix hydrometer can not mark the attenuations with the great differences that the formation of alcohol produces in the medium. Hence the importance of chemical and biological monitoring of a distillery. It is when things go wrong, that the presence of the technician becomes so desirable.

When should the fermented material pass to the distillation process?

As a general and fixed rule we wish to state that in any case the fermentation must have come to an end. When we distill the contents of a fermenter without waiting for the fermentation to be completely finished, we will first obtain a reduction in the alcohol yield, and secondly, the quality of the product will suffer as well. We will notice an excessive rawness and lack of ‘bouquet’ in the distillate. There is a practice among some distillers of letting the material stand for 24 to 36 hours after the fermentation is completely finished, before distilling it. This procedure is highly recommended from the point of view of the good qualities of softness, taste and “bouquet” that is imparted to the distillate when the resting treatment can be done in favorable conditions. To follow this practice we need, of course, a good number of fermenters, preferably of the closed type; or have closed tanks, specially constructed for this purpose. Once the fermentation is finished, the contents of the fermenters are passed to these special resting tanks, which would be the best method, as this would leave the fermenters free for their cleaning and new use.

The objections to the practice of resting are that if the fermented material is allowed to stand in tanks exposed to air, we would have alcohol losses through evaporation, and what is worse, the danger of contracting contaminations of microorganisms prevailing in the environment, especially attacks of Mycoderma aceti, which are common in the distillery.

[One thing that may also be lost is excessive low boiling point low molecular weight congeners that are in excess and need cut away. Robert Léauté mentions that Cognacs are even fermented at a certain elevated temperature to blow off some of these excessive congeners.]

Our experiments have made us widely know the advantages of the process of resting the fermented material before submitting it to distillation, and we wish to end this chapter by declaring that we are determined supporters of the process, provided that the distillery has the right equipment and personnel to practice it.


In a general sense, the distillation consists in separating more or less completely a volatile liquid of fixed substances, or of less volatility, to which it is associated.

The fermented batición contains solid substances decanted and suspended in the liquid; soluble fixed substances (organic and inorganic salts, fixed organic acids, etc.); a whole series of volatile liquids; and gases, especially carbon dioxide, dissolved in the medium. Although the composition of the fermented liquid is very complex, it is essentially formed primarily by water and ethyl alcohol. The numerous other bodies that accompany water and alcohol vary in the degree of volatility, some being less, and others more volatile than alcohol. There are these in very small proportions, very small in some cases, but in rum manufacture they are not in any way unimportant, since they will make the distillate of their body, flavor, and peculiar aroma of rum.

Among the volatile substances that concern us, besides alcohol, we have a whole series of organic acids: acetic, propionic, butyric, caprylic, capric, laurelic, and others; being between these of greater importance regarding the respective amounts present in the mixture, acetic, propionic and butyric acids. We also have aldehydes, especially acetaldehyde; higher alcohols such as propanol, butanol, pentanol and others higher in the series. Finally, we have esters, which result from the chemical combination of acids with alcohols, essential oils of various kinds, glycerin, and in some cases very variable but always small amounts of rum oil which is perhaps the most important, in terms of the formation of the “bouquet.” The rums that possess it to a greater degree obtain a seal of distinction in their aroma that gives them an individuality difficult to match or imitate.

Applied to rum, the distillation will then have as its object the isolation of the fixed substances and most of the water, the ethyl alcohol and those of its volatile congeners whose condensed vapors will constitute the distillate or raw rum.

Which distillation device will be the best to use? This question has been formulated to us in different occasions, and in fact it is of difficult answer without before making a complete analysis of the inherent and peculiar conditions to each case. We will say, however, that there are at least three methods that can be used in the separation of raw rum from the mixture that represents the fermented batición:

1. By successive simple distillations, or what is the same, using the rectification method by means of redistillation. Any distillation device, no matter how simple its construction, lends itself to this case.
2. By using an batch or discontinuous distillation still.
3. Through the use of a continuous distillation still, which are the most used in the native industry.

Due to the inexpensive nature of the first method, in terms of the time spent and the expense of fuel necessary to make three or more successive distillations, it is almost completely eliminated in practice. We mention it, however, because it is the one that produces the best quality raw rum. We have repeatedly compared distilled rums of the SAME BATICIÓN; but using the three methods outlined above, and in all cases the crude rums made by redistillation resulted in superior products. Nothing is strange in this, if we consider that the best Cognac in France is distilled in this way. And what is the cognac but a rum of fermented and distilled grape juice? In those cases in which the fuel is free (for example, using the excess of bagasse produced by some plants), or very cheap, and also does not have to be produced on a large scale, this distillation method is highly recommended.

The second method, although not as widespread in Puerto Rico as the third one, is a commercial method of great benefits and in Jamaica and the French Antilles it is the preferred method to distill the rums that obtain the highest price in the world market. This second method, that which uses stills of batch or discontinuous distillation, offers certain advantages and disadvantages; advantages in terms of product quality, simplicity of construction and flexibility in operation; and disadvantages in terms of production limitation per unit, time and fuel economy. With modern stills of this type, however, the disadvantage caused by loss of time during the loading and unloading of the fermented batición vessel, is almost eliminated, as there are those that are constructed with twin containers, attached to the same column, so that while one is distilling, the other unloads its exhausted batición, and cleans and recharges with new batición to recommence the distillation as soon as the one that is being carried out is finished. In this way the distillation is almost continuous, and we would only have the disadvantage of higher fuel costs.

The third method of separation of raw rum, that is, the one that uses a continuous distillation still has, as the first mentioned, its advantages and disadvantages. The main advantages are economic: higher production per distillation unit, more compact system and considerable savings in time and fuel. On the other hand, the great majority of the stills of this type built up to the present, although admirably designed and without rivals for the production of industrial alcohol, does not happen the same when we apply them to the production of rum and especially of HIGH QUALITY rum. The main reason is that in these devices there is no degree of fractionation necessary to separate the bodies of good and bad taste, which pass mixed in the distillate. It follows that the distillate will contain more or less what we call undesirable bodies. When it comes to eliminating this objection, it usually falls into the inverse excess; that is, the distillate will be so pure when it leaves the final condenser, that it stops being rum (although legally it bears this title) to become low-grade commercial alcohol. Put in simpler words, the case of the distillation of rum in stills of continuous distillation offers the disadvantage of not being able to produce rum at low grade (between 130-140 P.) without excessive drag of impurities and to eliminate this inconvenience we are obliged to distill to such high alcoholic degrees (170-180 P.) that then not only we eliminate the “undesirable ones”, but also the indispensable bodies to the constitution of a good rum.

Know this principle, manufacturers of stills for continuous distillation for rum, have been striving to build devices that ensure the continuity and economy of the continuous type with judicious fractionation of products, which offers the batch type. In some cases a quite happy solution to this problem has been reached.

Regardless of the type of equipment used, the fermentation process and the composition of the fermented material will greatly influence the distillation process. All the different types of materials contained in the fermentation (which have been previously mentioned), influence, or can influence the distillation process, according to the treatment suffered during the fermentation process and the more or less effective measures we have to eliminate any adverse influence on the production of a good raw rum.

Distillers that are accustomed and are properly prepared to give rest to the fermented material indirectly benefit the distillation process, because during this time of rest the suspended materials will have the opportunity to decant, going to form part of the material already deposited in the bottom of the tank. Both the suspended and the sedimented material have the same composition, approximately, being formed in their great majority of yeast cells and part of the non-sugar components of the raw material, which have been precipitated due to the increasing acid reaction of the medium and to the alcohol that has been forming. In its great majority with organic nitrogenous substances.

Now, as far as the distillation is concerned, it is highly important that this suspended and decanted material be removed such a fermented liquid before it enters the still. Why? Well simply to avoid the formation of undesirable odors that jointly define “TUFO”. [tufo means “stink”]

And since we have mentioned it, we will allow ourselves not to go forward without saying two words about this so-called “tufo” of raw rum. This should not exist in a well fermented and better distilled raw rum. Our experiments have also shown that by taking the precautions of rigor, it is not necessary to distill to 170 or 180 P. To eliminate it. We have distilled rums from 120 to 160 P. Without that in a single case it could be noticed in the distillate the characteristic smell of “tufo”?

