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FERMENTATION OF MUSTS
Yeasts and microbes in the rhummerie
The importance of the role played by yeasts and bacteria respectively in the rhummerie fermentation, and the interest presented by pure cultures have given rise to long controversies.
As early as 1891, G. Landes, professor of natural history at the Lycée de Saint-Pierre in Martinique, who had studied in the laboratories of France, the technique of bacteriology, advocated the application to the rhummerie of the pure fermentation processes, spread the technique across Europe, and took a patent for an apparatus for the propagation of pure yeasts.
“The use of this apparatus,” he wrote in 1899, “should make it possible to suppress the irregularities of the fermentation, to obtain a tafia of the desired aroma, and to use all the sugar contained in the fermentable molasses, of which an average of 15% was absorbed by accessory fermentations that were often harmful, and I asked the manufacturers to test this device…”
“The test has not been done. Most people listened to my projects with a distracted ear, because they were not aware of the progress made in the way I wanted to push them. Others, better informed, have made the following objections: 1°) You heat your device to sterilize it, you introduce new fuel costs. Will not they absorb the benefits? 2°) By working the molasses as we do, we realize profits that satisfy us. 3°) If one of us uses your device, the others will be obliged to imitate it, and it will be a serious disadvantage of having to transform the tooling. 4°) If you prepare pure yeasts we can carry them in a neighboring island, where, from then on, we will make rum as good as ours. Now, we have the monopoly of preparing good rum and we intend to keep it.”
“The first of these objections was of value from the industrial point of view, but I thought that avoiding the hazards of fermentation and obtaining a rum of a certain aroma should offset fuel costs and experience would have proved it. The other objections were especially valid because they were formulated in an island, and having understood their importance, I postponed my studies on yeast “. (1)
(1) Supplément au Bull. Agr. Martinique, Nov. 1899. 153.
We have reproduced this quotation, a little disgressive, because it translates an insular psychology always flourishing in the West Indies, both English and French.
At about the same time, P. H. Greg, who had studied the chemistry of fermentations in Germany, advised Jamaica on the use of pure yeasts. During researches relating to the nature of the aromatic principles of rum, he had come to the conclusion that the aroma of this eau-de-vie was due mainly to a specific essential oil, which originated by the action of certain yeasts on the cane juice previously defecated with lime. He isolated many yeast from musts, presenting qualities very unequal with regard to the production of the aroma. The most interesting was a top fermenting yeast, No. 18, forming on the surface of liquids, a creamy yellow cap (2).
(2) Yeast has been described as a new species by Jorgensen, under the name Schizosaccharomyces mellacei.
This yeast slowly fermented musts (10-14 days), but caused a strong attenuation and gave a high yield with a very aromatic rum of excellent quality. Greg therefore thought that the use of pure cultures of certain selected yeasts should allow to obtain a rum of more regular and better quality, as well as a higher alcohol yield, and probably to suppress the trash cistern (bagasse tank) , which gives rise to significant losses of sugar.
In the first years of the century, Pairault, senior pharmacist of the colonial troops, after visiting the distilleries of the main rum producing countries of the West Indies and continued for 2 years in the laboratory he settled his research on the manufacture of rum in Saint-Pierre (Martinique), concluding that it is necessary to replace spontaneous fermentations by pure fermentations.
“In summary,” he writes in his work Rum and its manufacture (1903), “using this apparatus (1) for pure fermentations, I could prove that the bacteria did not intervene in the production from the bouquet of normal industrial rum. On the other hand, in these pure fermentations, the loss never exceeded 6 to 7% (instead of 25 to 30 which are usual in Martinique), even with musts of composition of 1/3 more concentrated than in the ordinary.”
(1) Closed cylindrical container with a usable capacity of 500 liters, built by the author to obtain aseptic fermentations.
“Bacteria are therefore only harmful in the fermentation of rum, and there is every interest in getting rid of them or at least reducing their harmful role to a minimum. This is a necessity that is needed today. The vats must no longer be abandoned to the yeasts which chance brings there; the fermentation must take place under the influence of a well-known and pure yeast.”
E. Kayser, director of the Fermentation Laboratory at the Institut Pasteur in Paris, carried out a detailed study in 1913 of rum yeasts and the factors involved in rhummerie fermentation. After having noted the complexity of this one, and recognized the influence exerted on the composition of the distillate by the species and the race of the ferments (including the microbes, which increase the rate of the impurities), the composition of the medium, etc., he also recommend the use of selected yeasts. The choice of the ferments should not be limited to the yeasts of culture (Saccharomyces and Shizosaccharomyces), but could extend to the veil yeasts (Torula), to the mushrooms in yeast form, etc., and to include the association of several yeasts. Kayser writes:
“The race of yeast (bottom fermenting yeast, schizosaccharomyces, veil yeast), the manner of applying it, the composition of the medium (addition of nitrogenous matter, acid, bisulfite K, phosphate Mn, fluoride, etc.), the duration and the purity of fermentation, all factors that influence the composition of the distilled product. It is therefore important to make a judicious choice of yeast, to know its properties, its nitrogenous food requirements, its acidity and its optimum temperature, while taking into account the taste of the customers…”
“When one observes these various precautions, it will be seen that the use of yeasts selected in the rhummerie will lead to enormous benefits, significant reduction in the duration of fermentation, better yields, products of constant composition, etc …”
“There is no doubt that the selected yeasts will be more and more applied in rhummerie and the day, perhaps not too far, where a large rhummerie sterilize its musts, seeds them with selected yeasts, judiciously chosen for a specific purpose, the composition of the rum will be able to change according to the desire of the industrialist”.
Bettinger, after having studied the use of yeasts selected in Martinique under the conditions of industrial practice, also advises the application of pure fermentation methods, but preferring a mixture of yeast races isolated from canes of the region.
He concludes from his experiences:
“This shows that the pace of the fermentation was very fast, and the work thus started gave us remarkable yields, since the increase resulting from the replacement of the work by spontaneous yeast, by the work in pure yeasts, has largely exceeded the 20% which had been announced, all before an absolute regularity in the fermentations. With the aroma question, we were able to vary the impurity rate according to the proportion of different yeasts and the quality (acidity more or less) of the vinasse… One realizes how easy it is to vary the impurities and to obtain a good rum while increasing the yield, this by working only with pure cultures, without changing any other conditions of work “.
In opposition to the previous authors, the chemists who had to study the manufacture of Rum in Jamaica generally agree to attribute to the bacteria an important part, if not predominant, in the formation of the bouquet of the grand arôme rums.
Allan (1905), a fermentation specialist at the Jamaica Experimental Station, considers that this bouquet is mainly due to esters (acetic, butyric, etc.), the production of which is mainly the work of bacteria. The variety of microorganisms and the complexity of the reactions involved in the production of Jamaican type rums make it impossible to apply pure fermentation methods.
“The characteristic properties of Jamaican rum,” he writes, “come from sugary liquids rich in albuminoids and fermented by yeasts and bacteria. If we accept that the essential difference between rum and grand arôme rum is in the level of esters, we must conclude that this difference is due to the method of manufacture, which strongly favors the development and the action of the bacteria producing acid, which, by combining with alcohol, give rise to aromatic esters…”
“Mixed organisms often produce very different products than they produce in pure culture. There may be interaction between the products of the fermentation and completely new substances are likely to appear. We must not lose sight of this function of mixed cultures, when we want to obtain a particular bouquet by means of pure cultures. It is almost certain in fact that we can only approximate, with the help of pure cultures, the special rum bouquet I currently produce… Complete scientific control with the use of pure culture methods can not be envisaged, but an empirical control, based on scientific data and inspired by the one used in English distilleries, should be applied in the production of rum in order to standardize quality and reduce losses to a minimum.”
Ashby, who succeeded Allan in 1907, also admits that the characteristic fragrance of Jamaican rum is due to high molecular weight fatty acid esters (caprylic, capric, lauric acids). Although he tends to give more importance to yeasts, mainly to Schizosaccharomyces, as aroma producers, he nevertheless recognizes the important role played by microbes, especially during preliminary fermentation affecting the skimmings, the acid and aroma in bagasse tanks. [Acid here refers to the cane vinegar and aroma here refers to muck.]
Cousins, chemist at the Department of Agriculture, wrote at the same time, about moderately full-bodied rums for export to England:
“These rums are distinguished by their full-bodied character, mainly from high molecular weight esters of acids. These acids are not formed from sugars; they are almost completely lacking in rums other than those of Jamaica, which are supplied by molasses diluted with water without vinasse or acid-skimmings, and distillates in high-grade columns. Our research has shown that these acids come from the bacterial decomposition of dead yeasts found in distillery liquids in Jamaica. I have come to the conclusion that the yeasts that remain in the old hollow cisterns in the soil are for a great significance in the formation of the delicate aroma that many rums destined for metropolitan commerce possess.”
J. Guillaume, head of manufacturing at the Galion plant (Martinique), also concludes from the experience he has of the production of grand arôme rum, the essential role of bacteria. “We are,” he says, “neither in the opinion of Pairault, who denies the intervention of bacteria in the production of the bouquet of rums, nor the opinion of Kayser and Bettinger, who advise the use of pure yeasts for the production of rums. We believe, on the contrary, that bacteria play a leading role in the production of the characteristic ethers of rum”.
Ficker and Szügs, who studied cane molasses fermentation in Brazil, found the presence of acetic, butyric and lactic bacteria in musts conducted by spontaneous fermentation. On the other hand, by seeding a sterilized molasses must with budding and fission yeasts, alone or associated with acetic and butyric ferments, they observed that the yeasts alone gave a neutral brandy, without characteristic aroma. Association of yeasts with acetic bacteria allowed them to have a more aromatic product with the pleasant perfume of ethyl acetate. By use of butyric ferments, one obtained a rum of pleasant fruity aroma. But it was only by combining both acetic and butyric bacteria with yeasts that we had a very characteristic, intense and persistent rum eau-de-vie. Budding yeasts, although isolated from cane, were less interesting than those with fission (Pombé yeast and an isolated fission yeast from cocoa pods). The latter helped to give the rum a franker and more intense aroma. By adding to the must, in place of the bacteria, pure acetic acid and butyric acid, a mediocre product with a pronounced butyric odor was obtained. [I think the sensory description of this very last part implies that no rum oil was produced and the radiant phenomenon was not observed so the butryic acid was left sticking out like a sore thumb.]
The authors conclude accordingly: “The aroma of rum does not result from the action of yeasts, but comes, for the most part, from the intervention of acetic, butyric and perhaps lactic bacteria, associated with yeasts, particularly to fission yeasts.
Finally, from 1918, the distillers of the French West Indies, eager to increase alcohol yield, wanted to implement the recommendations of Pairault and Kayser on pure fermentations. The musts were, if not sterilized, at least supplemented with sulfuric acid and, in certain cases, with fluorides. Yeast propogation appliances were used and pure yeasts were imported from the metropolis.
The results obtained were much less satisfactory than expected. If the yields were improved, the quality of the product was significantly reduced. Receiving rums more and more neutral, no longer corresponding to the taste of the customers, the merchants of the Metropole, gave a cry of alarm. X. Rocques, commissioned by the Ministry of Agriculture to investigate the specific characteristics of rums in the French colonies, concluded as follows the many analyzes he carried out in 1925-26:
“The rums produced today are generally characterized by their low acid and ethers content and relatively high content of higher alcohols, and their nonalcoholic ratio is generally low. These characters are the opposite of those encountered in the composition of ancient rums, which were rich in acids, ethers, low in higher alcohols and high non-alcoholic content. These differences come, in my opinion, only from fermentations, unique in their speed and purity.”
