How sulphuric acid came to be used in rum production? We finally find a clear explanation. The two short papers below came from the 1896 3rd edition of a very rare text called the Overseer’s Manual, printed in Georgetown, Guyana and only held by a few libraries of the world (that would not share their copies). I seem to have the only free floating copy.
There have been some concerns about racism in the term overseer, and no doubt the word has origins in slavery, but it also seemed to persist in the West Indies with a different connotation than the U.S. Few of the writings at the end of the 19th century display the blatant racism of the beginning of that century. In this text, the overseer simply oversaw the estate and all of its various functions and any grossness was mostly extractive colonialism. There isn’t much space in the text for anything but agronomy and civil engineering. The young managers under the overseers were termed bookkeepers, and that term is very commonly associated with the distillery. I’m certainly no expert, but all these terms seem to fade away in the 20th century as labor unions made progress. Colonialism was rebranded in a new dialect, but it was still the same extractive colonialism.
There are four articles about rum in the book. One is not worth digitizing, the other regarding Jamaica rum at Vale Royal is digitized here. The last two are digitized here.
Someone we are introduced to in the text is Dr. Wilton Turner (1810-1855). He is deceased by the time of writing, but had an amazing career in chemistry and a broader impact on industry I was not aware of. We learn quite a bit about him here. He was actually Jamaican born and inherited 1/8 of the Dunbarton sugar estate. He went on to teach college in Europe as well as dabble in industry, of course working with bat guano…, but then emigrated to Demerara to run a sugar estate and zinc refinery.
If we start to classify rum styles by their fermentation styles, using sulphuric acid or shunning it becomes an important distinction.
Directions for the Manufacture of Rum, by the late Dr. Wilton Turner.
The average offal arising from the manufacture of one hogshead of sugar should not exceed 200 imperial gallons of skimmings and 90 gallons of molasses. The 90 gallons of good molasses from Muscovado sugar will make 600 gallons of wash of SG 1.060, and the skimmings will, according to their density, make 250 to 300 gallons more.
[Something to note here is that Imperial gallons are equivalent to 1.2 U.S. Gallons. That is important to interpreting conversion tables featured elsewhere in the book.]
I shall now give the directions for an estate making 3 hhds. of sugar daily.
The still of such an estate should be capable of working off 2,500 gallons of wash per day.
The liquor-loft should be furnished with six vats, each capable of holding the 2,500 gallons required for the day’s distillation. On larger estates the size, but not the number, of vats, must be increased.
In lieu of the ordinary skimmings’ cistern three coolers, each 12 feet by 8, and 1 foot deep should be provided. These are to be placed outside the buildings at a convenient level for receiving the skimmings, and also for discharging them afterwards, by withdrawing a plug into a gutter leading to the mixing cistern.
These arrangements being made, the distillery is in the best possible condition for successfully carrying out my process. But before going further, I must here remark that the greatest cleanliness in all the gutters, skimmings’ coolers, and vats must be observed. This cleanliness must not however, as heretofore, consist of covering them with temper-lime; on the contrary they must be cleansed with acids, with lemon juice, etc., etc. You have all been long aware that temper-lime was the life of our sugar manufacture, and an acid its destruction, and you have long believed the same to be true for the manufacture of rum. The very reverse, however, is the case in the tropical distillery; lime and alkalies are our enemies, acids our friends and assistants.
[This represents one of the big pivot points in rum production. Many islands, not just Guyana, were very lime happy and possibly fermenting at high pH like Rafael Arroyo advocated for heavy rum in the 1940’s. Understanding that Turner passed in 1855, and the information was slow to disseminate or be adopted, I’d guess that the turning point for lower pH processes consciously appearing in rum production to be the 1860’s. Jamaica slowly follows suit with their own version completely based on organic acids. We know that Percival Greg read this text, but did Patrick Neilson, decades earlier, read Turner’s work?]
On commencing to boil sugar, the skimmings’ gutters, and all vessels connected with the distillery having been cleaned with the common lemons, which can always be obtained on an estate, or with water slightly acidulated with sulphuric acid, add to about half a pail of water 3/4 of an Imperial gallon of that sulphuric acid which is known as the Chamber Acid of Commerce, and throw it into No. 1 skimmings’ cooler, which is then ready to receive the skimmings. The acid when good has a density 1.650.