[It is hard to say if this is related to acrolein, well explained by Fahrasmane and responsible for “peppered” whiskies or is just a product of yeast autolysis. These products end up collected in the last three fractions of the birectifier. If they are present in a pre-screening process, the spirit could be distilled slightly higher and a different cutting regimen used. We could likely grade ferments A,B or C and use different distillation parameters depending on how they look during a micro distillation of the ferment with the birectifier.]

Returning to our subject, we said that by avoiding the entrance to the still of the materials suspended in the fermented liquid, we would greatly avoid the “tufo.” In the same way we can say that we would also preserve the cleanest still, whatever its type.

How to get rid of this material in suspension that is not only dirty and encrusts the device but also causes 90 percent of the “tufo” in the distillate? There are two main means: (1) a good decantation, (2) by total filtration of the liquid, and of these two means, undoubtedly the second is the best and most effective. We do not know of any distillery in the country that practices the filtration of fermented liquid before its distillation, but our experiments to this effect have more than convinced us of the great effectiveness of this practice in terms of its influence on the quality of the distillate, and the preservation of the still free of dirt and scale, the differences in the distillate are appreciable at first glance.

[This is a big refutation of distillation on the lees and a hallmark of Arroyo’s ideas. Eventually he advocates for a small scale Westfalia type continuous centrifuge for distillery use and then back tracks a bit and favors decantation for pragmatic purposes.]

When we are dealing with the curing of raw rum, we will see that in this later stage of rum manufacturing the effects and consequences of having or not following this practice will be felt. We will also notice the importance of being able to distill to low proofs, which depends in large part on the formation or not formation of tufa when doing it.

[Use the birectifier to grade ferments A,B, or C!]

If, as we have experimentally proved, 90% of the “tufo” comes from the overheating suffered by substances during the distillation of the product, we will see that it is worthwhile to seek the elimination of these substances before entering the still, and these means we have indicated. Now we will ask—where the other 10 percent remaining of the “tufo” comes from, because the remaining 10 percent comes from the products of secondary fermentations, or impurities inherent to the raw material, for example presence of sulfites in the final molasses, or of some primary fermentation products, which we have not had the ability to avoid during fermentation, or to separate during distillation. The difference between one and another cause or origin of the ferment is that 10 percent is formed and dissolved in the fermented liquid, while 90 percent is formed in the same alembic during distillation. Both one and the other are unnecessary and completely avoidable.

[See: Presence Of Acrolein Derivatives In A Rum Of Abnormal Taste]

In addition to being influenced by the distillation by the suspended solids of the fermented batición, it will also be influenced by the degree of alcohol content and its congeners, as well as by the quality of the dilution water used during the preparation of the batición. This water usually influences in two different senses, because if it is heavily laden with mineral salts it can significantly help the encrustation of the plates of the column in the case of stills of continuous distillation, or of the boiler in the case of batch distillation; and this water can also bring strange and harmful organisms, capable of generating secondary fermentations, whose products contribute in part to the formation of undesirable odors.

How to conduct the distillation to obtain the best results? It would not be possible in a necessarily condensed article to give in detail all the precautions to be taken in the handling of the different types of distillation apparatus; but we will mention general lines of conduct to follow in the distillation of rum, applicable in any case.

We have already discussed the advisability of eliminating, as much as possible, the solid matters of the fermented liquid before giving it entrance to the alembic. It is important that distillation does not be forced in no time; it must be rhythmic, slow, rhythmic and uniform. In particular, distillation should be carried out slowly at the beginning and end of the distillation, and during the intermediate time it should be possible to conserve the same volume of distillate per unit of time. The distillate test marked by hydrometer should be between the degrees of 160 to 170 P. in the case of working with continuous distillation apparatus; although this degree can be reduced with certain devices and taking the necessary precautions. As we said before, working with appliances with batch distillation, the degree of distillation test may be lower than in the previous case without affecting the quality of the distillate. It is convenient for several reasons to work at the lowest test level compatible with the production of a good rum. This precaution will have considerable importance during the subsequent process of curing fresh rum. Another point of importance that is rarely taken into account is that of the temperature of the cooling water when leaving the final condenser. This should not come out cold, not even fresh, but tempered, approximately between 45 and 50 degrees Celsius. The refrigeration of the mixture of vapors that enter the final condenser, and that condensates have to constitute fresh rum, to be of good results, must be carried out so that this condensation is not sudden, but operated gradually, methodically. The coolant must be fed in such a way that the lower part of the condenser remains cool, the middle part is warm, and the upper third a little hotter. An excess of cold in this operation will impart hardness to the fresh rum that distills, unbalancing its “bouquet”.

When using a batch distillation still, the degree of distillation proof can be easily regulated, using greater or less total reflux before beginning the distillation itself. In the same way we can regulate the relative volumes of products of head, body, and tails. It is also extremely easy with these apparatuses to modify within a wide margin the chemical constitution of the distillate, given its great flexibility of handling. The ratio between the volume of fresh distilled rum and the time it is distilled can be varied at will. In our semi-commercial still we have made distillations at the rate of liter for every five minutes, and also for liter per hour.

One of the biggest advantages of a discontinuous batch distillation still for rum is the ease with which we can separate from the tail products, those harmful from ones that can be useful to us. Harmful tail products generally end their distillation when the hydrometer marks around 30-40 P. From this point until it reaches zero, the products that distill change their aroma surprisingly, which becomes smooth and pleasant. It is very useful to collect these slightly alcoholic waters in a separate container; but loaded with essential oils, higher alcohols of very high boiling point, and valuable esters; also of high boiling point. The use we can give to these “tail waters” we will discuss when dealing with the curing of raw rum.

[Follow the logic here, he says END at 30-40 P, Arroyo is advocating the creation of un-traditional special fractions and we may be seeing some new producers using similar methods in their Queen’s share rums.]

We close this chapter with the following summary, derived from what we have explained here and from other personal experiences:

1. In the case of the manufacture of rum, the distillation is a selective and rectifying extraction process, by means of which we can improve the good rum or correct (as far as possible) the defects of the bad rum. But good, or bad, raw rum is formed at the end of the fermentation process.
2. The fermentative process has a great influence on the distillation.
3. The post-fermentative treatment of the fermented material is of great importance also in the distillation stage.
4. The distillation method to follow needs study in each case separately; but in general terms we will say that when the quality of the product is the most important factor, then we would recommend the batch or discontinuous distillation system; as it is also called.
5. The economic advantages and compactibility of the system to continuous distillation are undeniable and apparent. For mass production this system is the superior. We believe, however, that even in this case, it would be convenient to use both systems, having one still of each type. The continuous distillation to maintain a productive scale, and the batch distillation to produce the desirable grade of quality. Judicious mixtures of both products would lead us to the production of good quality rum on a large scale.


The purpose of this process is to provide the fresh distillate with the acquisition of the maturity, body, soft taste and aroma that characterize a genuine rum of the highest quality. We have chosen the word curing instead of aging, considering it more appropriate.

It is not the greater or lesser number of years in storage only that which imparts the necessary maturity to a rum, since there are those that in a short time acquire the necessary properties to be called añejo; while others of much more time getting older do not reach the balance of constitution, nor do they acquire the other conditions mentioned above to be called cured or mature rum. Everything depends on the state of the crude distillate at the moment of its packaging, the balance existing between the numerous substances that form its “bouquet”, and the very nature of these substances. The conditions to reach the state of optimal maturity in greater or lesser time, the distillate receives them during the fermentation, and improves them and readjusts them during the distillation, if this is well conducted, which is why we could say that the rum curing in certain cases starts in the fermenters.

[Profound, and Arroyo’s language wards off the overzealous claims of the accelerated agers. Many rum producers getting caught up in the age statement game need heed Arroyo’s advice and emphasize curing over aging.]

We have tested this fact with fermented and distilled rums during our experimental work, which after being examined by experts from Hamburg, Germany, were declared exactly of the same quality as the original old rum from Jamaica, imported there. The most curious thing about this test was the one that, according to the expert, our samples showed to be a mature rum, of long years of aging in oak barrels, when in fact the samples only counted six or seven months of having been distilled. That is why we repeat that not only time gives the character of old age or maturity to a rum. The fresh rum must be packed in conditions of being able to acquire its cure quickly.