In another article, the same author wrote: “Producers of rum, by improving their manufacture and by introducing scientific methods, obtain spirits much purer than those produced previously, but one wonders if they have not exceeded the goal which it was desirable to achieve, by preserving the organoleptic characteristics enjoyed by the consumers with the eau-de-vie obtained”.
Since then, rum producers in Martinique have, for the most part, given up the use of selected yeasts. The yeast propogation appliances were scrapped. The rums obtained are considered on the French market as much higher quality than those of Guadeloupe, where the methods of pure fermentation have been maintained, and benefit from them an interesting added value. Many distillers have, therefore, concluded to the superiority of the spontaneous fermentation processes, which make it possible to obtain a more full-bodied, more intense and more characteristic bouquet.
As rightly pointed out by Arroyo, the differences of opinion and controversies above are due to misunderstandings and hasty generalizations.
First, it appears to be well demonstrated that bacteria, as well as wild yeasts and yeasts-mildew [moississures], play a very important role in some rum fermentations. This is particularly so in the manufacture of grand arôme rums and medium-bodied rums with relatively slow fermentation. On the other hand, the action of these microorganisms is weak or nil in the case of light rums, obtained by rapid fermentation, in which budding yeasts are involved exclusively or almost exclusively. [The mildew yeasts may refer to Arroyo’s Suaveolens or to others that were previously thought to be molds but are now considered alt-yeasts.]
In the latter case, the selected yeasts can be used to advantage, “We can not overemphasize,” says Arroyo, “that the bouquet and aroma of certain types of rum are reinforced by bacteria, however these are not essential for making good rum. In fact, in the case of certain light and very delicate perfumes, which are very popular today, the intervention of bacteria during fermentation is undesirable and harmful.” Practically speaking, many rhummeries producing rums with little body, have implemented the processes of pure fermentation, especially in Cuba, Guadeloupe, etc. The failures that may have been experienced are most often due to the fact that the yeasts have not been judiciously chosen.
The question is more delicate for the grand arôme rums. The diversity of organisms and the complexity of the biochemical reactions that occur in the conditions of industrial practice seem to make a priori the use of pure ferments very difficult. This, however, would not be impossible, according to Arroyo, provided that it is not limited to Saccharomyces or Shizosaccharomyces, but to associate with them bacteria and possibly other ferments (molds, yeasts, etc.), selected and multiplied aseptically. The author claims to have succeeded in obtaining Jamaican-style grand arôme rums by carrying out the fermentation by means of symbiosis between Schizosaccharomyce Pombe – Clostridium saccharo-butyricum. Instead of 10-15 days in the process of Jamaica, the duration of the fermentation was reduced to 2-3 days.
Be that as it may, the application of pure fermentation methods, especially when it is proposed to obtain a relatively full-bodied rum, requires preliminary studies relating to the selection of yeasts, the composition of musts, etc. as well as a rigorous chemical and biological control of manufacturing. Wanting, as is so often done in rhymes, to perform aseptic fermentations without the presence of a chemist savvy, is exposing himself to serious setbacks.
[not sure if this should be translated but implies a yeast starter]
Leaven is generally called a medium in which the yeast must multiply and acclimatize before being introduced into the musts. In a narrower sense, the term refers to a medium prepared with different elements of the fermenting must, as opposed to a pied de cuve, which is sometimes applied to a culture medium made of the must itself. [pied de cuve is either a yeast footing or an experimental selection technique using the must itself.]
Until recently, the fermentation of rhummerie musts was generally done by spontaneous seeding. It was only in the beginning, the start-up of the distillery or in certain special productions, like that of Arak from Batavia, that leavens were prepared. Today, although the spontaneous seeding of musts is still commonly practiced, natural yeasts, mixtures of yeasts prepared from cane or molasses, and leavens of pure yeast, obtained with a single cell, tend, however, to be used more and more, especially in the manufacture of light rums. In the beet molasses distillery and that of starchy materials, the use of leavens is indispensable.
In English Guiana and Jamaica, rum fermentations are always by spontaneous seeding. In the first country, the development of foreign organisms (microbes, wild yeasts, etc.) is prevented by the addition to the must of an antiseptic (usually sulfuric acid). In Jamaica, on the other hand, the proliferation of these organisms is encouraged by special methods (prolongation of the fermentation, maceration of certain elements of the must in the presence of bagasse, etc.). [vinegar process]
In the French West Indies, particularly in Martinique, and in the agricultural rhummeries used for raw vesou, spontaneous fermentation, without the use of leavens, is also often practiced. It is the same in Réunion. In these colonies, as in English Guiana, the development of foreign ferments is controlled by the addition of sulfuric acid to the must.
As we have already indicated, the vesou always brings yeast, from the sugar cane on which it exists, along with all kinds of other germs (bacteria, mold, wild yeasts). The fermentation consequently begins well and continues rapidly (2-3 days in general).
Molasses, if not worked immediately, also contains yeasts from the dust of the air. The beginning of the fermentation, at the beginning of the season, is sometimes difficult. But thereafter, the yeast remaining on the walls of the tanks allows to obtain a fairly fast fermentation. This speed is obviously a function of the quantity of yeast available. It will be larger, all things being equal, in the smaller than in the large vats, in the wooden vats than in the sheet-metal vats and in the old vats than in the new vats.
Pairault attributes the preference granted in the old industrial distilleries of St-Pierre Martinique) to the small vats (700 to 1,200 l.), to the fact that these, having more yeast available on their walls with respect to the same mass of liquid that large capacity tanks fermented faster and often gave better yield. It is for an analogous reason that the vats are very summarily cleaned, by washing with a few drops of water, after the fermentation of the fermented must.
The duration of the fermentation of a normal molasses must is generally 6 days. However, it can be lowered (especially in English Guiana at 2-3 days, or in some cases at 8-10 days) and the musts of cooked vesous and battery syrup, which have been rendered sterile during the defecation and concentration of the juice, ferment very slowly if they are not seeded. The duration of the fermentation is a week.
Spontaneous fermentation has the advantage of giving rums that are more full-bodied and more aromatic than the rapid fermentations obtained by seeding with pure leavens. Thus, molasses rums produced in Martinique at the beginning of the century, when spontaneous fermentations were the rule, generally measured 400 to 600 impurities per hl. of pure alcohol (Zizine), with an ester level of 100 – 200, while today in Guadeloupe, where seeding and cutting are commonly practiced, the impurity coefficient has fallen to 200 – 350 and the level of esters at 30 – 60. [Cutting here probably refers back slopping.]
Unfortunately, this method of work has serious drawbacks. The fermentations are long, which requires having a large fermenting room, and is often irregular. Fermentation accidents, especially acetic infection, are to be feared. The quality of the eau-de-vie is variable, the equilibrium state that exists between the different ferments being likely to be easily modified. It is a well-known fact in the French West Indies that the rum of vesou produced in a given distillery easily varies from one year to the next, and even during a season, without any modification being made to the manufacturing technique. Last but not least, the alcohol yield is usually very poor.
Pairault, for example, indicates as average yields obtained in the molasses distilleries of Martinique at the end of the last century, 75 to 80% of the theoretical figure (Pasteur coefficient), but these yields were very variable from one distillery to the other. By working with pure yeasts, this author was able to obtain at least 20% more output than ordinary yields. Tumang (1) reports having achieved at a molasses distillery in Brazil, the average yield of 40.03 l. at 50.52 l. of alcohol per 100 kg of total sugars, by replacing spontaneous fermentation with pure yeasts, but without sterilization of the musts.
(1) Sugar News XIII, 276, 1932.
The use of natural leavens has been practiced for a long time, to obtain the beginning of the fermentation at the beginning of the season.
Charpentier de Cossigny wrote at the beginning of the nineteenth century. “In the experiments I made on the manufacture of sugar spirits, I recognized that the liquors contained in the vats or barrels did not have a degree of simultaneous fermentation; whence it follows that such parts of the substances which are dissolved there ferment before the others, and that the former have already passed the spirit degree, and have reached the acid state [gone to vinegar!], which furnishes no ardent spirit; while the second ones having entered fermentation only after those, have not yet the degree suitable for the distillation. It is necessary, therefore, to employ the means which art can suggest to approach as closely as possible the degree of simultaneity. To achieve this goal, I advise to stir often the liquor which is in fermentation, and to add a leaven which accelerates it. I will indicate several ferments which will fill the object that I have in sight:
“1 °) We will leave in the tank that has just distilled a little grappe (this is what we call the liquor that is in fermentation), and we will mix with the new grappe, stirring the mixture many times;
2°) More canes can be cut than are needed to fill the vat; they will be kept exposed to the air, and even to the sun, if they are in a hurry; they will be expressed after a few days, and their juice will be poured into the vat containing the grappe;”
3 °) We will put vesou in boilers which will be maintained a little tepid: when the fermentation will be in full activity, one will pour them in the vat … ”
Ducœurjoly, in Santo Domingo, indicates the preparation of a special leaven, used at the beginning of the season, “This leaven is composed,” he writes, “with the bagasses which falls, in very small strands, from the bucket of the mill on the the ground that surrounds them.They are thrown into barrels, where their fermentable qualities develop; the proportions are 5 tubs, 5 gallons each, for a 100-gallon piece, which is then filled with water; this mixture is agitated with a stirring-pot at least three times, and even more often if it is possible, over twenty-four hours; after 30 hours the fermentation begins to settle there. The clear liquor, drawn off by a tap placed at the bottom of the tank was used in the preparation of musts, at the rate of 10% of the volume thereof.”
Porter (1830) reports that some distillers soaked woolen cloths in the scums collected on the surface of musts, dried them carefully, and kept them for introduction into the vats early in the next season.
“It often happens,” writes Payen (2), “that the fermentation is activated, at the same time as the quality of the product is improved, by adding to the dissolution of the molasses the juice obtained, using pressings of cane more or less altered or started on a footing by the rats’ teeth.” [SOS it may be great to have this translation firmed up. The infamous rum canes…]
(2) Traité complet de la distillation, 2 Ed, Paris, 1861.
The mode of preparation of natural leavens is quite variable. Often it is sufficient to take vesou that is kept at a moderate temperature, sometimes in the presence of bagasse, and once the liquid in full fermentation, it is introduced into the tanks.
Sometimes you add fruit juices and various other ingredients to the vesou. In the little rhummeries of Brazil, for example, the leaven would be prepared as follows, according to Godoy: We take 50 – 60 liters of cane juice, to which are added sour oranges, corn bran, straw, etc., and bring the mixture near the fire, so that it enters fermentation more quickly. The prepared ferment is sent to the first vat, which will then provide the leaven required for subsequent vats.
Denys reports that in the small distilleries of South America working the battery syrup, a good amount of sour oranges or lemons, sometimes some grilled corn is added to the must, to start the first tank. Sour oranges have the advantage of providing both acidity and a very pure yeast.
At the end of the last century, the following process was often applied to molasses distilleries in Martinique. At the beginning of the season, the first leaven was obtained by macerating bagasse in must. Thereafter, the foam collected on the surface of the musts in fermentation was placed in a receptacle placed next to the vats, and 5% of the fresh molasses was added. After about a day, once the density had fallen by half, the leaven was added to the vats just filled. During the rum season, the leaven was constantly fed with new scums. Despite the seeding, fermentation was slow (5-6 days in general), this being probably due to the fact that the leaven thus prepared consisted mainly of top fermenting fission yeasts, that were not very active. [We have collected a lot of data points to update and adapt this technique.]
It should also be noted that the defecation foam [skimmings], once used in rhumming and still used in Jamaica, is a powerful source of natural leavening, especially when it is subjected to a preliminary fermentation before being included in the composition of musts. [We see an explanation by Kervegant very early on in the text why skimmings went away when molasses processing changed. Vinegar production replaced skimmings and may sitll be a significant source of yeast not well acknowledged by distillers.]