When about 6 or 7 inches of skimmings have collected in No. 1, place the same quantity of acid in No. 2, and this should be sufficient for that day’s work, where the three hhds. of sugar are made with care.
Each cooler now contains the skimmings, and also the acid necessary for making 1,250 gallons of wash. To this skimmings and acid so much molasses must be added as will make the resulting wash of SG 1.060. To determine this quantity the following process must be adopted:
By an inch rule, gauge the quantity of skimmings in No. 1 cooler. Suppose it 6.5 inches, and suppose we find, on trial with a good Twaddle’s Hydrometer, that the SG of this skimmings be 1.075. Every inch of the cooler corresponds to 50 gallons of skimmings, therefore, the quantity of skimmings is 325 gallons; but the excess of weight of each gallon over water is 75 degrees of density. Hence the total excess of weight of the 325 gallons is found by multiplying that number by 75, and is 24,370 degrees [325 x 75 = 24,375 but for some reason he trades the 5 for a zero]. But we want to make 1,250 gallons of wash of SG 1.060, and therefore possessing 1,250 x 60 or 75,000 degrees; the deficiency obtained by subtracting 24,370 degrees from 75,000 or 50,630 degrees of density must consequently be made up by molasses. Now the density of good molasses may be assumed to be 1.400; each gallon will therefore add an excess of 400 degrees—divide 50,630 by 400 and we obtain 126.5 gallons molasses, as the necessary quantity of molasses to be added to the skimmings in No. 1 cooler to make the 1,250 gallons of wash required. If the molasses be bad, or mixed with water, its density must be determined, and the excess of weight is the divisor instead of 400. To measure the molasses, a square box of 37.25 inches interior measurement and 20 inches deep should be made. Every inch of this box contains 5 gallons of molasses. A full box and 5.25 inches of molasses must, therefore, be added to No. 1 cooler, which must then be well mixed with the acid skimmings. The quantity of molasses required for No. 2 cooler is determined by a similar calculation, and added with the same precaution. The boiling of the wash having ceased, the skimming gutters must be washed down with a little acid water; this may be done the last thing at night, or the first thing next morning, the washings being thrown into No. 1 and No. 2 coolers. The cooler No. 3 and the skimmings gutters are then perfectly clean and ready to receive the skimmings of the following morning.
[When you contemplate the size, that box is quite large and quite heavy! I think “boiling of the wash” implies heating of the acidic washing water.]
The sweets in Nos. 1 and 2 coolers having been exposed to the cooling influence of the night air are, at 6 o’clock next morning, drawn off to the mixing cistern. If the process has been successfully conducted, no fermentation will be observed, and the sweets will be quite limpid. The coolers Nos. 1 and 2 must now be washed perfectly clean with cold water, the washings running into the mixing cistern so that nothing may be lost. No. 1 is thus made ready to receive the afternoon skimmings, and No. 2 is reserved for the following morning.
The sweets in the mixing cistern are to be pumped into No. 1 vat without the addition of water. As soon as the pump sucks, allow a few inches of cold water to collect in the mixing cistern, and then without stopping the stream of water let the pump be worked. In this manner the whole of sweets are got into No. 1 vat, and the mixing cistern and pump left quite clean. No. 1 vat must not be filled up with water until the following morning, when only the coldest water must be used. By that time a good fermentation will have been established, which will run its course in 4 or 5 days; the wash should be distilled as soon as the escape of gas ceases, although it will then be still quite hot.
[Turner appears to be describing spontaneous fermentation and that it sets in at a much higher gravity than 1.060.]
Two conditions are particularly necessary to success. The first is that each day’s skimmings be kept by itself, for if the fresh skimmings be contaminated by ever so small a quantity of that of the previous day, fermentation will set in too soon, and occasion loss. The second is that nothing but the best and perfectly fresh temper-lime be used in clarifying the cane-juice. Unslacked lumps of lime, or good lime fallen into a powder from exposure to the air, which contains a large quantity of carbonate of lime, will neutralize the sulfuric acid, and of course, destroy its effects. Where this is observed to occur, more acid must be used, but this is wasteful and the result not satisfactory. Many persons trying my process have failed in obtaining satisfactory results by not being aware of this circumstance.