There are those who believe that the good taste and aroma of rum only exist when they have been artificially incorporated or when they acquire them after long years of barrel aging. In this view there is no reason the fresh rum, well fermented and better distilled in the appropriate alembic, brings with it its distinctive aroma and taste; aroma and taste that we would only damage with the incorporation of foreign bodies; and that, of course, proper aging perfects and softens. But neither the artificial “aggregates” nor the barrel years alone can make a good and genuine rum from a distillate devoid of the indispensable qualities of a premium product. It is as if we were trying to turn a child lacking in natural intelligence into a prodigy by dint of teaching. The rum that has to be good later, it is already in principle, finished at distilling. All further treatment only improves, highlights, and develops its inherent qualities of kindness.

Let’s see now how we should conduct the process of curing or maturing the crude distillate. There are two fundamental methods of curing: (1) the slow and (2) the fast or accelerated. The first consists in leaving mostly the action of time and the barrel to operate the changes in body, taste, aroma, softness, constituent balance and other conditions, which differentiate the cured and ripe rum from the fresh distillate. The time, more or less long, necessary to reach the desired result is regulated by: (1) the quality of raw rum: (2) how it is diluted before being packaged; (3) quality of the oak barrels used for this purpose; (4) previous treatment given to the barrels; (5) size of the barrels; and (6) climatic conditions of the storage site.

When the raw rum is of good quality, for example, limber, crystalline, lacking in “tufo”; of pleasant taste and aroma, of the necessary degree of acidity; distilled to relatively low tests (between 150 and 160 P.) and possessor of an adequate content of rum oil; then more than half of the work is done; Subsequent success is a matter of careful treatment and attention to detail.

An operation apparently as simple as diluting raw rum before its packaging in the barrels, can spoil much of the work done during the fermentation and distillation. After having thoroughly checked the internal difficulties in the chemical structure of rum, caused by this dilution that is customary to do, we are carrying out certain experiments aimed at avoiding them; but of which we are not yet in a position to make public statements.

[Eventually a paper was written and more information provided in Studies on Rum.]

We will explain what happens to a quality raw rum when we reduce the alcohol content with the diluent (almost always pure water) before submitting it to the container and storage. The higher the quality of the crude distillate, the more it is exposed to suffer with this treatment. On the other hand, neutral alcohols, having nothing to lose, are not affected in the same way and special precautions are not necessary when diluting them. With raw rums of real quality, we can not take too much precautions; all are few and inefficient.

When diluting a quality raw rum (at 100 or 110 P.) before being packaged in the curing barrels, we almost always unbalance its “bouquet” and taste, due to two different causes: (1) by dissociation of part of its aromatic esters, and (2) by separation of certain essential oils, including rum oil. Neither one nor the other is apparent to the naked eye. Firstly, it is due to the hydrolyzing action of the water that separates the ester into its two original components, acid and alcohol; and the second one is due to the fact that these essential oils are difficult to solubilize in water, and when they receive dilution, sometimes cold and abruptly, they are separated from the group of bodies that in the rum form the characteristic aroma. These oils are present in such minute quantities that their separation goes unnoticed; and this separation is all the easier because the aromatic whole of a freshly distilled rum is, under labile conditions, unstable, in a state of readjustment, in which the slightest unbalancing factor can bring about the dissociation of the whole. The loss of esters during the dilution and subsequent time until after the first three months, will vary according to the original content of the distillate, method used in the dilution, nature of the solvent, and its temperature and quantity. We have found losses from 20 to 60 percent of the original content, calculating absolute alcohol content in rum before and after dilution.

[This is why it is important to strive to create fermenations you can distill as close to bottling proof as possible.]

Is it possible to prevent this harmful action of the diluent? To that end our current experiments tend; but for the present we can say that it is possible to at least reduce it. This is achieved by taking the necessary precautions when diluting. First of all, whenever possible (and in this the small producer has the advantage) it is convenient to replace “WATER OF TAILS” or water alcoholized to between 30 and 40 P., by pure water, in the process of dilution. These alcoholized waters, or better yet, “tail waters” (of which we have already dealt) will be kept in large oak tanks, and will be used after aging for as long as possible. In this state they constitute the best diluent for raw rums.

[Arroyo had already briefly hinted at the production of special tails fractions and here we see them coming into play.]

Not being possible, or being cumbersome the use of these aged liquids, we will have to resort to water as a diluent. If we have to use water, it must be of the highest purity obtainable; preferably distilled.

Whatever the liquid used of the three mentioned, the dilution should be conducted from the following, or similar mode: The distillery will have a special room for dilutions, conveniently equipped. First of all we will have an oak wood tank equipped with agitator and heating unit, in which the temperature of the diluting liquid will be raised about five degrees centigrade above the temperature of the raw rum that will be diluted. This tank will be located at a higher level than the one in which the dilution will be made; which will also be built of oak wood of the best quality. This tank will be connected to the diluent tank by means of a thin tube of tin, or tinned copper, which will end up in the form of a ring at the bottom of the dilution tank. This ring will be full of small perforations through which the diluent will enter the tank that will already contain the raw rum that has to be diluted. A mechanical agitator will keep the mixture of raw rum and diluent in continuous slow motion, during the entire duration of this operation. We must warn that all this process must be carried out slowly, without any hurry, because the slower the incorporation of the diluent to the diluted, and the thinner the holes of the feeder ring of the diluent, the better the results obtained.

[I have never actually seen this described. There are lot of metal “foams” used to dissolve gases in liquids. It would be interesting to know if there is any great off the shelf modern way to get good results.]

When in our previous section we said that it was convenient to distill the lowest proof compatible with obtaining a good raw rum, one of the reasons we had in mind was this necessary dilution before packing in barrels. Why not pack without diluting? There is no doubt that from certain points of view this method would be very convenient. In the first place there would be no alteration of the constituents of the crude distillate, nor the imbalance in aroma and taste. At the same time we would have the additional advantage of using fewer numbers of barrels, and that the cure would proceed with great increase in the ester content due to the elimination of the hydrolyzing action of the diluent. But on the other hand, we would find that unless we distilled to a very low proof, we would always be forced to carry out the dilution process after the rum was cured, with which we would not advance anything. Other drawbacks would be the greater alcoholic loss during the storage time and the greater care that would be necessary to take in the selection and preparation of the container barrels. Another method to follow would be that of partial dilutions extended during the curing time; but undoubtedly this method would be difficult to carry out, perhaps requiring a special design of the storage site. The ideal would be to distill quality raw rum to proofs low enough to avoid having to dilute the distillate at any time; This is possible! We can not assure you at the time of writing these lines; but that is one of the most interesting points of our investigations.

[It is extremely cool to see these guys getting excited at the very end of this paragraph. To my knowledge, cachaça and tequila have achieved this goal more than anyone else.

Following the current practice of dilution with water before bottling in barrels, it is easy to conceive that the less diluent we have to incorporate into the crude distillate, the lesser effects will be less, and the less time we will lose in the dilution process.

Once the raw rum is diluted to the right degree to be packed, the next question is—what will be the best container to use? We all know that white oak barrels are the right ones; but among these there are great differences. There are of all sizes, charred, without charring, paraffinings, etc.; the quality in each class also varies considerably. All these differences between the barrels of the trade will be reflected in the distillate during its cure. In terms of size, we must first be guided by the quality of the rum we want to produce and the probable time we need to keep it in the barrel to acquire it; therefore this is an issue to be decided particularly in each case. The goodness qualities of the crude rum will serve as a valuable guide in the selection of the size. Of course, here economic issues also enter; but like the first ones, these are to be solved in each case. In general, the small capacity barrel accelerates the curing of rum; but instead it offers greater evaporation losses, higher initial cost per unit volume, and more handling costs. The charred barrel inside accelerates the curing of the distillate, and if the rum contains “tufo”, it tends to be eliminated or attenuated; but we do not recommend it to age rums of first quality, especially of those destined to appear among those of “light types”, because the curing in charred barrels gives them a very high color and body and too much wood flavor with “whiskey” characteristics. These bad results can be mitigated, however, by special preparation and conditioning of the barrel before admitting raw rum into it. As for the barrels covered inside with a film of paraffin or sodium silicate, the only great advantage they offer is to prevent undue coloring of the distillate and large alcohol losses by osmosis and evaporation. They allow the aging of the crude distillate, much more slowly and incompletely than in the case of the other barrels. We think that the best would be a discreet use of the three kinds of barrels mentioned; especially to avoid having to use artificial coloring to obtain a uniform and invariable color in the cured and bottled rum. We say this because we have observed that all barrels of the same class are not enough to obtain a uniform and invariable color in the finished product, since there will be notable differences between batches and between individual barrels within the same batch.