De Sornay describes the process for the preparation of starters used in Mauritius as follows: “A small barrel of 15 to 20 liters, filled with molasses solution at 10° Baumé, is exposed to the air to allow ferments which are there to develop. We sometimes add some oats and bottoms of Porter bottles. The fermentation established, the practitioner in charge increases the volume of the fermented liquid, by transferring it into a barrel of 200 l. and constantly adding new unboiled liquid at 10° Baumé. In general, 24 h. after the last charge, the fermentation is in full activity; he then sends it to the two fermenting bins, where beforehand he has the syrup diluted to the desired degree, 10° B. Some distillers, however, prefer first to seed one of the tanks, then, when in full fermentation, to pour a certain amount into the other. After 18 hours the mass is already at 4 or 5 ° B, they then let the fermented liquid flow into the vats where the mass is brewed. The quantum of yeast they deem essential is usually 2 tanks for 4 tanks, and the 2 tanks are not empty entirely since they reserve a part as a pied de cuve, that they increase and prepare for the next morning. After a fortnight when yields begin to fall, they renew their ferment, as we said above. [Interesting to see they are very much aware their yields are falling like as bacteria take hold.]
“It is good, however, to indicate a modus operandi quite different from the one we have just described. Some distillers, from the beginning, after having obtained a mass fermented by syrups of 10° B, increase the concentration to 18, 19 and even sometimes 20° B, so as to partially prevent the fall of the degree. They paralyze the action of the ferment, and the more it is perennial the more they increase the density of the syrup by incorporating less water. They increase as usual their volume and transfer into the 2 tanks always at 20° B. The next day, when they seed the large vats, the degree of the fermented liquid is often less than 10 or 12° Baumé. [I have this feeling that in the great 1840’s Mark Twain style distill off between W.F. Whitehouse and the young Irish interlopers, something like these last two ideas would be the dueling techniques.]
Ragi, or Javanese leaven, used in the manufacture of Arak from Batavia, is the object of a very special preparation, which we will examine in another chapter.
Nowadays, we often prepare natural leavens purified from cane juice. The vesou obtained by crushing canes is supplemented with an antiseptic (e.g. sulfuric acid) and left to spontaneous fermentation. Once finished, the yeast sediment is used to ferment anew sterile fresh cane juice in the presence of antiseptic. The process is repeated several times, until the disappearance of bacteria, so as to have a mixture of pure yeasts which, together, have properties that can not be found in isolated breeds. The subsequent propagation of starters is done by ordinary methods.
This process was used at the Santa Therezinha distillery in Pernambuco, Brazil, with great success. The starters obtained had exceptional vigor and could be used for an average period of 25 days without renewal. The alcohol yield of molasses must at 21-22 ° Brix was 9.42% (Lebedeff) (1). These leavens unfortunately often have the disadvantage of giving a rum too neutral and insufficiently aromatic.
(1) Arch. Inst. Pesq. Agron. 1, 74, 1938.
Leavens of pure yeast.
Pure yeast leavens are quite commonly used in some countries (Cuba, United States, Guadeloupe, etc.) for the production of light rums. Their use in rum production, especially if one wants to obtain a full-bodied product, must be done with great discretion and after having been meticulously studied the characteristics of the chosen yeast by laboratory experiments and semi-industrial tests.
Selection of yeasts. – Kayser, Bettinger and especially Arroyo rightly insist on the paramount importance of choosing the yeast race.
“Our experiences have shown us,” writes Arroyo, “that the factors involved in making quality rum are many and varied, but none plays a role as important as the judicious selection of the yeast breed most appropriate to the characteristics desired to be realized in the finished product. A yeast capable of provoking the fermentation of cane juice or molasses is not necessarily a rum yeast. It is for lack of recognizing the importance of this basic principle that we have often been led to produce rum of inferior quality”.
According to the same author, rum yeasts can be isolated either from the skin of the cane itself or from products obtained during the manufacture of sugar (molasses, scums). The important point is to choose a breed well suited to the type of rum you want to make. In general, bottom fermenting budding yeasts are more suitable for light rums, whereas in the case of grand arôme rums, top fermenting yeasts with scissiparity [fission] give better results. But to have precise information, it will be necessary to resort to the direct experimentation; after having isolated several races of yeast, they will be tested at the factory, so as to obtain a perfectly satisfactory race.
It may also be advantageous to use, in certain cases, yeasts having a different origin than the cane or its products. Thus Ficker and Szügs in Brazil and Arroyo himself in Puerto Rico have achieved good results with schizosaccharomyces Pombe. Some rums from the French West Indies or from Cuba of excellent quality are produced using wine yeasts. Most often, however, the eaux-de-vies thus produced no longer have the typical bouquet of rum, or this bouquet is very attenuated. We were able to appreciate the delicacy of certain rums of vesou from Martinique, whose aroma reminded us of the eau-de-vie of Marc or Cognac. But it was no longer strictly rum, in the sense of gourmets. The eaux-de-vie de canne is well accepted in the local market or even in some foreign markets (USA), where they are used mainly for making cocktails. On the other hand, they are not suitable for export to Europe, where a strong, well-characterized rum bouquet product is required for the preparation of hot grogs and punches. In France, in particular, there is a tendency to consider them as lower substitutes for wine or marc spirits.
According to Arroyo, a rum yeast must fulfill the following conditions: to give a good alcoholic yield in a reasonable period of time (24 to 48 hours from seeing): b) to obtain a distillate of well-balanced chemical composition, rich in rum oil, with the characteristic taste, body and aroma of rum; c) produce a rum capable of acquiring the appropriate degree of maturity in a relatively short time, ie after 6 to 12 months of aging.
Other important points to consider are: the ability of yeast to withstand high fermentation temperatures, resistance to relatively high alcohol concentrations in the medium and, in the case of heavy rums, tolerance of the yeast to fatty acids that exist in the must in relatively high proportions.
The selection of yeasts is therefore a complex operation, which involves many tests and analyzes to make it possible to realize whether a given race has the desired properties. Arroyo has found that the different races which he has examined show, with regard to the realization of the conditions indicated above, a great variability, and that it is very difficult to find the ideal yeast which satisfactorily fills them all.
Although less important, according to Arroyo, than the race of the yeast, the composition of the must, especially with regard to the density, the acidity and the pre-treatment of the raw material, however plays a big role in getting a quality rum, aging rapidly. This composition must be carefully adjusted to the requirements of the yeast race used, if it is to achieve its full potential for producing an aromatic rum.
The combination of several yeasts, of different properties, appears likely to facilitate in some cases the manufacture of the type of eau-de-vie sought.
Vandevelde (1) concludes the work he has done on the symbiosis of yeasts, that mixtures of breeds give, in fermentation industries far better results than the use of a single yeast. Similar findings have been made in wine making and cider making (Müller-Thurgau, Kayser), as well as in rhummeries (Kayser, Arroyo). But the difficulty is to determine the mixtures that allow the establishment of a stable equilibrium and then the equilibrium state that corresponds to the production of a quality brandy.
(1) Rev. Gen. Chim. XVIII, 88, 1915.
Cases of natural balance or symbiosis have been reported on several occasions. Thus Will cites the example of two different races of yeast, which have been maintained for 12 years, without appreciable modification of their individual characteristics, in a brewery leaven. Van Laer also noted the case of a brewery fermentation starter, in which a yeast of the cerevisiae type, a torula and, in lesser proportion, two yeasts of the pastorianus type developed in symbiosis. As examples of symbiosis between yeasts and microbes, one can point out; the fermentation of the “tiby”, an alcoholic beverage from Mexico, caused by the combination of Saccharomyces Radaisii and Bacillus mexicanus (Lutz); the fermentation of the fermented “leben” of Egypt, due to two yeasts, Saccharomycee lebenis and Mycoderma lebens, and to a bacterium, Streptococcus lebenis (Rist and Khoury). [tiby may be a reference to the 1906 Journal of Mycology.]
Such associations, however, are exceptional. When pure yeast mixtures are used in the fermentation industries, it is rare that a stable equilibrium is established between them; one of the races almost always predominates over the others. On the other hand, some associations give poor results; this is particularly the case of the mixture of active yeasts with the varieties Pombé, Logos, Frohber. The associations Pombe-Logos, Pombe-race XII (of Berlin) gave to Komarowa (1) the best yields in alcohol, in the fermentation of musts of potatoes.
(1) Mikrobiologija VI, 1067, 1937.
Practically, because of the uncertainty of our knowledge on the development of the various mixed yeasts, it is most often required either to renew the leavens very frequently, or to propagate the breeds separately and to mix them at the time of seeding the musts.
Arroyo, in Puerto Rico, has obtained interesting results by using, for the fermentation of molasses and vesou musts, pure yeasts in association with bacteria (Clostridium saccharo-butyricum, Propionobacterium technicum) or yeast-shaped fungi. (Oidium suaveolens).
He has developed the following process, in the manufacture of a grand arôme rum of the Jamaica type, by using, for the fermentation of cane molasses, acid-resistant yeasts (in particular of race no. 501, belonging to the genus Schizosaccharomyces) in symbiosis with the butyric bacterium Clostridium saccharo-butyricum.
Molasses, after having been purified and sterilized, as previously indicated in the “Pretreatment of musts” (Arroyo process), is diluted to contain a sugar content close to, but less than 13%. The acidity of the must, as well as that of the pied de cuve [footing], are adjusted, so that the pH is between 5.5 and 5.8. The fermentation is carried out in a closed metal tank, equipped with a refrigeration system and a device to ensure the stirring of the liquid (mechanical stirrer or system of carbon dioxide agitation, avoiding the injection of air which thwarts the development of anaerobic bacteria). It is also necessary to equip the tank with the necessary apparatus for the recording of temperature and pH.
The leaven is first introduced into the vat (10% of the volume of the must), then the must is poured, with gentle stirring, so as to ensure a uniform distribution of the yeast. When the tank is filled, the pH is read and adjusted, if necessary, to a value between 5.5 and 5.8 by the addition of sulfuric acid or milk of lime. The temperature, from 30-32 ° C at the beginning, is maintained during the fermentation between 30 and 33 ° (the rum obtained at higher temperatures is of less good quality).
Six hours after the start of the fermentation, we take samples, renewed every 2 hours to determine the amount of sugar and alcohol in the must. When the volume of alcohol is about 3.5 to 4.0% and that of total sugars per 100 cc. must has fallen below 60 gr., the leaven of bacteria is added, after having brought back, if necessary, the pH to 5.5-5.8. By gently stirring, this leaven is introduced into the tank in the proportion of about 2% of the volume of the liquid in fermentation. The higher the ratio of the number of bacteria to that of yeasts, the more the rum is full-bodied. But if this ratio significantly exceeds 1.5 (ie 2% of bacterial starter for 10% yeast leaven), it is likely to obtain low yields of alcohol, and too rapid multiplication of the bacterium limiting or stopping the development and zymatic action of the yeast.
It is for the same reason that the temperature must be carefully maintained, after addition of the bacterium, at about 29-30 °C. The pH also needs to be controlled so that it does not fall below 5.0; when it falls to 4.0, the bacterium loses activity and sporulates. Fermentation is usually complete after 36 to 48 hours.
The table below gives some of the results obtained in the fermentation of cane molasses by yeast 501 alone (a) and the same yeast in symbiosis with B. saccharo-butyricum (b):
In the presence of B. saccharo-butyricum, the duration of the fermentation is considerably reduced, which seems to be due mainly to the emission by the bacterium of mitogenetic radiations, which increase the speed of multiplication and the zymogenic power of the yeast. In addition, the level of the esters, the aroma and the bouquet of the rum are substantially increased. The eau-de-vie also ages faster. On the other hand, there are no significant differences as regards the alcohol yield or the residual sugars of the must. [Here Kervegant is only parroting Arroyo and as exciting as it sounds, this may never have been achieved at commercial scale.]