[Perfectly slaked lime is a free-base and when it goes into the cane-juice it will quickly join with an acid. If the lime is not free and instead bound to CO2, it may not encounter enough, time, heat energy, or a strong enough acid to dislodge the CO2 and find another acid. This excess, sort of unemployed, carbonate of lime would react quickly with sulphuric acid because its such a strong acid and that would be wasteful. It would also damage the aroma, because you would be stuck with too much lime whereas sulphuric acid (and other acids produced in the ferment) will trade places with an organic cane acid so that they may be free to form an ester. However, Arroyo advocated 1 g/L of lime as carbonate to form a sort of time release of maintaining a higher pH as the fermentation produces acids. This was done in high pH ferments that featured no sulphuric acid.]
In making molasses setts, the following plan should be adopted; As 15 gallons of good molasses will make 100 gallons of wash, of SG 1.060, the 2,500 gallons vat will require 375 gallons of molasses. Put this molasses mixed with about an equal quantity of cold water, and 1.5 gallons acid into the mixing cistern, and pump them into the vat, which must not be filled up with water until the following day. As in working molasses alone a deficiency of yeast may occur, it may be well not to wash out the vat, into which the molasses sett is put; but when this is done, the mixture of equal parts of molasses and water with the acid must remain either in the cooling vessels, or the mixing cistern during the first 24 hours, and then be pumped on the yeast in the vat, otherwise the fermentation sets in too soon.
[Notice no skimmings are present, but spontaneous fermentation is practiced.]
The arrangements mentioned above, although of advantage, are not absolutely essential to the successful use of acid. In general, little or no change is required in the existing arrangements of the sugar works, unless the skimmings receivers formerly in use are of mason work, or made of a metal (iron or copper) easily acted upon by acid.
Remarks on the use of Sulphuric Acid as an aid to Fermentation.
[The following is taken from a pamphlet published for private circulation in British Guiana nearly thirty years ago. Some of the most experienced planters in the colony say that notwithstanding the many improvements that have been made in the management of distilleries since the pamphlet was written, its instructions are still of great practical utility.]
[Above are the author’s bracketed comments and not mine. If the comment of 30 years ago is current to the publishing date of 1896, that would mean sulphuric acid use was being taught in the 1860’s well after Turner’s passing. I’m not aware of that pamphlet having a title or being cited anywhere. Could DDL have a copy in their archives?]
The system of preparing wash for fermentation, introduced by Dr. Turner, has now undergone a trial of nearly seven years. During that time difficulties have had to be surmounted, and deeply rooted prejudices overcome, but the use of Acid has steadily gained ground, and has been adopted on many of the largest properties in this colony. If evidence be required to show the value which the gentlemen conducting these estates place upon this process, it is to be found not only in their having in almost every case, after a preliminary trial of considerable duration, purchased the right of using the patent, but in their having continued from year to year to import with great risk, or to obtain in the colony at a high price, the agent which the patentee pointed out as required. In addition to this, in itself very conclusive evidence, the kindness and liberality of some of these gentlemen now enables me to append their written opinions as to what are its chief advantages. These statements are of so clear a nature as to render any comment upon them altogether superfluous; I have merely, therefore, to draw attention to the decided preference expressed by their authors for this as compared with the old method of conducting fermentation, irrespective of any gain in the quantity of spirit obtained, and to the fact that, although showing the latter to be in distilleries previously conducted with care and attention, under what was claimed for his process by the late Dr. Turner, who probably took for his data the results of fermentation where little care or attention had previously been given to the matter, the increase is still amply sufficient to render a careful trial of the process well worth the attention of all who are desirous of increasing the amount of their rum crops, a gain of even so little as five per cent. upon which would much more than repay the cost of the sulphuric acid used,* whilst the cleanliness and rapidity of the fermentation, the small number of vats to be kept in order, and the savings of time and labour, stated by Mr. Kelly to amount to fifty per cent., are alone advantages more than enough to recommend its adoption.
*A gallon of acid of specific gravity 1.600 will, in ordinary cases, be more than sufficient for 1000 gallons of wash, set up at 1.060 (12° Swaddle, or 8° Baumé). This, at three cents per pound (the price at which it can now be obtained in Demerara), costs 48 cents. Supposing the usual return of strong rum to be 70 gallons from 1000 gallons of wash, a gain of five per cent. upon that quantity is equal to 3.5 gallons, which, at the present value of rum in the colony, is worth fully $2.50 No manufacturer in Europe would consider such a gain to be unworthy of his attention; and the accompanying certificates will show that the increase has been usually much larger.