[I have only every heard of parafin lined barrels for grappa. Ideas like paraffin or sodium silicate were likely used in barrels across many industries besides distilling.]

The quality of the barrel itself will depend on many factors, some of them outside our domain or intervention. Among these we will have, region and climate where the trees whose wood came into the construction of the barrel were produced; age of these trees when cut; way they were cut; site of the tree that occupied the wood with which the barrel was made; existence of knots, of resins; content and variety of extractive materials; time when the wood was cured before the barrel was made; and above all, the conditioning method used in the distillery before admitting the barrel to the crude distillate.

After conveniently selecting and treating the barrel, we must take the precaution of not filling it completely when packing the raw rum, to facilitate expansions that result from changes of temperature during the hot hours of the day, and also to allow free access to the outside air through the pores of the barrel. Finally, the storage site of filled barrels requires careful selection, not being excessively dry or humid, and with free admission of fresh outside air.

How is the rum improved or cured in the barrel? The phenomena of curing are not fully understood; There is much to learn and find out in this regard, and without a doubt deserve careful study. But in the light of what little we know, we can say that this curing operates insensibly within the liquid contained in the barrel, and that we can attribute to the following factors: (1) the slow evaporation of a portion of the alcohol, thanks to the porosity of the barrel and temperature and humidity state of the environment; (2) to the dissolution by alcohol of certain constituent principles of oak wood; (3) to a series of combinations and chemical condensations, developed either by the reciprocal action of the constituent elements of the raw rum, or by the influence on these same elements and their combinations, of the oxygen of the external air that is filtered through the pores of the barrel to exercise its oxidizing character; (4) to the state of equilibrium in which the components brought by the distillate and acquired from the barrel finally arrive; (5) at the prevailing temperature at the site of storage, as is known, heat is a great auxiliary for chemical combinations. We must be very careful with the degree of heat to sustain, because sometimes the losses in alcohol mean that its immoderate use is not remunerative.

Let’s now treat the method, or methods of rapid or accelerated curing, lightly. All the rums are not destined to acquire their maturity under the slow and smooth, but sure action of the time and the barrel. Our era is one of impatience and acceleration in all orders of human development, and the curing of rum is no exception to this trend, in the vast majority of cases.

The demands of trade, the lack of ample capital, adequate technical advice, the ever-increasing needs of consumption, competition, oblige manufacturers to put their products on sale in the shortest possible time. As a result of the above, the vast majority of our rum producers strive, in various ways, to provoke in the short term the characteristic transformations of a mature rum, and even to communicate them by additions of different compositions, the approximate taste (see well our readers that we say approximate taste) of the genuine rums. In our opinion, the results so far obtained in this order of ideas are very relative, insufficient and mediocre; leaving the problem of artificial aging without satisfactory solution to date.

[1938 folks!]

We do not deny, however, the possibility of improving defective rums by these rapid procedures; and we would be the first to appreciate and applaud the advent of an accelerative process that would offer us cured rums of equal or superior quality to those obtainable by slow curing. That would be a great advance in the manufacture of rum, and all progress is good. That is why we will lightly review the quick methods employed, of which we are aware. These vary as much as there are rectifiers; but all obey general principles.

The rapid curing processes can be divided into two main classes:

1. Those whose purpose is to accelerate the work of curing time and barrel without adding to the distillate of foreign ingredients that carry aroma and taste.
2. Those who besides operating as those of the first group, use the addition of strange elements.

The raw material class in the form of crude distillate, which is at the hands of the rum maker rectifier, will influence the choice of the method to follow between the two large divisions that we have explained above.

Fast-curing processes are almost always used on two different kinds of distillates. The rectifier, (and especially the one that does not distill its own raw rum) usually has a defective raw rum, or a rum so purified that we could call it reduced alcohol. In the first case your first care will be to remedy the defects by chemical, physical, or various combinations of both methods; in two words, eliminate the “tufo” in any possible way. In this endeavor almost always end up eliminating the “tufo”, and thus also the constituents of aroma and taste that should not be eliminated with this one. It no longer exists, but neither does the inherent aroma of the rum, the main care then being to impart to the reduced alcohol flavor and “bouquet” of ripe rum. This is not as easy as many believe, imparting the genuine taste of ripe rum to a reduced alcohol has not been achieved by anyone yet, for this the chemical synthesis of “rum oil” would be necessary, something that has not been achieved because its structural formula is unknown, and even after carrying out this synthesis, other quantity factors would intervene, relationship to other components etc., which would make the task sufficiently arduous and difficult. What is easily achieved through the use of reduced alcohol is the composition of an alcoholic beverage that is actually a liqueur or cordial, we opted to call rum.

We do not want to give the impression in any way that we think that these drinks are bad. Perhaps in some cases they have, for many, a more pleasant taste than that of a genuine rum; but in no case will they know the true rum.

That is why we must make a distinction between accelerative methods that tend only to lighten the work of time and the barrel; but that they do not incorporate strange elements into the rum to give it aroma and flavor; and those that we just discussed. But to make use of the latter it is necessary to start with a crude of excellent natural quality, which is rare in our market. In these cases we make use of the heat, the intense cold; alternatives of heat and cold; air under pressure; the effects of electric current; catalytic agents in combination with certain activated-carbons, etc. We also try to replace the action of slow oxidation of the oxygen contained in the air, with a rapid and intense oxidation based on oxygen gas, ozone, or hydrogen peroxide. We do not even want to mention the use of other chemical substances that are harmful to the human economy, consider it out of place in this article.

Among the list of substances added to raw rums during rectification in some cases, we have in the first place the sugars, in the form of sucrose, syrups of various kinds, dextrose, molasses, etc. After a whole series of extracts of flowers, leaves, bark and roots; most completely harmless and even beneficial to the human organism. Followed by wines and cordials imported or manufactured by the same producer of rum.

We believe that these practices are not condemnatory as long as they are limited to the use of botanical products that are harmless or beneficial to the human body, and others such as generous wines of recognized goodness; But what we do assure is that to date the best method of curing is that which is left in the hands of time and a well selected and prepared barrel.


This phase of the rum manufacture has not yet received general acceptance in our Island. It is carried out in a more or less rudimentary way in rare exceptions. We could say that the rum industry currently occupies the level of development that the sugar cane industry had thirty years ago, as far as the supervision methods are concerned. As we said before, there are well-known exceptions.

[In 1938 would Bacardi be the exception? Any others?]

The great alcohol industry in the United States recognized from the beginning the basic need for such supervision, and with personal experience on this matter, we can assure that in any of the great distilleries of industrial alcohol in the United States, the technical personnel outnumber the worker. This data will give a good idea of the importance that is granted there to this important phase of the industry. However, the rum industry needs much more of that supervision than industrial alcohol. It is easy to compete in the industrial alcohol market, but very difficult to do so in the rum market. We hope and trust that just as the sugar industry of thirty years ago gradually realized the importance of supervision in the manufacture of sugar, so the rum industry will awaken to the realization of this need in the course of next years.

[On the continent, much super technical super vision and advice came from the IRS excise agents themselves.]

As in all other stages in the manufacture of rum, it is also not possible to give rules and fixed methods of regulation that fit all the distilleries, since the personal conditions, equipment, methods of elaboration, and quality of the final product, usually vary enormously in each case. We will limit ourselves, then, to offer general ideas, leaving their modifications and adaptation changes to be judged in each case according to desire or convenience.