Arroyo also used an imperfect fungus, Oidium suaveolens, to make full-bodied rums of vesou. This ferment, which has little action on sugars, but produces aromatic esters with an apple odor from the proteic matters of the must, has been used in two different ways:
(a) A sterilized cane juice juice containing 12 to 15% sugar was inoculated with the Oidium culture, 24 to 72 hours after the film of powdery mildew formed on the surface of the liquid, the yeast leaven (No. 764) was introduced and the fermentation allowed to continue under the usual conditions;
b) The must was first fermented and the powdery mildew was introduced towards the end of the alcoholic fermentation.
Both methods worked satisfactorily, but the rum provided by the first had a more intense aroma and flavor. Here after are some of the results obtained by the author (1-4 first method – 7-10 2nd method):
Acclimation of yeasts. — It is often advisable to acclimatize the yeasts to the special conditions in which they must carry out the fermentation, especially at high temperatures and antiseptics. In the tropical distillery, acclimation to high temperatures, useful in the case of yeasts in hot countries, may be indispensable for those from temperate regions. [This refers to using yeasts from temperate locals such as winery yeasts, but the current challenge with Pombe is figuring out how to acclimate it to temperate climates.]
Chaturvedi advises to operate in the following way. A must is prepared at 20 ° Brix, with malt extract and molasses by half, and diluted with a quarter of its volume of pineapple juice freshly pressed (1). Yeast is added and incubated at 32-34 ° for 24 hours. The operation is repeated on the yeast for about 10 generations. The author has found that the ferment power decreases considerably in the first generations, but as acclimation occurs, the yeast regains its strength and may even eventually show greater efficiency than originally. He was thus able to accustom selected races in the temperate regions to withstand relatively high temperatures and alcohol concentrations. [Fascinating!]
(1) Eoff and his collaborators have also observed that wine yeast grown in a medium containing fresh pineapple juice acquired the property of better tolerating high doses of alcohol. [This seems a little wacky, but there may be something to it!]
When hydrofluoric acid or florines are added to musts, it is advisable to acclimate the yeast beforehand to these antiseptics. In order to increase the fermentable power of the latter, it is necessary to prepare leavens containing a dose of hydrofluoric acid double that of the must. Starting from a non-acclimated yeast, it will be possible, in a first operation, to introduce 7.5 gr. of antiseptic per hl. in the leaven and 4 gr. in the must: in a second operation, 10 gr. and 5 gr .; in a third 15 gr. and 7.5 gr., and so on.
Preparation of starters [levains] (2).
(2) Levy (L.) – Microbes et distillerie. Paris, 1900.
The characteristic of a good leaven is not only to produce many cells, but also to give an adult population having completed its growth, without, however, having begun the fermentation, which must take place only at the expense of the must itself. The release of carbonic acid and the production of alcohol must therefore be weak. [This is very much easier said than done. True aerobic growth is hard to achieve.]
The degree of multiplication obtained in a leaven is rather low: from 4 or 5 in the case of rich leavens, it falls to 2 or 3 in that of poor leavens. It depends on the composition of the must, the temperature, and especially the aeration. The sugar concentration does not affect the amount of yeast formed unless it is very strong. On the other hand, this increases with the nitrogen content of the must, up to a certain limit, which depends on the sugar content and the temperature. The nitrogen content of the yeast also increases in the same direction, up to 0.5% nitrogen in the yeast. The yeast having a fermentable power all the greater as it is more nitrogenous, it is advantageous for musts to be rich in nitrogenous matter, unless one wants to have a very rapid fermentation (yeasts with a high nitrogen content are more lazy than others). In Europe, rich leavens (green malt leavens) usually measure 20% sugar and 0.5% nitrogen, and poor leavens 6-8% sugar and 0.15-0.25% nitrogen.
With regard to the influence of temperature, Pedersen found that the first day the maximum increase occurred at 30°, the second day at 13°, but that after 8 days, the total increase was the same whatever the temperature. With starters that ferment in less than 24 hours, relatively high temperatures are therefore advantageous.
Pasteur has shown that to obtain a high multiplication of the yeast, it was necessary to aerate it energetically. The aeration can be carried out by subjecting the yeast to repeated sieving by pouring it several times in succession from one container into the other or by beating it with a metal whisk. But it is still preferable, to avoid contamination, to inject in air for the starter, sterilized by filtration on salicylated cotton or by bubbling in sulfuric acid to 1/5.
The period of increase, or time necessary to obtain the maximum multiplication of the yeast, is all the shorter if the seeding has been more abundant and the temperature higher at the beginning. Nevertheless, if this elevation is too high, the fermentation begins too early; the period of fermentation encroaching on that of growth, cell multiplication and longevity are diminished. If there is interest in having a short growth period, it is important that it be done entirely [in the starter?]. It is also preferable to go slightly beyond the end of the period than to not reach it, for if, in the first case, we obtain cells slightly affected by the alcohol which has been formed, in the second we have young cells which lack activity in their subsequent multiplication and resist poorly to foreign ferments. [This paragraph deserves some attention contextualizing.]
In Europe, in the case of the starter used for the fermentation of beet juice and beet molasses, the leaven is used, when its density is 0.004, i.e. about 1 ° Brix, above the fall density [density of the final must?]. Nitrogen enriched leavens are used as soon as the density has fallen by half, the more nutritious medium accelerating the growth period and advancing the fermentation period. In hot countries, where the fermentation period is hindered by the rise in temperature, it will also be important to use the starter and leaven when their density is reduced by half. Rather than relying on the empirical characteristics of the maturity of starters, it is better to follow the development of cells under a microscope.
In beet juice and beet molasses distilleries, and especially in those of starchy materials (grains, potatoes), very commonly leavens are used, that is to say, formed with elements different from those of the must ; malt levains, levains of soured grains. In the rhummery, on the other hand, except in certain particular cases (manufacture of Batavia’s arak for example), only vats prepared with juice (1) or cane molasses are used.
(1) A must of cane juice for the fermentation of molasses may, however, be regarded as leaven, rather than as a pied de cuve. [The leaven as reinforced here may refer to the smallest batches growing up from a slant, while the pied de cuve is more like the starter or footing before the final must.]
These musts, often deficient in nitrogen and in phosphoric acid, are better enriched by the addition of nitrogenous matter (Am sulphate, peptonised yeast) and possibly soluble phosphates. Their acidity, adjusted by means of vinasse or sulfuric acid, must be a little weaker than that of the liquid to be fermented.
Barbet recommends enriching the musts of cane molasses by adding a small amount of acid-sacrificed corn, neutralized and filtered, or a little maltopeptone.
In the Magne method, which is very much used in the United States, molasses leaven is added with sulfuric acid and Am. sulphate. Freeland gives the following information on the composition of the different environments:
The intermediate mother tank is sometimes removed, the leaven from the pure culture apparatus (which then must have a large enough capacity) serving directly to seed the fermentation tanks. [This is the direct pitch method we see a lot of today but grown on premise.]
To obtain a good yeast with pure yeast from the laboratory, it is important to choose the ratio between the amount of yeast and the volume of the must. The yeast must not be drowned in the mass of the liquid, because its multiplication would be too slow. It must, however, have at its disposal a sufficient volume of must. The classical experiments of A. J. Brown have in fact shown that the yeast only multiplies to a limiting number, and that if a number of cells reaching or exceeding this number are introduced into the liquid, there is no more multiplication. The weight of yeast formed can even be, under these conditions, lower than that of the seeded yeast (Pasteur, Duclaux). The harvest, relative to the unit of leaven, decreases as the importance of seeding increases. In industrial practice, the must of the yeast propogation apparatus is generally started with 1 or 2% of pressed yeast or the corresponding amount of liquid yeast, and that of the mother vat with 10 to 12% of the leaven provided by the previous apparatus. [I think what Kervegant is referring to by yeast only multiplying to a limit has to do with scars appearing on each yeast from budding. I wonder if there is any noted differences between budding and fission yeast. The yeast propogation apparatus also doesn’t seem to being with a single slant, but need a certain colony size to start it off.]
The rate of seeding has a significant influence on the duration of the fermentation and on the composition of the eau-de-vie obtained. Arroyo, in Puerto Rico, obtained, for example, the following results, by fermenting a previously sterilized cane molasses must with different initial cellular concentrations (pure yeast):
The increase in cell concentration has increased the speed of fermentation and the alcohol yield, decreased the non-alcohol content of the distillate, whose aroma and flavor, while gaining finesse, become less complex and more attenuated. The shorter the fermentation, the lower the impurity coefficient.
The must of the leavening apparatus and that of the mother-tub must be sterilized. They are cooled, before seeding, to about 30 °C.
Most often the leavens are not renewed from scratch for each tank: they are primed with a fraction of the previous leaven. Depending on the composition and the richness of the must, one pours on the pied de levain 3 to 6 times its volume of liquid. [This was described happening at Jack Daniels in the Alcohol Textbook 6th edition. These yeast are always mutating and adapting and sometimes will need to be refreshed again from scratch.]
The yeast is kept pure for a variable time, following the precautions taken to prevent contamination. When the fermentation becomes lazy, the attenuation less strong, or that one observes under the microscope the presence of foreign ferments in the leaven, one must immediately renew this one with a culture of pure yeasts. In the system of multiplication of leavens by mothers’ tanks, the renewal must generally be done every 10-15 days, whereas with a good leavening apparatus it will be able to wait several months.
Appliances for the levain.
The simplest method for the propagation of leavens is that of the cuve meres. It consists of preparing a mother vat, fed with sterilized must, with a strong levain of pure yeast, and having this vat produce a whole series of footings as long as the yeast remains sufficiently pure. Pairault advocated at the beginning of the century, the following device for small rhummeries.
The mother tank, placed at a level a little higher than that of the fermentation tanks, so that one can feed them by gravity, must have unit capacity equal to 12% of the volume of the must placed into fermentation every day. It is connected to another similar tank of the same capacity, in which the must is sterilized. The latter is provided as the mother-tub of a metal lid, a tube for steam supplied plunging to the bottom and, at its upper part, a coil in which is passed fresh water to hasten the cooling of the liquid once sterilization is complete.
Pure yeast from the laboratory is poured into a glass demijohn containing sterilized must and cooled to about 30° C. After 24 hours, when the leaven is ripe, it is poured into a small wooden vat containing sterilized and cooled must. The small wooden vat, whose capacity is one tenth of that of the mother vat, is equipped with a lid and 2 side handles to be easily transported. Once this second leaven in full activity, after about 24 hours, it is introduced into the mother tank, after having thoroughly mixed the deposit with the liquid by means of a fire-sterilized iron rod. Then opening the communication valve of the tank to be sterilized and the mother tank, have gradually poured the sterilized must on the yeast. In order to facilitate the proliferation of the yeast cells, at the same time, pure air is bubbled through the liquid by means of a tube which is immersed in the bottom of the main tank and whose curved upper part contains a sterilized cotton column. The air is sent using a small hand pump.
The leaven being in full activity in the mother tank (after 24 hours), the must is distributed between the fermentation tanks, at the rate of 1/10 of the capacity of each one, and one fills them little by little with unsterilized ordinary must. However, the mother vat is left with a stock. (About 15% of the volume of the tank), on which is again poured cooled sterilized must contained in the sterilizer, and so on.