[Something to note so far is that someone is representing Turner’s patent after his death. The same did not happen to Rafael Arroyo who also died untimely. Arroyo’s widow was particularly uninterested in supporting his body of work and may have moved back to Cuba (before I think returning to PR later). No student or associate may been available to support Arroyo’s patent or they may have been prevented because of lack of cooperation by the family. At the moment, I don’t know enough, but patents have long been important to rum production.]
It has been erroneously supposed by many persons, that the application of sulphuric acid as an aid to alcoholic fermentation was, when patented in Demerara, altogether an innovation and novelty in the distiller’s art. In the colonial distillery it may have been, and, so far as I am aware, was so: but in Europe, the cause of loss when fermentation is carried on at a temperature such as that of the West Indies, had been long before investigated by skilful chemists, and the remedy pointed out by them. The addition of a small quantity of sulphuric acid to the saccharine solution to be fermented, had for years previously been in use, even in temperate climates, such as that of France, when molasses whether colonial or the refuse of the beet-root sugar works, was the substance to be treated.
These facts following quotations, from the works of men whose names alone may guarantee the correctness of their statements, will be sufficient to show.
Dr. Gregory, professor of chemistry in the University of Edinburgh, writes as follows:—
“When certain saccharine juices such as those of the beet-root, carrots, onions, etc.” (to which, had it ever come under Dr. Gregory’s observation, he might, with great propriety, have added the sugar cane) “are exposed to a temperature of from 86° to 104°, a peculiar fermentation takes place. The sugar disappears; but instead of alcohol and carbonic acid there are obtained mannite, lactic acid, and a mucilaginous substance having the composition of gum; this latter renders the liquid ropy and viscid, hence the name given to the process.” The liquid soon becomes acid, from the conversion of sugar into lactic acid; but when the amount of free acid reaches a certain point, the fermentation (the viscous) is thereby checked. If, now, the free acid be neutralized by the addition of carbonate of soda, or carbonate of lime (chalk, or unburnt lime), lactate of soda, or of lime is formed, carbonic acid is disengaged, and the fermentation recommences.”
The name of Liebig is familiar to every one as a standard authority on all matters relating to the economy of chemistry. In his familiar letters the following will be found:—
“The influence of temperature on the nature of the products of fermentation is truly remarkable. The juice of carrots, beet-root and onions, which is rich in sugar when allowed to ferment at ordinary temperatures, yields the same product as grape juice; but at a higher temperature the whole decomposition is changed; there is observed a much less copious evolution of gas, and no alcohol is formed.”
MM Pelouze and Fremy, the former professor of chemistry to “the College of France,” the latter occupying the same distinguished position in the “Ecole Polytechnique,” in a joint work, write: “When a solution of sugar is placed in contact with ferment which has been previously boiled, the former is transformed into a mucilaginous matter.”
In describing the method of fermenting molasses practiced in France, the same writers state:—”In fermenting molasses for the preparation of alcohol, it is mixed with ten times its weight of water, and acidulated with sulphuric acid.”
Dumas, in treating of the same subject, makes use of nearly the same words:—”We commence by saturating the molasses with sulphuric acid, after dilution with ten times its weight of water.” And further on in the same work, muriatic, sulphuric, and sulphurous acids prevent viscous fermentation by precipitating the matter which gives rise to it.”
From another and more recent work, now considered as an authority on chemical manufactures, the following is extracted:—”The mineral acids and astringent substances, and especially sulphuric and sulphurous acids and tannin, precipitate the viscous ferment, and are hence the best cure for this malady in fermented liquor.”
To these authorities many others of equal weight might be added, were it necessary. The reader can hardly fail to observe how exactly the conditions pointed out as the most favourable for bringing about that peculiar fermentation which it is the interest of the colonial distiller to prevent (the viscous), are those with which he has always to deal.
The cane juice, originally slightly acid, has, for the purpose of sugar making, been carefully neutralized; a considerable quantity of carbonate of lime (lime sufficiently burnt, or afterwards exposed to the air) always finds it way into the skimmings receiever, and remains there ready to lend its aid to set up and continue mucilaginous fermentation. All the ferment used has been boiled; and the temperature of the vat of fermenting wash, commencing, if the ingredients have been well cooled, at or over 80°, soon rises to a greater heat, often reaching to above 100°. Thus, were the object of the manufacture to produce mucilage, with its attendant products, instead of rum, it would only be necessary to go one step further, and by the addition of lime, or any other alkali, to neutralize from time to time the acid as it is naturally formed in the wash, at the expense of the sugar it contains, by which means the formation of alcohol would be altogether prevented.