Is this supervision necessary? There is no doubt about this; Well, how could we work intelligently without knowing the chemical composition of our raw material, its physical characteristics, its microbial contamination, on the one hand; and of the other not knowing also the biological characteristics and chemical products of the ferment that has to operate and transform this raw material? On the other hand, how could we follow the course of the process and know its status at any given moment, without taking a supervision that guides us and warns of the pitfalls and dangers to be saved? How to avoid contaminations whose origin we do not know? How to get characters in our product incompatible with the nature of the ferment and the environment in which it develops and does its work? What will guide us to make changes or introduce useful and necessary innovations? How to know the true basic yields, the losses, the causes of these losses and means of correcting them, the fermentative and distillatory efficiencies, without adequate supervision?


Given the admitted need for chemical and biological monitoring, where should each phase start and end? We can indicate that the supervision begins with the selection of the yeast; finishing the biological phase with the entrance of the fermented liquid to the still; and the chemical phase when bottling the commercial rum cured.

Let’s see how this supervision influences and provides service in the different stages of the manufacture of rum:

Biological and chemical factors are involved in the selection of the yeast, since we can choose high or low fermentation yeast; slow or fast; of high resistance to contamination or very sensitive to them; capable of development in very, medium, or slightly acid media; adaptable or not to high concentrations of sugars, etc. All these qualities and aptitudes will be determined through the application of biological supervision. On the other hand, we have to choose between yeast producing little or many esters, higher alcohols, aldehydes, essential oils and other congeners of ethyl alcohol. We can also choose the classes of esters that are the main products of different yeasts. Here chemical supervision comes to our aid.

In the selection of the raw material we will also be guided by its chemical composition, and this knowledge will put us in condition to calculate the probable yield in rum that we will obtain, and calculate the amendments that we have to make to obtain the highest possible efficiency during the fermentation. We wish to indicate here that the raw material must be examined in terms of its content in total sugars, nitrogen, phosphoric acid, gums and ash. In addition, its pH value and natural aroma must be determined. All this belongs to chemical supervision. On the biological side, a still superficial examination of the character and extension of the microbiological flora that accompanies the raw material, will serve as a guide in the class or intensity of the pretreatment to which we must subject it.

In the process of preparing the batición, this supervision intervenes again. We need to know the quality of the dilution water from the chemical and bacteriological points of view. In addition, it is necessary to assess the efficiency of the pretreatment process before diluting. Only a count before and after the pretreatment will assure us of the success obtained in terms of the elimination of microbial life. We also have to determine if the batición is in optimal conditions for it to develop a normal and vigorous fermentation. The knowledge of its content in total sugars determined in grams per 100 milliliters is very useful, since it will give us the base to calculate the total content of sugars in the batición in pounds or kilos. In this way we will know for sure the amount of sugars that we will give in the fermenters to the action of the yeast. This data will then enter the calculation of the yield based on total sugars.

From the analysis of the raw material we can calculate the probable deficiencies of nitrogen and phosphorus in the batición without having to resort to new determinations; But although we could also reach the determination of the sugars in the batición, it is much more convenient to make a direct analysis in this case, given the importance of this data in subsequent calculations. Therefore, we believe that in the case of preparing the batición, we should make the following determinations: pH value; density by Brix hydrometer; titratable acidity; and total sugars by the chemical method of Eynon and Lane.

During the fermentative period we must record data on the date and time of inoculation, and time at which fermentation begins in each fermenter; as well as the percentage and age of the yeast footing used. Partial attenuations will also be noted during conventional time periods; variations in pH value; in temperature, and titratable acidity. After the fermentation, the date and time will be noted. A sample of each fermentor will then be taken, in which pH value, final Brix, titratable acidity, residual total sugars, and alcohol will be determined by volume and by grams in each 100 milliliters of fermented batición. The characteristic aroma of the fermented liquid will also be observed.

[I suspect that titratable acidity is the big one here. The Δ of the titratable acidity, beyond the baseline of what yeasts produce can imply the positive or negative contribution of bacteria. This data as well as pre-screening a fermentation via micro distillation with the birectifier can help us categorize ferments as A,B, or C and optimize distillation parameters to get the best out of each ferment.]

The data obtained from initial and final brix will allow us to calculate the total attenuation; the determination of residual sugars will facilitate us to calculate the percentage of fermented sugars; the determination of alcohol by volume will facilitate the calculation of the gallons or liters of alcohol that will enter the distillation process; and finally the determination of grams of alcohol per 100 milliliters of fermented liquid will give us the data to calculate the yield by weight, based on pounds or kilos of total sugars in the original batición; and about sugars currently fermented. Once the yield per weight in alcohol is known, the percentage of fermentative efficiency will be calculated.

[A,B, or C distillation routines have different cuts made by absolute alcohol in the heads. Knowing the volume of absolute alcohol put into the still with inform these decisions.]

If we want a safer and more delicate chemical monitoring during the fermentation process we will resort to periodic determinations of total sugars, alcohol by weight, pH value, and titratable acidity. With these data we will construct fermentative graphs that will give us with certainty at any given moment, the relation between destruction of sugars and alcohol formation; as well as corresponding changes of pH values and titratable acidity. This graphical picture of the fermentative process is of great value and utility to discover abnormalities and harmful incidents that may occur during the fermentation period. The invasion of the batición by foreign organisms or adventitious yeasts will result in remarkable alterations in these fermentative graphs.

[These graphs are a big part of the work in Studies on Rum. These days the biggest distilleries create them real time with inline spectroscopy that works based on models created from chromatography.]

In this stage of rum manufacturing, biological supervision plays, as chemistry also plays, a major role. The first care is to preserve the yeast footing or yeast seed in optimal conditions of purity and cellular concentration. For distilleries equipped with pure yeast machines, the task is relatively easy, especially if the “Magné System” machine is used. Otherwise, the constant attention and alert of the bacteriologist or fermentologist in charge of the process is needed. To this end the footing will be examined at frequent intervals under the microscope while it is in preparation, and especially shortly before the time of inoculation. At this time the footing must have reached its maximum active cell concentration, and must present a large majority of young and active cells. Above all, it must be completely free of contamination. Otherwise, the footing should not be used, since it is equivalent to sowing a field with bad seed. These microscopic exams will give us a general idea of ​​the state of purity, especially in terms of contamination caused by fungal spores or bacteria; but as for infections with adventitious yeasts, unless they differ markedly from the morphological point of the culture yeast, microscopic examination loses much of its value. This is because it is very difficult, even for the experienced observer, to determine morphological differences between similar yeasts. There is also the disadvantage that the same type of yeast offers different cellular forms, depending on age, nutrition, access to oxygen from the air, and reaction of the medium in which it is found.

[Fascinating and I’ve never seen it spelled out like this at the end. I think the big advancement for present day small distillers will come from the use of disposable yeast bags. There are lots of disposable products for biological work that no one is taking advantage of. After I finish enough birectifier exploration, this is where my personal focus will migrate.]

There is a simple means, however, to determine the presence of adventitious yeasts in the culture, which is called the sporulation test. It is known that different strains of yeast are conducted differently in this test, there being great differences between the yeast culture and any adventitious yeast. There are yeasts that form spores in a dilated time, or in special culture media; others that sporulate in very different time lapses; others that although similar in terms of time required, the spores differ in their position in the cell, in number, and overall appearance of refractivity, size etc.

Now, if the distiller knows the biological characteristics of its yeast, it will know, of course, all the necessary conditions for its sporulation. When doing the test with a sample of the footing or the fermenters, in the usual block of gypsum, it will be realized, by means of microscopic observations if cells with spores appear in a lapse of time different from the usual one taken by the yeast of culture; or if between sporulating cells there are spores with different characteristics than those already known as inherent in their culture. In this way you will know whether or not there are contaminations due to adventitious yeasts. Of course, when the morphological differences are very marked between the yeast of culture and the adventitia, we can pass without the sporulation test, being then simple the simple microscopic observation.

[Old school, and I personally need to learn a lot more, but I suspect this kind of analysis is still very helpful.]

These biological examinations should be carried out periodically during the fermentation and if the other treatment that we have already talked about is being used in the distillery, then this supervision should be extended until the time of the distillation process. The infection of fermented material is much easier to occur after the yeast has finished its fermentation process, especially the infection due to Mycoderma Aceti, which oxidizes the alcohols to acids. In case of finding signs of a dangerous infection during the rest treatment, what can best be done is to submit the fermented liquid to the distillation process as soon as possible.