This system, a bit primitive, has the advantage of being put into practice at little cost, without appreciable modifications of the existing equipment. It is especially suitable for small rhummeries, too small to pay for a pure yeast apparatus. But, despite all the precautions taken, the starter is infected quickly enough and needs to be renewed every 15 days or so.
The cuves-mère method is well used in the French West Indies, where many distillers receive, at regular intervals, pure yeast from the specialized laboratories of the Metropolis (Jacquemin, Verbièse, Vitalis, etc.).
Distilleries of some importance, however, must employ preferably pure yeast appliances, of which there are many models: Hansen and Kühle, Lindner, Jacquemin, Fernbach, Barbet, Magne, Pfaudler, etc.
The Fernbach apparatus, built by Lepage, Urbain et Cie, is constituted by 2 closed cylindrical tanks, in internally tinned copper, of 10 hl capacity, sterilizable by the steam and carrying a coil in which can be made to pass either steam to bring the must to the boil, or fresh water to cool it. The must is introduced into one of the vats, sterilized by boiling, and then cooled to 30°. Then, by exerting a pressure of pure air, sterilized by passage through a special cotton filter, one passes the liquid in the second tank. The pure yeast is poured into it by means of a special seeding tube, and a stream of sterilized air is bubbled through. When the leaven is in the process of active fermentation, after about 24 hours, 8/10 of the contents of the apparatus are poured as footing in an ordinary fermentation tank, and the remaining portion of starter is fed with sterilized must from the sterilizer. After 8 to 9 hours, a new leaven can be withdrawn, and this continues until the leaven remains pure. [The main feature here the ability to stay sterile, but it will not hit true sustained aerobic respiration and biomass accumulation.]
The Barbet appliance is a closed vertical copper or sheet metal cylinder, made of two distinct parts: the bottom is a reservoir of juice, while the top comprises 4 to 6 trays on which the liquid forms a thin layer of about 2 cm. thick. The must of the lower reservoir is perpetually fed on the upper plate, by means of a tubular emulsifier operating by sterilized air pressure. The apparatus is traversed by a vertical axis carrying metal brushes, to suspend the yeasts deposited on the trays; it is turned from time to time by a hand mechanism. The apparatus also carries an evacuation tube for air and carbonic acid; sight glasses, to allow following the development of the fermentation; a thermometer; a sterilized air inlet, for direct bubbling; a drain valve with tubing for receiving steam or sterilized air; finally a yeast tubing pure yeast. The air sterilizer consists of a cotton filter enclosed in a steam autoclave, so that one can from time to time sterilize the cotton without having any delicate maneuver to perform. [This seems somewhat capable of allowing incrementally fed substrates that can achieve true sustained aerobic respiration and biomass accumulation.]
The apparatus is sterilized by passing steam at 115° C for several minutes, and then 8-10 hl of sterilized and cooled must is added. We introduce, through the seeding tubing that has been flamed beforehand, about 1l. of pure yeast, and it is strongly aerated to activate cell multiplication. When the must is empty, fresh must is added, so as to fill the lower tank, and the emulsifier is restarted. When the leaven is ripe, only 2/3 is removed and the apparatus is filled again with sterilized and cooled must. The yeast, grown under aerobic conditions, develops rapidly, allowing a new leaven to be withdrawn every 5 or 6 hours. This leaven is used to seed the fermentation tanks directly; however, in the very large distilleries, the use of an intermediate leavening tank is maintained. All necessary precautions are taken to prevent contamination, so that the apparatus can continue to produce pure leavens for several months, without renewal of the original yeast.
Seeding of musts
The seeding of musts can be done by three different methods: priming by an isolated tank, cutting a vat, or yeast recovery. The must itself can be completely or partially sterilized, or left as is with the ferments it contains. [SOS this paragraph needs refining. The difference in these processes is eventually described a few pages in the future. I think cutting is blending which implies back slopping.].
Pretreatment of musts.
To obtain absolutely pure fermentations, it is necessary to carry out a complete sterilization of the must and to carry out fermentation in closed vats. This method, applied in particular in distilleries of starchy materials (Amylo process), is hardly used in the rhummerie. The high temperatures necessary to achieve complete sterilization also have various disadvantages. Transformations of the raw material (caramelization of the sugars, etc) can occur during the heating, which thwarts the continuation of good fermentation progress. Certain aromatic elements, which intervene in the bouquet of the eau-de-vie, are eliminated (1). Finally, the pressure steamers required are expensive and delicate to handle.
(1) It is true, as Barbet has suggested, to collect by condensation the volatile principles and to reintegrate them thereafter. [Arroyo’s idea was that these volatile principles should be locked up as salts while the must is being heated.]
On the other hand, partial sterilization of the must followed by fermentation in open vats, is quite frequently applied. Heating at 80° C is generally sufficient, especially in the case of molasses with a certain acidity, to destroy molds and wild yeasts, as well as vegetative forms of bacteria. Spore-forming bacteria, however, may remain, subsequently pass to the vegetative form and intervene in the fermentation, if the duration of the latter is prolonged. There is also a spontaneous seeding of ferments at the contact surface of the must and the air. The activity of the latter remains very limited, except in the case of long-term fermentations.
We have already described in the previous chapter the Barbet device for the sterilization of molasses musts. You can also use the Houdart, Egrot and Grangé automatic sterilizer-recuperator or the Guillaume, Egrot and Grangé refrigerant sterilizer-recuperator.
This last apparatus consists of a long cylinder placed vertically. The lower part is occupied by a heat recovery coil, the middle part is empty and the upper part contains a coil heated by steam. The juice to be sterilized is discharged by a pump into the heat recovery coil, then rises to the upper part, where it is boiled or even at a higher temperature which can be regulated at will. It then goes down to the middle part, where it stays long enough to ensure perfect sterilization. Continuing to descend, the sterilized juice passes into the recovery coil filled with new juice, to which it gives up part of its heat, and leaves at the bottom, to go into a tubular refrigerant. Auxiliary devices automatically adjust the flow and temperature.
Most often in the rhummerie, we just seed the must, without prior sterilization. In this case, intervening during the fermentation are various microorganisms brought by the raw materials (wild yeasts, molds, microbes). This intervention is also very variable depending on the composition of the must. Relatively large in the case of cane juice, it is very small in that of syrups and freshly made molasses. The use of antiseptics also greatly reduces the action of spontaneous ferments.
The addition to the unsterilized must of a vigorous leavened starter is generally enough to ensure the predominance of the pure yeast. But the rigorous control of fermentation and the quality of the product obtained can not be achieved. This method, however, is the only method applied in the distilleries of the French West Indies working with pure yeasts, because of the high fuel costs involved in the sterilization of musts.
Isolated tank priming.
In the isolated tank priming process, a new footing is made for each tank. When the fermentation takes place spontaneously, the clear liquid of the fermented vat is decanted and fresh must is poured on the bottom of the vat, which is formed largely of yeasts. This process is still used by some distilleries, particularly in the production of the grand arôme rums of Martinique. However, it gives frequent miscalculations, and it is generally preferred to completely evacuate the yeast deposit and proceed to a rough cleaning of the tank.
In the case of fermentation by pure yeasts, one sends in the vat a footing of leaven, on which we cast the must. It is then necessary to have a leavening apparatus with continuous production (Barbet, for example) or to have an intermediate mother vat for the propagation of the yeast provided with pure cultures by the apparatus. The installation of the mother tank, which is generally open and fed with sterilized must, has the disadvantage of increasing the risk of yeast contamination. It is however necessary in the big distilleries.
To be sure of the rapid invasion of the must by the yeast and to stifle the development of foreign organisms, it is important to introduce a large quantity of yeast into the must. However, it is necessary to avoid seeding too richly, which is not only expensive, but also hinders the multiplication of the yeast, whose vigor is diminished.
The size of footing relative to the total mass of the must depends on various factors: vigor of the yeast, temperature of the mash, size of the vats, etc. It must be even larger if the yeast is less vigorous. A high must density, high acidity, low temperatures are generally all factors that can slow down the action of yeast resulting in the need to seed at higher doses. In a tropical distillery, a quantity of leaven usually varies between 5 and 8% of the volume of the liquid to be fermented. The dose is sometimes raised to 10%, when we want to obtain rapid fermentations, but in this case we run the risk, especially if we use tanks of large capacity, to have a too rapid rise in temperature. In temperate regions, the proportion of yeast is raised in some cases to 20 and even 25%.
The isolated tank priming method is by far the most used in the rhummerie. It is the only one that is applied to Martinique for example, where the regulations of the Régie, which is based on the attenuation of the musts to control the production, oppose the cutting of the vats. [Regulations somewhat force their production methods. Régie may be their TTB.]
Cutting the vats.
There are several modes to operate by cutting. The most common is to use successively each of the vats as the mother vat, to provide the necessary liquid for seeding the next vat. When the first tank, whose fermentation was initiated with a yeast footing is filled, it is shared with the second vat and fresh must is poured on the two vats. Once these are full, we isolate the first, which we abandon to fermentation until it has fallen, and we cut the second tank on the third. The work is continued thus regularly until the first vat, distilled and empty, is again seeded with the cutting of a previous vat and enters the circuit. To be able to carry out the cutting, the tanks must be connected to each other by means of a communication pipe, located at about half the height of the tanks and joined to each of these by a tap. [This is more a circular technique than working up in volume.]
The volume of the pied de cuve used can vary within fairly wide limits: between 1/2 and 1/4 of that of the tank to be cut, according to the multiplication coefficient of the yeasts footing (L. Lévy). With musts that are not very nutritious, such as beetroot musts, it reaches half the capacity of the vat.
The cutting is done at the end of the period of increase of the yeast; it is better to go beyond this stage somewhat than not to reach it. In practice, the moment is adopted when the abbreviated density (1) is 0.5 to 1° lower than the drop density. In the case of low-concentration musts, we usually choose for the cut, the density difference of 0.5.
(1) The abbreviated density δ is given by the formula: d=1+ δ/100
or d is the number indicated by the legal density. For example, a 1.040 drop will have an abbreviated density of 4°.
The speed of fermentation is accelerated by adding the liquid to ferment in successive fractions, instead of adding it in one single block. Most often, we make the must arrive in infinitesimal fractions: it’s casting. This addition must be driven slowly enough so that the density δ of the tank footing is maintained constant, without getting up again. The filling then requires more time, but once the tank is full, it can be immediately cut off.
A second method is to cut several vats at a time, so that at the end of the operation, the level is the same in all vats. Perard has shown, by calculation, that it is advantageous, in order to reduce the duration of the fermentation, to carry out the cutting of n vats with the (n + 1°) and to operate on the largest possible number of vats. But practically, we do not usually exceed 12 tanks, because beyond the difference in duration becomes very low, while installation expenses increase by one unit each time n itself increases by one unit. The operations will follow one another in time, for any tank, the 6° for example:
— 1st filling by cutting with 3 other tanks, so that the level is the same in all the tanks;
— 1st casting;
— 2nd cutting with the 7th tank;
— 2nd casting;
— 3rd cutting with the 8th tank;
— 3rd casting; etc… until the sixth casting, at the end of which the filled tank will be emptied and left to itself to allow the fermentation to finish in free fall, without cutting or casting.
This process, which increases the speed of fermentation, has the disadvantage of requiring more careful monitoring. It is especially interesting when one wants to force the production of the factory with a given material. There are, moreover, intermediate methods between the two preceding processes: in certain distilleries, the practice of pouring on 3 vats is practiced.