The distiller is usually too well acquainted with the appearance of mucilaginous fermentation to render any description of it necessary. It commences in the skimmings cistern, the contents of which, from the gradual accumulation of heated liquid, are kept always at a high temperature, which together with the presence of lime, tends greatly to promote this species of decomposition. Thence transferred to the fermenting vats, it infects the whole wash with the same malady; and this continues till the amount of acid formed is sufficient to check its progress. As acid and alcohol are formed, the mucilage, if in the great quantity, is in party thrown down, and is frequently to be found in the bottoms of the vats, in a form strongly resembling boiled rice, when the fermentation is completed.
The sulphuric acid, according to Dr. Turner’s system, is put into the receiver before any of the skimmings is run into it, and appears to act a three fold part. It destroys that peculiar principle which engenders the mucilaginous or ropy state of fermentation, more particularly active when the ferment has been boiled. It combines with any lime that may be present, reducing it to the state of a harmless sulphate; and, if used in sufficient quantity, it alters the cane sugar into grape or uncrystallized sugar, a change which it must undergo before it can ferment, thus greatly facilitating that process.
If, even in a temperate climate, such as that of France, the use of sulphuric acid has been found necessary to obtain full results from saccharine matter subjected to fermentation, and of this there can be no doubt, for, in addition to the authorities already given, a report on the subject of the production of spirit from the juice of the beet-root, published in Paris, in 1855, states the use of that acid to be a part of the system employed, and gives in a note the reason for its employment to be the prevention of viscous fermentation; how much more advantageous, then, must its use be in a tropical climate, where all the attendant circumstances lead directly to establish that very species of fermentation which the European distiller so carefully guards against. Distillation from beet-root has more recently been introduced into England. The readers of The Times may have observed, in a late article on the subject, that the use of sulphuric acid also forms a part of the process employed there.
Although convinced that the introduction of Dr. Turner’s process will always be found of advantage, still the gain in quantity of spirit obtained must necessarily vary on different estates. The liability to the viscous or ropy species of fermentation is not alike on all estates, nor even on the same estate at all seasons of the year. The quantity of lime used to clarify the cane juice, and the care with which it is prepared and applied, exercise a decided influence on the fermentation of the skimmings and molasses. The excess of lime which it is sometimes necessary to use in order to introduce granulation of the sugar, will, as certainly as it produces the desired effect in sugar making, prove injurious to fermentation. The rapidity with which the offal of the sugar works can be used up after it is made, the purity of the water used in setting up the wash, and the proper ventilation of the fermenting loft, all, more or less, affect the production of spirit. It is on estates where the return of rum has previously been least favourable that the greatest improvement may be expected from the use of sulphuric acid.
In one case, in which I had an opportunity of comparing the working of the two systems over a period of several months, the increase was, as compared with the same period of the previous year, from an average of 95 gallons of strong spirit obtained from each distillation, which was rather about the average when taken over a still longer period, to an average of 123 gallons of spirit of the same strength, or as nearly as possible a gain of 30 per cent., although no change was made excepting the use of sulphuric acid in setting up the wash. On another estate, where I made a very careful comparative trial, during which ever precaution was used to insure as perfect quality as possible in all other respects, the additional quantity of rum obtained amounted to 19 per cent.; whilst the results of a series of most exact experiments made on a large scale by Dr. Turner and myself, during which the whole subject of fermentation underwent a more careful investigation than it had probably ever received in a tropical climate, the increase reached as has as an average of 44.9 per cent.
In the mind of anyone whole will take the trouble fully and impartially to examine into the subject, there cannot remain a doubt that the presence of a certain amount of acidity in wash is absolutely essential to the production of spirit in a climate such as that of British Guiana, and that if the required acid is not only the loss of saccharine matter which produces it, but of a much larger quantity of the same material, which, properly treated, would be converted into spirit, but under the ordinary treatment goes to form the altogether useless substances,—mannite and mucilage. The simple question then remains, whether it is cheaper to lose the quantity of material that is necessarily lost in supplying the required degree of acidity to the wash, or to prevent this loss by the addition of a more powerful and expensive substitute, the advantage of using which has been for many years recognized in Europe, both by men of science, and by practical distillers.