By means of the chemical supervision that we have been pointing out in the stages preceding the distillation process, we will know the gallons of alcohol contained in the fermented liquid that we deliver to the alembic. Once the distillation is complete, we will know the percentage of alcohol actually recovered by the distillation apparatus. The difference between gallons of alcohol brought into the liquid and measured after the distillation represents the alcoholic losses during the distillation process. From these data we will calculate the distillation efficiency of our still. The general efficiency of the process will be this distillation efficiency multiplied by the fermentative efficiency.

[Many people are forgoing this kind of simple analysis, but it will become important as tasks are delegated.]

The crude distillate must be analyzed before dilution. This analysis will include test determinations; alcohol by volume and grams of alcohol in 100 milliliters; aldehydes; esters; higher alcohols; furfural, total acidity, and organoleptic determinations of aroma and tasting.

[Few new distillers work at a scale where they can perform these titrations. It is really wild when you try and put a dollar value on how much it would cost to precisely measure them in house. A precise automatic titrator for acidity runs $3000-5000. The birectifier opens the doors to organoleptic determinations and it may be the most pragmatic set of methods available. Some tests, like the exhaustive test can fill in for titration until an operation is sophisticated enough.]

During the distillation, precautions must be taken against the loss of alcohol. These can be accidental or due to unsuitable operation of the device. Among these losses are those represented by small leaks in the column, condensers and other gadgets of the alembic; the one that can and usually exists in the must (slops) that discharges the alembic; and by deficiency of refrigerant in the final condenser. Of these losses the most important is usually what happens in the musts; which must be reduced to a minimum percent. This tends to be higher in a continuous distillation still, sometimes reaching alarming proportions if they are not well conducted. To avoid this loss, alcohol determinations will be made on samples of the musts as they flow from the still, and distillation will be carried out according to the results obtained from these analyzes.

Losses of a mechanical nature must, of course, be corrected as soon as they are discovered. As for the losses resulting from refrigeration deficiency in the condenser, they can be caused by a forced march of the distillation, due to lack of cooling surface; by reduction in the injection of the refrigerant, or by the temperature of it when entering the condenser. Obstructions in the piping or valves that regulate the intake of the refrigerant can cause a great decrease in the volume of water that enters the condenser, thus producing the excessive elevation of the temperature of the distillate.

It would be convenient, therefore, to regulate the temperature of the water leaving the condenser, which would warn us of any abnormality of the refrigerant process. It is also important to regularize the temperature of the condenser outlet water, as far as the quality of the distillate is concerned, as we already explained about the distillation. Once every 24 hours a qualitative test will be done to determine the presence of alcohol in these waters. If it produces positive results it will indicate faults in the condenser.

[This is not to be glossed over. Anecdotes I keep hearing show that many are distilling too swiftly and challenging their condensers. These days we could put a PID on a pump correlated to the outlet of the condenser and keep consistency easily.]

During the curing process, chemical supervision still continues to play an important role. We have mentioned that the crude distillate must be analyzed before its dilution, and the necessary determinations indicated. From the analysis of the crude distillate we will obtain data to calculate the yield in rum or alcohol to a certain test; calculate the distillation losses and the efficiency of the still. This analysis will also give us knowledge of the composition of raw rum. We have already explained that during the process of dilution of the distillate, if we do not take the measures of rigor, we can alter notably the balance of chemical composition, especially as regards the amount of hydrolysed esters. It is convenient, then, to reanalyze the distillate once diluted before being packaged in the curing barrels. Calculating the analytical results based on absolute alcohol, before and after the dilution, we can appreciate the extent of the changes suffered in the chemical structure during that treatment. This will serve as a valuable guide to improve as much as possible the conditions of the dilution process and introduce innovations in it. The better the process has been done, the less alterations are found in the analytical results when checked.

In addition to these chemical tests, physical and organoleptic observations must be made in the crude distillate, before, and after dilution. For example, we will take note of its color, limpidity, viscosity; as well as taste and aroma. Sometimes noticeable differences may be noted in these tests, before and after the dilution, which will be an index of the efficiency with which this treatment has been carried out.

There are other important tests to which the crude distillate should be subjected before being packaged; as the fractional distillation by means of the birectifier, the “bouquet” test by means of the action of sulfuric acid at 50 percent concentration; the one of aromatic persistence through systematic dilution; the determination of the presence or absence of rum oil, etc.


[I have slowly tackled all of these. The birectifier is the game changer. The sulfuric acid test has left a little to be desired, but is quick and easy to perform. The exhaustive test takes a little getting used to but is extremely powerful. There are also tests for surface tension which can imply the presence of long chain carbon stuff, and I’m developing a test for fixation which would imply the content of rum oil and long chain esters using an analytical balance.]

Once the rum is stored to continue its curing process, it still needs chemical supervision. It is convenient during this stage of the manufacture to make more or less complete analyzes of the different batches of barrels filled with the raw product. Each lot must have a number and an open history in the supervisory laboratory. In this history, the distillation date will be stated, the degree to which it was distilled; date of the container; and the results of the chemical, physical and organoleptic tests carried out on the crude rum; as well as volume of the packaged distillate. This record will continue to be expanded with similar data collected during the total duration of the curing. For example, every two or three months a representative sample of the lot will be taken, and the tests already carried out on the raw distillate will be repeated. In this way we will follow step by step the transformations of the curing and we will know how the maturity of the product progresses. This work is very interesting and useful because it offers us valuable information that we would never otherwise know. We will find out if we carry out these tests, that the hydrolyzing effect on the esters caused during the dilution of the crude rum, extends to a period of not less than three months and thus also the other evils caused by the dilution; which is why we will often find that after aging for three months, the curing results are negative, at least in terms of the chemical composition of the product.

To conclude this chapter, we wish to point out that in our humble opinion the distillery should not only have a competent technical staff to carry out the supervision we have outlined, but should also have a separate body of technicians, dedicated exclusively to research work. If any industry needs this kind of work, this is one; if one keeps in its bosom optimal and tasty fruits for the researcher, this is one. The field is completely virgin; scarcely have the first, hesitant steps been taken; everything is to be discovered and resolved. We need to do fruitful work that can transform this young and vigorous industry into a perennial source of wealth and prestige for the native soil.


In short words we would answer that the best equipment is the one that offers the most facilities for the production of the desired rum type.

How many times have we had occasion to deal with this issue with presumed producers, we have been able to observe that the predominant idea to them, what will evidently decide the success to failure of the company, is the still for which they have to decide.

Will I buy a French, German or American still? What nation makes the best? These are questions we have heard many times; and invariably we have answered that whatever the nationality of the alembic, or the production house chosen within the same nationality, in all and in any of the apparatuses can be distilled good rums and bad rums.

Of course, there are good, better and worse distillation devices; but only this part of the equipment should be given the importance it deserves. That this importance is great, is undeniable. The quality of the rum will not depend on the greater or lesser complication of design and majesty of the alembic’s exterior appearance. Here the significant thing is the type of still in its relation to the class and quality of rum that we wish to produce, and to the economic factors that determine the development of our business. The ideal alembic in one case, may be out of place in another.

Already when dealing with distillation we said that we can produce high quality rum distilled in the simplest types of still; in appliances, for example as those used to produce the famous Cognac from the Charente region, France. Objections to the use of these types of distillation devices are not of a technical nature, nor of inferior quality, but of an economic nature. Using the redistillation as a rectifying principle, they are very inefficient in time and fuel. As for the quality of the product, it can not be better, nor get more demand from the market.

Therefore, in the choice of the still we must consider the following points: (1) class and quality of rum that we try to produce; (2) production volume; (3) method of curing that we will follow; (4) quality of the water that we have in the distillery; (3) economic limit of production expenses. Studied, considered, and resolved these points, then we can decide the still to acquire.