The Guillaume, Egrot and Grangé method carries out continuous fermentation. A large tank, called the principle fermentation, seeded at the beginning of the campaign with a leaven of pure yeasts, is fed continuously with fresh must. It supports fermentation alone and receives absolutely all the sweet juices. A continuous amount of fermented juice is added to this vat, and an amount is sent to a lower tank, of much smaller dimensions, where the fermentation is completed and from which the juice passes to the distillation. The rate of the flow is regulated so that what remains in the principle tank matches the volume of juice necessary to ensure the fermentation at the desired point of the fresh must it receives. To facilitate the installation, the main fermentation tank can be replaced by two twin tanks, and the liquidation of the juice by means of four drop tanks.
In the Alzola system (1), derived from the previous method, the fermentation is carried out in 5 closed vessels of the same capacity, arranged in battery. The first vat, initiated by a leaven of pure yeast, receives all the must; the overflow flows into the 2nd tank of the series, from it into the 3rd and so on until the 5th tank where the fermentation ends. The density decreases progressively from the first to the last tank: from 7° Baumé for example, in the 2nd, it falls to 4° B. in the 3rd, 2.5 B in the 4th and 2° B in the 5th. The carbon dioxide released in the first two vessels is collected and sent into the last two to facilitate agitation of the liquid towards the end of the fermentation. [This is fairly easy to understand and I wonderful how successfully it was implemented.]
(1) in Owen (W.) — Modern distillery design, Sugar XXXVII, No. 3, 26, 1942.
Tournefler installed a continuous fermentation process at the Artenay distillery (France) a few years ago, which requires only minor modifications to the piping of the existing vat room. The Artenay distillery has a vat of 12 tanks of 400 hl capacity and uses the yeast recovery process. Perard described the installation (2) as follows: [yeast recovering is at the core of a lot of modern processes.]
(2) Bull. Ass. Chim. LVI, 235, 1939.
“In the application of the continuous fermentation process, 8 of the tanks communicate with each other, thus forming in a way a single tank of large capacity and the casting of yeast-saturated diffusion liquors takes place on the first 7 tanks. The 8th, which is not flowing, communicates with the 9th through the drain piping; this 9th tank communicates with 10th and 11th alternately by the cutting pipe. This last device was made at the request of the Régie, to allow the compulsory control of the volume of wine produced and sent for distillation. ”
“The must arriving at the end of its circuit is completely fermented, and it is alternately either in the 10th, or in the 11th tank that it encounters a pump which pushes the must through an Alfa-Laval centrifuge, to obtain, on one side, the yeast free wine, which returns to the 12th 12, and on the other the yeast concentrate, which is mixed with the diluted juice for pouring on the first 7 tanks… ” [In modern practice, this yeast mousse is often washed first with sulfuric acid.]
“The gravity of the casting juices is set at about 5.5 to 15°. These juices are cooled to 19-21° C. The density in the head tanks is maintained at 0.3-0.5 and the temperature at 31-33°C; the rise in temperature during the fermentation is also relatively low, it does not exceed 1 °C … Tournfier recommends to conduct the pouring in order to maintain as constant as possible a wine richness equal to 7.7 GL. He remarked that below the value of its cell saturation was increasing rapidly.”
Cutting fermentation methods have very significant advantages over isolated tank priming. The duration of the fermentation being reduced, the capacity of the vat room is significantly smaller, which reduces the expenses of first establishment. The expenditure on yeast is also much less. On the other hand, the purity of the yeast can not be kept intact, unless the normal must is previously sterilized. In the case of green cane juice in particular, rich in microorganisms, natural ferments would happen to predominate rapidly on the cultured yeast. In order to have relatively pure fermentations, it is necessary to liquidate the mother vat from time to time and to restart it with a new leaven. Finally, fermentation by cutting can only be used with light, easily fermenting musts (beet juice). In the case of dense musts and those whose fermentation is difficult (beet molasses), it is necessary to prime each vat with a yeast footing.
In the rhummerie, the musts of vesou and molasses of average density lend themselves well to the use of the method by cutting. This method is however little used: in certain distilleries of Guadeloupe, one applies the process of casting on 2 tanks.
The yeast recovery method consists in recovering by centrifugation the yeasts that are suspended in the fermented liquid and using them for the fermentation of a new tank. The amount of yeast mixed with the casting must be such that it is saturated with yeasts, and the formation of new cells is limited to the greatest extent possible. By taking certain precautions, it is possible to reuse the yeast in a continuous way throughout a campaign. [Keep in mind, yeast are produced at the expense of potential alcohol so this is all about efficiency.]
The factory process of Melle – F. Boinot (1) is applied in the following way. Before being sent to the wine tank of the distilling apparatus, the fermented must is passed through a centrifuge. This gives, on the one hand, an alcoholic liquid almost free of yeasts, which is sent to the column, and on the other hand, a muddy liquid, a sort of concentrated dilution of yeast, which is collected in a specially equipped beaker with an agitator. Yeast milk is supplemented with nutrient salts (ammonia salts, phosphates) and a high dose of sulfuric acid to bring the pH very low (sometimes to 2.5-2.7). After a certain period of contact, the yeast beaker is either sent totally into a tank on which the juice is poured to ferment (fermentation by isolated tank), or mixing gradually with fresh juice (fermentation by cutting). The liquid sugar must have after casting, a slight cellular supersaturation, that is to say a number of cells a little higher than the “limit figure” of Brown, which we realize by counting cells. By adjusting the speed of the centrifugal separator it is easy to leave in the yeast milk only the quantity of cells necessary to obtain this result. [Very clever on changing the centrifuge speed! I always thought it was all or none.]
(1) Int. Sug. J. XLI. 466, 1939.
In the Hildebrandt and Erb (2) process, which is inspired by that of the Melle Factories, the appropriate cell concentration is achieved, so that there is no more yeast multiplication during the fermentation, in a diluted solution of vinasse, and the molasses are then added to the latter so that the richness of the must reaches 15 gr. of sugar per 100 CC.
(2) U.S. Patent 2,169,244, 1939.
Melle’s process can be considered as the most important progress made in the distillery for half a century. Cell reproduction being very limited, the sugar of the must is entirely used for the zymasic yeast function, which allows an appreciable increase in the yield of alcohol. This yield reaches from 100 kgs of sucrose to 61 to 62 liters of alcohol and even, under very favorable conditions, up to 100% of Pasteur’s yield (64 l. 3). According to Boinot, the increase in yield, as compared with the ordinary process, varies from 3 to 30 per cent, according to the nature of the raw material employed, the maximum increase being obtained with those which are difficult to ferment, such as sulphited liquors.
The must being inoculated at once with the normal quantity of yeast cells, the diatase activity is brought to its maximum and the duration of the fermentation greatly diminished. Compared to the ordinary method, the method of Melle would increase the fermentation rate from 40 to 80% (Boinot). As a result, it is possible to reduce the capacity of the vat room. This reduction is made even more sensitive, because it is possible to ferment musts much denser. According to Hildebrandt and Erb, it would be even with musts with a high concentration of sugar (20 gr per 100 gr, must) that yield increases would be the most sensitive.
During the centrifugation of the fermented wine, the bacteria and wild yeasts are eliminated for the most part, because of the density difference between these ferments and the cultured yeast; according to the speed of rotation of the centrifugal separator, the influence of gravity is multiplied by a factor of the order of 20,000 to 100,000, which makes the classification by instantaneous density. It follows that not only the yeast is kept pure, but that it is possible to obtain, from a contaminated tank, a purified yeast concentrate. Practically, vats blocked by infection could be put back into working order in less than 36 hours, without having to use a new leaven, by the only use of yeasts removed from the infected medium (Boinot). [A fascinating idea, but I have a feeling it did not pan out. Possible it worked on bench scale batch centrifuges, but did not scale up to a continuous Westphalia style design.]
An accidental stoppage of work has no effect on the proper functioning of the fermentation. The action of a low pH during the period of inactivity of the yeast, between two successive fermentations, provides it with excellent protection, especially against flocculant bacteria (1). The fermentations that are produced from yeasts stored for 2-3 days and even up to 8 days, are just as active as the others. Only the proportion of cells which stain with methylene blue has slightly increased. The amount of sulfuric acid added to the yeast concentrate is deduced from that used for the acidification of musts, so that the acid consumption is not increased.
(1) In some cases, there is agglutination of yeast, which can be considered as a morbid condition of the cells and is usually due to the action of special bacteria called “flocculation”. [I really don’t know how to interpret this.]
If we add that, by the use of the method of recovery of yeasts, it is possible to operate the return of vinasses on a large scale and reduce the contamination of distillation columns, which are fed only with clear wines, without yeasts, it will be understood that this fermentation process has spread rapidly. In 1939, a few years after it was developed by F. Boinot and the Melle factories, the method was applied in 70 plants, including 278 in France, and 21 in Brazil, processing beet juice and molasses, cane molasses. etc. [This returned vinasses may be different than conventional dunder and there may be very positive environmental impact for recycling it. Disposal of slops is a big deal in Caribbean production. Not enough research is out there to help producers make big capital investments.]
With regard to the particular case of cane molasses, Vergnaud (2) observed in Brazil that, by the use of the method of Melle, it was possible to obtain with musts of 21° Brix, added from 0.5 to 1 % sulfuric acid increases in yield from 7 to 11%. The duration of the fermentation was reduced to 24 hours instead of 48 h. or more, previously. Finally, the fermentations were very pure, which no longer required the sterilization of musts or the use of a pure-culture apparatus.
(2) Brasil Assucareiro VIII, 92, 1936.
The criticisms that have been made against the process, especially by Bettinger (1), are rather theoretical. If this author has recorded some disappointments in an apple distillery, this may be due to an insufficient development of the method with regard to cider musts (wines with 4-5 ° alcohol).
(1) Bull. Ass Chim. LV. 200, 860, 1938.
In summary, “it is permissible to assert, writes Boinot (2), that the process of recovering yeasts is entirely adapted to the industry … It is ensured that the yeasts recovered at the end of fermentation are vigorous and can be reused in a very prolonged manner in successive fermentations. Its hardiness and flexibility ensure a perfect success of the work, by eliminating all danger of infection and allowing voluntary work stoppages for several days, without it being necessary to restart with new leavens”.
(2) Bull. Ass. Chim. LV, 372, 1938.
It remains however that in the rhummerie, the application of the process can lead to changes in the rate and the nature of the impurities that are detrimental to the quality of the eau-de-vie. It does not appear, however, that these fears are well founded, at least in the case of the manufacture of light rums. This fermentation method was indeed applied to the factory Darboussier (Guadeloupe) in 1939, and the quality of the rum obtained proved to be as good as before, when one worked by the ordinary method with pure leavens.
Practicals of fermentation
Pace of fermentation.
Depending on the composition of the must and the production methods applied, the fermentation process is quite variable.
Pairault describes the process as follows, in the case of musts of vesou delivered by spontaneous fermentation and having an initial density of 1.045-1.050, an acidity close to 2 gr. per liter and a sugar content of 11.5-13%.
“The ambient temperature being 25 to 28°, the fermentation is established very quickly of itself, after 12 hours, the tank is in motion. The fermentation lasts generally 3 days, sometimes 4, but often also less … The temperature rises rapidly to 37-38 °, sometimes even up to 40 and 41 °, without the yield suffering in a way appreciable. At the same time, the acidity amounts to 5 and even 6 grams per liter; the sugar disappears entirely. There is little scum, which is also removed in one go after 24 hours of fermentation. The bubbling is intense …”
“When the fermentation is over, the density of the mash has dropped to 1,000, sometimes even a little below (3) (because of the temperature). At this moment, the grappe has lost its sweet taste, it has become bitter, it clears easily. We leave a few hours at rest, withdraw the liquid and send it immediately to the still. Then, remove a wooden pad that closes an opening at the bottom of the tank. The yeast deposit is poured out, washed slightly with a few buckets of water, it is put back in place and the tank is ready for a new charge.” [We see here that they used a false bottom on the tank.]