If we are determined that the quality of our rum is the predominant and most significant factor of our business, then the still for batch distillation should be preferred; especially if we do not have a large production in mind. When do we want large-scale production accompanied by high quality? Let’s decide then for the acquisition of both types of alembic; one of continuous distillation to sustain the volume of production, and another of batch distillation to ensure quality. There is a great advantage for large distilleries in which the distillation equipment includes both types of still, due to the combinations that can be made with mixtures of the respective distillates. In this way we can produce several types for different tastes of the consuming public. Do we want a Jamaican type rum capable of competing in quality with the excellent rums produced there? In this case the batch distillation still is the indicated one. In two words, before choosing the still, let’s first decide the rum we want to produce and to what degree of quality we are willing to arrive in its elaboration.

The curative method that we decide to use to mature the crude distillate, must influence the type of still to be used. For example, if we lack sufficient capital to make use of the method of slow curing that we have talked about and we necessarily have to use different “SALSAS” or “BASES” to impart aroma and good taste to our rum, then we consider it unnecessary to install a batch distillation still; The continuous distillation is indicated in this case.

If we have water of defective chemical composition, then the still of batch distillation is preferable, since the plates of the column in the stills of continuous distillation would be encrusted with mineral deposits with great frequency, causing cleaning expenses and frequent losses of time. As is known, the column of the stills with batch distillation is kept clean and free of encrustations for an indefinite time, since only pure vapors are admitted free of all solid substances.

If we have discussed the distillation equipment with preference, it is because, as we said before, it is the one that most public interest seems to have. But what we have said in that case, we could repeat it when considering the equipment of each one of the stages of the rum manufacturing process that we have dealt with in the course of this work. Consider, for example, the selection of the fermenters. These can be closed or open; constructed of metal, wood, or lacquered concrete; provided or not with heating and cooling elements. They may also consist of a few large units, or many small units; in form they can be cubic, cylindrical, conical, prismatic, etc.

In the selection of this equipment we must be guided not by the absolute sense but by the relative one; we can not think of the fermentative process in isolation, but in its relations with the processes that precede it and those that happen to it. For example, what value would closed fermenters have if our plan does not include the biological monitoring of water and raw materials on one side, and on the other, the recovery of carbon dioxide gas generated in the fermenter? The closed fermenter has two main objects: (1) to facilitate the recovery of carbonic gas and the alcohol that it drags, (2) to offer greater protection against possible contamination during or after the fermentation of the batición. But if we do not try to carry out this recovery, or dominate much more likely and dangerous infections from dilution water and raw material, why then closed fermenters?

[Wow!, they were recovering CO2 in 1938. And how much alcohol could be recovered from it? Is this only for econo spirits or has this ever been applied to a fine spirit like Cognac?]

Also as regards supplying the fermenters with heating and cooling elements; we only have to do it when we are able to make efficient and constant use of these gadgets. Otherwise they will be an unnecessary expense and a hindrance.

Regarding the shape of the fermenter, we think that the cylindrical ones are easier to handle when cleaning; but those with the shape of a truncated cone, have the value to offer less surface to contaminations of the environment in the case of using the open system.

For the selection of the number and capacity of the fermenters, if many of them are small, or few of great capacity, there are good arguments for and against in each case. The fermenters in large numbers will occupy more space, they will need more attention, their maintenance in good condition will be more expensive; but on the other hand the losses caused by accidents, or by damaging a batición during the fermentative period, will be of smaller amount. Working under supervised conditions, with very small margin of contamination or accidents; The point that will decide the size and number of fermenters to install is whether we want to work with slow or fast fermentation. Of course, this is largely decided by the type of yeast, as we have already explained, but with a given yeast, the fermentation will be faster the greater the capacity of the fermentor. Now, slow fermentations are indicated, for certain types of rum, and fast for others. From where we return to what has been said in the case of the selection of the alembic: All selection of equipment must be considered in relation to the quality of the rum that we want to produce. Another advantage of the low capacity fermenter is the ease with which we can vary the percentage of the footing of yeast used in its inoculation, if necessary.

Regarding the construction material that the fermenters must be made of, we can say that ordinarily no other advantages are recognized than those of the material that is most resistant to working conditions and climate, and the facilities for cleaning them; but we are carrying out experiments that will show that in certain cases the construction material assumes transcendental importance; to the point that the success or failure of the process can depend on that single factor. In a general sense for present and future developments within the rum industry, we would choose wood fermentors in preference to those of other materials. When in the near future, we expose certain theories and fermentative procedures, now under investigation, we will adduce the reasons for this preference that we give to wood fermentors in the case of manufacturing high quality rum.

[I do not recall Arroyo following up on this, but correct me if I’m wrong.]

The essential thing in the fermentative stage in terms of equipment, is to be able to always count, and at any time with a yeast seed in its state of maximum cellular development and free of contamination. This depends on 75 percent of the success in the fermentation process. The best, (and we could say the only) equipment to guarantee this state of affairs is the machine of pure cultivation; especially if this is one of those of the “Magné System.” These machines are the favorite for their absolute efficiency and guarantee against infections, and for their special method to conserve the crop in its optimum state of cellular development.

This equipment to conserve the culture constitutes the heart of a distillery, and nevertheless, it is the one that less is known about, or seems to worry the presumed distiller. Its cost is comparatively low if we compare it with other equipment, and it has the advantage of being self-liquidating, because of the great economies that in time and higher alcohol yield provides its use in the distillery. With the possible money to be economized in a judicious and adjusted selection of the still, we would have to acquire several machines of pure cultivation.

As we discussed the question of the best equipment in the distillation and fermentation processes, we could review the other equipment used in the stages of pre-treatment, the batición, curing, etc., with which, in each case reaching similar conclusions, only we would tire our kind readers. Condensing, we can say that:

(1) The best equipment is the one that offers the greatest facilities for the production of a certain type of rum, previously chosen.
(2) The equipment in each department can not be considered in absolute, but relative terms. The gear or concatenation of equipment in the various departments is much more important than the individual equipment of anyone separately.
(3) The mere fact of owning a modern and impressive still is not enough to ensure success in the distillery. This device is very important and its selection must be carried out carefully; but its importance is only relative. [Don’t tell the distillery Instagram scene!]
(4) The interdependence of a process with its precedent and with which it must follow in the manufacture of rum, is such that the general efficiency of the distillery will not be greater than that existing in its less efficient department.
(5) The possession of a pure cultivation machine is the indispensable equipment to the good running, and above all to the economy of the process.
(6) A good laboratory of chemical and biological supervision is of great benefit to know for sure the progress of the process, the yields, true, the efficiency of the distillery, the quality of the product; and finally, to guide us in the practice of changes or innovations that result in the general benefit of the company.

We will close this penultimate chapter, saying that the best equipment of a distillery, after all, is part of the technical staff that counts for its direction, and the enthusiasm and loyalty with which the workers all perform their respective tasks; and from the other side, the vision of the founding house of the company, the ideal in mind, the seal of individuality and purity that they wish to impart to their product, turning it into one of true merit, a source of admiration and pride both inside and outside the country: for both producers and their consumers.


In the new preceding chapters we have tried to give a rough idea, but one that covers in general all aspects of the manufacture of rum. Necessarily much has remained without saying, and much of what has been said will have to be modified, revised or rectified later, as we move forward in the field of our studies on the subject.

We hope that some of our readers interested in the manufacture of rum are decided by an efficient supervision of the process, as well as by introducing improvements and innovations in production aimed at the production of an increasingly better rum. We also believe that any reliable information based on experimental results, and observations obtained in our personal contact with the industry as it is developed on this island, can be exploited, especially by those small producers who, due to lack of resources, find it difficult to employ competent personnel to enter the field of special studies and investigations.

The making of a good rum is not easy; careful study is necessary at every step if we wish permanent success.

The importance that the quality of the crude distillate has, and its influence on the manufacture of commercial rum, are not properly appreciated. It relies too much on the effect of “salsas” or “bases” of aroma and taste. It is also true (and this serves as an excuse for rectifiers-makers of rum) that very few distillates on the market have the natural characteristics of a good raw rum, and there are those that do not even deserve the name of rum. This lack of skill among the distillers to offer a raw product of true quality, obliges the rectifiers-manufacturers to prefer reduced alcohols in the manufacture of their commercial rums. We use the phrase ‘discounted spirits’ not in the strict legal or technical sense, but considering as such, all raw rum distilled at more than 180 degrees test.