(3) 0.985 – 0.995, at the observation temperature (28 – 30° C).
Now that higher doses of sulfuric acid and Am sulphate are employed, the duration of the fermentation is generally reduced to 48-72 hours (4). When a levain is used or cutting practiced, the fermentation can be finished after 24 hours. The hourly attenuation currently reaches is stewarded at 0.1. The increase in acidity during fermentation is also much lower than before.
(4) The main factors influencing the duration of the fermentation are the temperature, the acidity and sugar concentration, the method of seeding, the yeast race, the possible use of mineral salts and activators. (carbon, etc.). The initial concentration of the must in the sugar is not very important, if it is maintained between certain limits (10-13 %).
The fermentation of molasses musts is more tumultuous than that of vesou musts. If it is done spontaneously, it lasts in general 6 days, but in the case of high-density musts, including a high proportion of vinasse, the duration can be increased to 10-12 days [Pombe yeast is likely in this latter case.]. When primed by a pied de cuve, the fermentation of ordinary musts is, on the other hand, a term of only 48 to 72 hours, and even 24-36 hours (4), if we operate by cutting. The increase in acidity is very variable: from 4 to 5 gr. originally, it often goes to the end of fermentation at 6-8 gr., in the case of spontaneous fermentation. Exceptionally, for some musts intended for the preparation of full-bodied rums, the initial acidity reaches 12-15 gr. and the final acidity 18-20 gr. (1). In fast fermentations, in the presence of antiseptics, the increase in acidity is low. [Here we see some firm numbers American producers can compare their production to if they employ titratable acidity.]
(1) Even in the manufacture of the German Rum of Jamaica, the final acidities of 30 gr. per liter, of which 15 – 20% are volatile acids.
By properly adjusting the initial acidity of the must (in the vicinity of pH 4.5), it is possible to, when working with pure leavens, to suppress any formation of acids during fermentation. Useful in the industrial alcohol distillery, where one seeks to obtain the maximum alcoholic yield, this way of doing is no longer suitable in the rhummerie, where the acids formed play a useful role in the constitution of the bouquet of the eau-de-vie.
The density drop during the fermentation (attenuation) is variable according to the richness of the must in sugar. In Martinique, where there is a low density load and a high proportion of vinasse is used, it is generally between 32 and 40 degrees regularly. In English Guiana, it is 50° on average and in Jamaica, it sometimes reaches up to 60°. [These appear to be degrees of specific gravity.]
Instead of distilling the must at the end of the alcoholic fermentation, some rhummiers wait a day or two or more (grand arôme rum). The vat is then covered with a dirty gray film of mycoderma and mold. The yield of alcohol is slightly decreased, but a more aromatic and soft product is obtained. Arroyo, advises, even, especially when one wants to obtain Jamaican-style high-flavored rum, to inoculate the must, once the main fermentation is over, with microorganisms likely to attack the residual sugars and to give aromatic products contributing to improve the bouquet of eau-de-vie. Some butyric bacteria may be of interest in this regard.
The amount of heat released by the alcoholic fermentation is high: 20 to 23 calories per 180 gr. of decomposed sugar (Bouffard). In tropical distilleries, the thermometer can rise, during fermentation, up to 40 and even 42 ° C.
High temperatures reduce the activity of yeast, especially in the presence of high alcohol levels, and promote cell autolysis phenomena. They also increase the danger of infection by certain thermophilic microorganisms (lactic bacteria, etc.), especially when the fermentation is carried out spontaneously, as well as the losses of alcohol by evaporation. At the same time as the alcohol yield is reduced. secondary products of fermentation (acrolein, empyreumatic oils, etc.) are formed which depreciate the eau-de-vie. Jankovic (2), for example, observed that in the case of beet molasses musts, the production of empyreumatic oils increased with the rise in temperature and the concentration of the nutrients. On the contrary, it decreased with increasing acidity.
(2) Arch, Hemiju I, 218, 1927.
Arroyo found that the rums produced at relatively low temperatures (27-30° C) were always more mellow, fresher and possessed a more pleasant bouquet than those obtained at high temperatures (35-40° C). Yeasts form more esters and other aromatic principles, when it works in fresh medium.
The above author has obtained the following results in tests carried out with a resistant yeast (No. 1) and a highly susceptible yeast (No. 2) at high temperatures.
High temperatures accelerated fermentation, increased the proportion of higher alcohols formed, decreased alcohol yield and distillate quality. Temperature acted in a much more accentuated way on budding yeast, not very resistant (optimal temperature 28°), than on that with scissiparity [fission] (optimal temperature 32°). The distiller must therefore strive to avoid excessive temperatures and, if possible, stay below 35°C.
The main means of controlling the temperature are: the choice of a suitable location, fresh and ventilated, for the establishment of the fermentation workshop; the use of tanks of moderate capacity; adjusting the sugar concentration; finally the refrigeration of the musts.
When the composition was made using hot vinasse, it is necessary to cool the must before sending it to the vats. For this purpose, tubular refrigerants are used in modern distilleries. These of which there are many models (Venuleth and Ellenberger, Egrot and Grangé, Paucksch, etc) consist essentially of a bundle of tubes, inside which circulate the must, while one passes water cold in the opposite direction, in the intertubular space. When there is a shortage of water, it can be cooled before it has been served by passing on simple air coolers (bâtiments de graduation). [Not sure how exactly to translate that last part.]
The cooling of the tanks is done either by water runoff on the walls (sheet tanks), or more frequently by means of a coil with cold water circulation, that is located at the top of the tank. It must be easily removable for cleaning.
In the tropics, the temperature of the cooling water, is generally around 25-28° C, allowing only a small effect on the fermentation temperature. In order to obtain appreciable cooling, it is necessary to add ice water to the water or to lower the temperature by means of refrigeration, which is an operation that is too expensive to be practical. Also in the rhummerie, it is generally enough to bring the mash to 28-30°, before sending it to the vats, without trying to cool during fermentation. Some twenty years ago, certain industrial distilleries in Martinique had installed serpentines for refrigeration in the tanks. These devices, which have the disadvantage of reducing the capacity of the tanks and require frequent cleaning, have been abandoned everywhere in the colony.
Practically, we avoid too high temperatures by using tanks of moderate capacity (maximum 60,000 liters and very often much less) and reducing the saccharine richness of musts: 8-10% in general, except in the case of slow fermentations, where the sugar level can be raised to 15%. Probably the most practical method is to apply the method by cutting, adjusting the pouring so that the density is maintained constant in the fermentation tank; under these conditions, the rise in temperature is very low.
Materials and the fermentation workshop.
Capacity and number of vats. — The size of the fermentation tanks varies greatly with the country and the working conditions of the factory.
In the early days of the rum industry, wine barrels and syrup barrels were commonly used as fermentation vessels. The use of these, despite their multiple disadvantages, has been maintained in the small rhummeries of the West Indies until the end of the last century.
Wray in 1848, recommends tanks of 1,000 to 1,500 gallons, each having the same capacity as the boiler of the distillatory apparatus (discontinuous stills). These tanks, built in hardwood and 20 in number, should according to the author, preferably be embedded in the soil so as to have a more regular fermentation temperature and less leaks. To guarantee them against the attack of termites, they are coated inside with a good layer of a mixture of “doumier”, tar and oil with a small amount of arsenic. “Those cisterns or tanks are then,” writes Wray, “arranged in lines, separated from each other by an interval of about 2 feet; they must leave free, in the middle of the local reserve for fermentation, a space 6 feet wide along the entire length of this room. The space between the vats, as well as the large empty space of the center, is filled immediately with good dry clay, up to the level of the upper edge of the vats; the clay is strongly packed, to make it firm and solid “.
Fermentation tanks have been maintained in Jamaica, where, however, they tend to be replaced more and more by elevated tanks above the ground. The capacity of the latter is generally low: 3 to 4,000 gallons in general.
In Martinique, the tanks used at the end of the last century also had a low capacity, both in the large industrial distilleries of St-Pierre and in the agricultural rhummeries. “There were some,” wrote Pairault, “of all sizes, from 400 liters to 2,000 and 2,500 liters, a size rarely exceeded. Tanks of 700, 900 and 1,200 liters were the most used.” It was not uncommon to see in the same distillery, and often in the same workshop, vats of different sizes. Some rhummeries of this time having a strong capacity of production (3 to 5,000 liters of rum per day of 12 hours), it was necessary to multiply unduly the vats, whose number sometimes reached up to 400. The space being limited in St-Pierre, one was often obliged to arrange the vats on 2 or 3 superimposed floors, separated only by a slatted floor. It goes without saying that this arrangement was very bad, because it was impossible to wash the floor or tanks of a floor, without the risk of infecting the lower tanks. [Somehow I am attracted to the chaos he is describing.]
Today, much larger vessels are used in the French West Indies. If in the small agricultural distilleries there are still tanks of 2 to 3,000 liters, the capacity of those of the important distilleries generally varies from 20,000 to 60,000 liters. The most used are the vats of 10,000 (agricultural rhummeries), 20,000, 40,000, 50,000 and 60,000 liters (industrial rhummeries). Their number generally varies from 8 to 12. Exceptionally, at the rhummerie du Galion, where they make a grand arôme rum by long-term fermentation, there are 42 tanks of 10,000 liters.
According to Pairault, the capacity of the tanks is, in English Guiana, from 2,500 to 10,000 gallons (5,000 gallons most often); in Dutch Guiana, 18,000 liters; in Haiti, from 200 to 10,000 liters; in Mauritius, 30,000 liters.
Calculation of the vat room. — These are the average tanks that are the most interesting from an economic point of view. The small tanks have the disadvantage of being expensive (because of their large lateral surface), occupy much more space and require a labor abundant for manipulations. In addition, they cool easily, which can thwart fermentation when the ambient temperature, at certain times of the year, is not high enough. On the other hand, in the case of spontaneous seeding, fermentations are, in the tropics, faster and more regular.
Large tanks are also more expensive than medium capacity ones at least when built of wood. They expose one to considerable losses, in case of an accident. They have a tendency to warm up a lot during fermentation. Finally, the fermented must can acidify during distillation and emptying, which are long.
In large distilleries in Europe, tanks of 60,000 to 70,000 liters are considered the best, but in some cases the capacity can be increased to 150,000 liters. In the tropics, tanks of 30,000 to 40,000 liters are preferable because of the tendency to heat up; it is not advisable to exceed the capacity of 60,000 liters. However, in the large Brazilian distilleries, especially in Santa Teresinha, closed iron tanks of 75,000 liters are used, but these must be equipped with a cooling device.
In addition to the amount of must to be processed and the economy of installation and operation, various considerations may be involved in determining the volume of the tanks. It is particularly appropriate when using discontinuous stills, that the capacity of each tank is, depending on the number of distillatory apparatus, so as to treat only properly fermented musts. When fermenting is started with one footing of yeast, it is important that the capacity of the vats is such that loading can be started at the rate of yeast production (every 6 hours, for example). In the case of long-term fermentation, the unit capacity of the vats should be lower and their number higher than in the case of short-term fermentation, so as to ensure the continuous operation of the plant, etc.
The number of vats is linked to their volume by the following formula:
N = 1 + TJ/24V
where N is the number and the volume of the vats, T is the working time of the vat (filling, fermentation, cleaning) and J is the daily amount of mash to be treated.
In the case of insolated tank priming, J / N = 6 is generally taken, when J is very large, and J / N = 4 when J is smaller (Levy). It is also necessary to provide for the preparation of leavens, one or two intermediate vats, whose volume is generally equal to one third of that of large vats.
When cutting is used, the size of the vats is a little arbitrary, because one can work with a number varying from 5 to 12. Perard, based on theoretical considerations, concludes that it is better to have in this case 10 or 12 tanks.