We worry that we can not always count on the US market, where our rums currently come under tariff protection. The great advantage that this means tends to make us little careful about the quality of our rums, thinking perhaps that the differences in sales prices will be enough to tilt the balance of the market in our favor. But let us prepare for a change in our political “status”, or a legislature. Restrictive federal regulation can suddenly change this order of things, and then our competition would have to be carried out based on quality, goodness of the product. And to that end we have to prepare. It is necessary to gradually eliminate the “bases” of color, aroma, wood and taste, and to produce better raw distillates. The lack of good raw rums makes our rectifiers-manufacturers have to opt for a mediocre or frankly bad fresh rum, with excessive tufo or produce extremely purified rums, distilled to such a high degree that they prove lacking in the essential bodies needed for a good raw rum.

They prefer these distillates to such high proof grades, without natural aromatic bodies, nor tasting like genuine rum; but at least they lack, at the same time, the insufferable “tufo”, which is so difficult and costly then eliminated. We do not doubt that every liquor rectifier, with true knowledge of its art and of what is good rum, would prefer, if able to find it, a true raw rum as raw material. And this for many reasons, including the large economy that would mean the discontinuation of the excessive use of additives, which, although harmless for the most part, do not stop being an additional expense of importance in the curing of raw rum. In addition, these rums, with a high percentage of foreign matter, tend to create sediments during the time they are not sold in the shop windows of the merchant; which means costly returns sometimes, and more costly business losses in others. There are other good reasons why the liquor rectifier would gladly use a crude distillate without a tufo smell, while having a genuine rum smell and taste; but we lack the time and space to enter deeply into matter.

During the course of this work, we have mentioned several times the aromatic body called rum oil. We believe it is appropriate not to end without first giving some informative information about this valuable constituent of rum, which forms the preponderant factor in the “bouquet” of a genuine rum. This essential oil is a product of the reaction of the medium and the yeast. We doubt that it is as such in the medium or that the yeast exudes it; rather we would say that by means of the pretreatment of the medium we put the material that generates this oil in favorable conditions so that the yeast, acting on this substance directly or indirectly, produces it. Not all the yeasts produce it, nor the same yeast always with the same intensity; for the preparation of the medium is of equal importance that the action of the yeast itself.

During our experiments, we have achieved the production of this aromatic body in varying quantities; but always negligibly. Especially two of our yeasts prove to be good producers of this essential oil when the conditions of the batición are adjusted to achieve that effect.

This essential oil is a colorless liquid, more soluble in alcohol than in water, and highly refractive. Its boiling point is higher than that of alcohol, and volatilizes with some difficulty. The character of its aroma can not be better described than saying that it smells like rum. It does not belong to the family of esters, aldehydes or ketones, because it does not react like any of these chemical compounds when the usual reactions are applied in the identification of them. Rather it presents the characteristics of an essential oil related to terpenes.

The method that has to be used to isolate this essential oil is very painful and complicated, being able to be carried out only by an organic chemist of recognized skill and practice in this kind of work. You must have at your disposal, in addition, a good laboratory, equipped with modern conveniences and necessary equipment for delicate work.

The fact that the boiling point of this essential oil is relatively high explains why in ordinary distillation procedures we do not obtain it in the proportions that we could; It also explains that the use of continuous distillation stills, with a good rectification column, surely means a decrease in the aroma of rum, as regards this essential oil. It also explains why when distilled in an batch distillation still, better rum is obtained. Hence our preference for the batch type.

Neither in the United States nor in Puerto Rico are there methods established by law for rum appreciation. In our humble opinion, the purely chemical analysis offers us very mediocre information, and of very little value in the evaluation of rums of quality. Fractional distillation, accompanied by chemical analysis, is much more valuable. This is very useful, because it makes possible the best separation and graduation of the various volatile materials of the “bouquet” constituting the aroma composed of a rum. If a simple fractional distillation without deflegmation action is used, the limits between the individual constituents of the aroma are not sufficiently defined.

[The last part of this implies that you need a birectifier because it can perform such high reflux]

Complementing the chemical and organoleptic analysis of the rum, with the fractional distillation, and determination of the aroma persistence index by systematic dilution, we could better reach the true assay of a given product. There can be an immense difference between two rums that offer the same chemical analysis, as far as quality is concerned.

When closing this last chapter on rum manufacture we wish to give express thanks to those of our readers who visited us or wrote, during the publication of the articles in the important newspaper “El Mundo”, to offer us a kind word of approval, or ask for an explanation. We would like to express our appreciation to those who suggested the compilation of the articles permanently.

We also wish to express our gratitude to the popular newspaper that published the first and last of these articles, and especially to its worthy and efficient administrator, Mr. Angel Ranos, for the faultless and correct presentation of all the articles published.

Finally, we would like to express our deep appreciation to Mr. Miguel A. Manzano for his intelligent cooperation as assistant chemist in the work of experimentation and translation of German and French literature on the subject; José I. Otero, whose diligence, activity and goodwill this publication has been made possible, and Francisco López Domínguez, who, as Director of this institution, allowed, and kindly encouraged the publication of this circular.


[Arroyo went on to take everything much further and his other papers are collected here. All of his work took a quantum leap when he started using the birectifier which we’ve recently revived.]



11 thoughts on “Circular 106, Rum Manufacture, Rafael Arroyo, 1938

  1. Quote from above:
    “In all those cases in which this initial value is less than pH 5.8 and Beaumé 15-degrees, lime will be added to the mixture, cautiously, in small proportions; taking care to take the pH value of the mixture after each new addition of lime. When a sample thus taken turns out to have a pH value around 5.8 (it can vary more or less a tenth in value) the addition of lime will be suppressed…”

    “In those cases in which the mixture turns out to have a pH greater than 5.8 before being treated, then enough slurry will be added to it to bring the pH value to 6.2; but once this process is finished, the mixture will be treated with enough diluted sulfuric acid to return the pH value 5.8 again.

    [This establishes the pH buffer]”

    “We must also warn that when the moment of adding the lime [to raw cane juice] has arrived, it must be incorporated into the juice until the pH value reaches 7.0; This value is then lowered to 5.8 by the addition of dilute sulfuric acid. From this it can be deduced that the treatment of guarapo is more expensive than that of molasses in the cost of chemical reagents.”

    Been meaning to bring up this question for a while…

    I’m curious if we are entirely clear on the makeup of the “milk of lime”?

    I bring this up because I was under the impression milk of lime was calcium hydroxide. CaOH2 wouldn’t necessarily establish a buffer since it’s such a strong base and the conjugate acid is water and pretty inert. However if he is referring to carbonate salts, that is a different story since carbonate is a medium strength base with a medium strength conjugate acid.

    As suggested in the quotes above (and if he is indeed using CaOH2), he seems to be emphasizing more an amount of calcium to add than an exact pH change. This is exemplified in the case of molasses of various starring pH. And is also suggested by the example with raw sugar as a feedstock, in which the pH is brought all the way to 7 before being returned to 5.8 by sulfuric addition — likely due to lower buffering capacity in cane sugar compared to molasses.

    I wonder if instead of setting up buffer conditions, Arroyo is setting up reaction conditions? Pretreatment could be priming feedstock for rum oil formation either by prepping precursors or maybe even precipitating “bodies” that interfere with essential oil metabolism?

  2. I think it is both buffer and reaction conditions. I’ve read elsewhere in the old literature they thought glycosides were lime decomposable. The buffer may also be absorbing ordinary short chain fatty acids that are a byproduct of fermentation like acetic acid.

    This is a translation and I could have made errors. I’m pretty sure they used nothing but common garden lime. I’m seen info graphics that distinguish the types and I think it was common knowledge how to remove the CO2 from it once it absorbed too much and was not fresh.

    I’m about to start working with it and getting a sense of how it works and behaves physically such as settling and cleaning off surfaces. I’m curious what else comes out of solution (gums) and can be decanted.

    In theory you can generate a portion of rum oil / rose ketones just during molasses prep. You can scale that molasses to 100 ml of absolute alcohol and add 100 ml of absolute alcohol then distill with the birectifier to isolate it. I haven’t done it yet, but I’m getting closer.

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