Types of vats — Until the last 20 years, wooden vats were pretty much the only ones used in rhummeries. They have the disadvantage of favoring infections because of their porosity (1), and being difficult to clean, the wood being a poor conductor of heat and penetration of antiseptics being slow. To avoid the absorption of the must by the wood, it has been recommended to brush them with boiling linseed oil or with shellac, rosin and turpentine varnish.
(1) Lamer found wild yeasts and molds up to 5mm in the thickness of the staves.
Sheet metal tanks, which are easy to clean, tend to be used more and more. They have the disadvantage of being attacked by the acids of the must: the iron which enters in solution can in certain cases exert a toxic action on the yeasts (Owen). To overcome this disadvantage, today steel and copper alloys (about 0.20 to 0.25% copper) are used. This last metal tends, according to Weiner, to maintain the oxidized iron on the surface of the steel and to produce consequently a coating very resistant to corrosion. Stainless steel is particularly suitable for the construction of tanks, but its cost is still too high.
In some old distilleries of South America, fermentation vessels made entirely of copper are found. This metal also has the defect of being attacked by the acid of must. However, copper salts, at a dose of more than 28 mg per liter, greatly hinder the reproduction of the yeast and determine languid fermentations.
Stone and cement tanks are sometimes used, but they are not recommended. The stone is rough and full of small cavities that are difficult to clean. The cement has the disadvantage of being porous and giving rise for a long time to alkaline seeps.
The feeding of the vats is still done often, especially in the small distilleries, by square or rectangular wooden gutters. These pipes, that it is almost impossible to disinfect properly, are formally prohibited and replaced by metal pipes, with a preference for copper. These must, to avoid the accumulations of germs, be dismounted easily and not present sharp elbows.
Cleansing of the tanks — The cleaning of the tanks is often very basic and limited to rinsing with a few buckets of water. When working with pure yeast, it is necessary to carry out a more serious disinfection, by brushing them, for example, with a whitewash and ending with a rinse with pure water. If the purity of the fermentations leaves something to be desired, it is preferable to resort to antiseptics: hypochlorite of lime at 5° Baumé, bisulphite of lime extended by 10 times its volume of water, etc. For wood vats, one of the best disinfectants is diluted sulfuric acid. Avoid the use of soda or lime, which alter the fibers of the wood and make it spongy.
The cleaning of the pipes must be done with the greatest care, by keeping the steam for at least 3/4 of an hour, so as to surely reach the temperature of destruction of the microbes.
Fermentation workshop — The room in which the fermentation tanks, or cuverie, are installed must be clear, fairly tall and adequately ventilated. Wire grills should be established at ground level for the removal of carbon dioxide, which due to its density tends to accumulate in the lower parts of the workshop.
It is important to place the vats on masonry blocks, so that they can easily be seen underneath and one can be aware of leaks. A slatted service floor is set at a suitable height.
The floor of the workshop must be waterproof, paved or cemented, with easy drainage for washing water. The walls, usually built of stone or brick, will be covered up to the height of the tanks with a cement coating. They can also be painted with tar or glaze enamel.
It is essential, in order to obtain pure fermentations, that the vat room be kept in a very clean condition.
Recovery of alcohol and carbon dioxide. — In the large distilleries of Europe and the United States, more and more people are using closed vats to recover alcohol vapors and carbon dioxide.
The carbon dioxide produced during the fermentation entrains a relatively large quantity of alcohol, due to the saturation of the gas by the alcohol vapors. In addition, the evaporation in contact with the air, which is especially evident in the fallen tanks, causes a loss whose importance may be equal to the first. The temperature exerts a great influence on the evaporation losses which double, all things being equal, when we go from 30 to 36 ° C.
The most effective method for capturing carbon dioxide is to use sealed tanks, in which fermentation is carried out under a slight pressure (300-500 gr.).
The alcohol contained in the captured gas is recovered by absorption by means of activated charcoal and subsequent distillation with live steam; or by washing with water in a tower filled with Raschig rings, Kestner or other packing, at the top of which is made to arrive raining water. The quantity of alcohol thus recovered would reach, on average, in agricultural beet distilleries in France, 1.4 liters per hectolitre of alcohol produced (Grimaud (1)). In the tropics, where evaporative losses are significantly greater (up to 10% of the alcohol produced), as a result of the high fermentation temperatures, the recovery rate would be much higher.
(1) Divers procédés de récupération de l’alcool perdu en cuverie. C. R. 8° Cong. Int. des Ind. Agr. 1935.
The carbonic gas of the fermentation, whose production reaches approximately 44 kilograms for 46 kg of alcohol formed, represents a very economical raw material for the preparation of liquid CO2 or dry ice. The latter is widely consumed in the United States and could advantageously replace, in tropical countries, ammonia imported for the production of cold.
The installation required for the production of dry ice is essentially as follows: the tanks are arranged in batteries of 3, provided with a common collector, so as to obtain a steady stream of gas. The gases released at the beginning and at the end of the fermentation are sent to the atmosphere, and it is only when the CO2 concentration reaches 99.5% that they are collected. They are first subjected to washing with water, to rid them of alcohol, aldehydes, etc … entrained. Then, in order to eliminate the last traces of organic impurities that could affect the smell or taste of the dry ice, which must be odorless and tasteless, they are passed through a scrubber fed with a potassium bichlorate solution, a second sulfuric acid scrubber, which absorbs moisture, and a column containing dehydrated sodium carbonate. The carbon dioxide thus purified is liquefied by compression at 160-180 kg, then converted into solid blocks of about 55 lbs, by refrigeration and passage to the hydraulic press. The dry ice yield reaches 75-78% of the weight of carbon dioxide released during fermentation, or about 57 kg per hectolitre of pure alcohol (Owen).
It is also possible to capture the carbon dioxide released during the fermentation in open tanks, or by direct suction in the center of the tank, by means of a cylindrical chute terminated by a frustoconical portion descending a little above the upper level of the tank; either by overflow of gas in a circular ring of 30 cm wide and about 4 cm deep, fixed around the tank and in which the gases are sucked by a fan. In this case, the quantity of alcohol recovered is of the order of about 0.8 l per hl, of alcohol produced (Grimaud).
In tropical countries, facilities for the recovery of alcohol and carbon dioxide are rare. However, the Brazilian plants, which manufacture high-grade alcohol or anhydrous alcohol from cane molasses, have high-capacity closed tanks equipped with scrubbers for the recovery of alcohol. The same is true of the major molasses distilleries in the United States, which frequently manufacture dry ice
The accidents that occur in the fermentation of the musts may be due to physicochemical causes (excessive temperatures, presence of certain salts, etc.) or to the invasion of the vats by harmful ferments, whose development is favored by the lack of cleanliness, the poor quality of the raw material, inadequate sulfuric acidification, etc.
Languishing fermentation. — The phenomenon most often observed is the languor or the complete cessation of fermentation before the complete transformation of sugar into alcohol. According to Arroyo, the normal rate of residual sugars in cane molasses would be between 0.5 and 1.5%. A higher proportion indicates incomplete fermentation.
Many causes can intervene to bring about the slowing down of the fermentation. It can be pointed out especially: a starting density that is too strong; excessive rise in temperature; premature depletion of the nutrients necessary for the yeast and too high a proportion of non-sugar towards the end of the fermentation; a decrease in the diastase activity of the yeast resulting from a poorly adjusted pH or the presence of certain toxic substances (copper salts, formic, butyric and citric acids pre-existing in molasses, or produced by the action of foreign ferments, antiseptic doses too high etc …).
In general, cells placed in unfavorable conditions will languish and become degenerated. It is only after determining which are the unfavorable factors, that we will be able to stop any tendency to abnormal fermentation. If this is due to the depletion of the must in nutrients for example, the addition of Am sulphate, and possibly soluble phosphates will determine a new start of the fermentation. When it is necessary to incriminate the presence of copper salts, dissolved during the preparation of leavens in copper appliances or introduced by the vinasse (1), the contaminated must is diluted with fresh must, and so on. The use of finely divided inert materials (charcoal, bagasse, etc.) often gives, apart from any specific treatment, satisfactory results in the case of lazy or incomplete fermentations.
(1) When the distillation apparatus is not carefully cleaned after a stoppage of the distillery, the fermenting must dissolves often appreciable quantities of copper, which are introduced in the manufacture if one practices the return of the vinasses. The first vinasse collected must never be used for the composition of musts.
According to Owen and Calma, the copper would already begin to interfere with the fermentation at the low dose of 0.025 p. 1,000. Cane molasses usually contain small amounts of this element: 0.00091 to 0.00265%. The addition of vegetable carbon reduces the harmful effect of copper (Cent. Bakt. Parasitenk. LXXX, 227, 1930).
Acetic Fermentation — Acetic fermentation, which was so common in the past in rhummeries, has lost much of its importance today as we know how to prevent it. It develops especially in fermented musts low in alcohol, especially those of vesou, and which one leaves to oneself a certain time before distilling them. It is favored by too high or too low fermentation temperatures, which reduce the activity of the alcoholic ferment; poor cleaning of tanks and fermentation equipment; by the use of too low doses of leaven; by a large contact of the must with the air, etc.
Acetified musts give off a strong smell of vinegar. Not only is the yield of alcohol is greatly reduced, but the brandy obtained is of lower quality, as a result of an abnormal content of volatile acids.
To avoid the development of acetic bacteria, it is necessary to observe the utmost cleanliness in the manufacture and to pay particular attention to the perfect state of the vats and the conduits. It is also important to have wines with a suitable alcohol content and to distil the vats as soon as alcoholic fermentation is complete.
Butyric fermentation — Butyric ferments are found only in the musts, where they sometimes play a useful role (especially in the production of grand arôme rums), if they do not take an exaggerated development.
Their development is favored by the richness of the must in nitrogenous organic matters (excessive proportions of vinasse or of sludge) and by the relatively high temperatures (optimum 35° C). Butyric bacteria are usually introduced by molasses that have been preserved for a long time and have become infected during this conservation.
The butyric infection, quite rare in the rhummery, is recognized by the slowing down of gassing, the blackish color of the must and the butyric odor released. It is combated by reducing the proportion of vinasse, aerating the must strongly and increasing the sulfuric acid. The affected vats must be isolated and thoroughly cleaned, before being put back into service with a good leaven.
Lactic Fermentation — Lactic ferments only develop significantly when fermentation temperatures are high and sulfuric acid is low. They are found mainly in skimmings abandoned to spontaneous fermentation. They are usually introduced into the must by the soil adhering to the canes.
Lactic infection is recognized by the slowing down of gas release, the increasing acidity of the must and the presence of lactic ferments under the microscope. It is prevented by cleanliness and control of the fermentation temperature. It is remedied by raising the sulfuric acidity and employing antiseptics.
Viscous Fermentation — Viscous fermentations, caused by Leuconostoc and various lactic acid bacteria, are only found in neutral or alkaline environments (defecation foam). The must contains large gelatinous bodies, or is entirely transformed into a viscous mass, depending on the organisms involved. One fights this infection, by acidifying the must.
Martinique was formerly known for a sort of special viscous fermentation, caused by the use of barrels which contained oil as fermentation vats. The must becomes sticky, thick and takes on a yellowish hue; the alcohol yield is very low. This accident occurred during the 2 or 3 fermentations following the first use of the barrels. [I’m betting the oil here is vegetable oil.]
Putrid fermentation. — Bacteria of putrefaction (Bacillus subtilis, etc.), which give the liquid a strong and nauseating odor, only very rarely determine infections in distillate musts, because they are very sensitive to acids and alcohol. It is easy to protect yourself by proper cleanliness.