Advanced Hogo Basics with Victorian Rum Genius No. 2

JAMAICA BULLETIN OF THE BOTANICAL DEPARTMENT.
New Series. MARCH, 1895.

RUM ANALYSIS.
By Percival H. Greg.

I do not think I am wrong in saying, that the smell of rum, really good rum that is, is one of the most delicious scents that can be imagined. There is in addition something so peculiar and undefinable about it; it is so different from the smell of any other spirit that the more we smell it, the more we are puzzled to say to what its aroma is really due.

Rum like almost every product of commercial importance has been analysed. The most important work in this direction has been done by foreigners, and those chiefly Germans, who have lately been making a great effort, and will probably continue doing so, to produce a spirit from Beetroot juice, molasses, or cane sugar, to vie with Jamaica rum. So far I am glad to note, these efforts have been unsuccessful, but Jamaica should remember the painful lesson taught by the rise and growth of the Beet-sugar industry, and should take a leaf out of their adversary’s book, in not disdaining to study science in connection with their manufactures.

Up to now analysis of rum, and this remark applies with equal force to brandy and arrack, has been rather barren of results. One of the first aims of analysis of any commercial product, has always been to determine what are the normal constituents of the article in a state of purity, and in what proportions these constituents are present. Unfortunately the difficulties in the way of this are manifold. No chemical analysis so far can tell us, whether a rum has been adulterated or not. In this respect an opinion emanating from an experienced rum dealer, is worth far more than that of the analyst. This however is not so surprising as might at first sight appear. Rum is not a definite chemical product, we cannot write the formula of rum, and any one of its constituents may vary in the proportion in which it is present, or indeed some may be absent altogether, without our being able to say, that such a change is due to artificial manipulation. The great obstacles in the way of analysis of rum, brandy, and arrack, are the large quantities required for analysis, and the consequent costliness of the operation; the uncertainty as to whether the spirit, when this is forthcoming in sufficient quantity, has not been adulterated either at the place of its production, or in its subsequent passage through, other hands; the fact that all spirits undergo chemical changes during storage; and the fact that the particular substances constituting the aroma are present is such infinitesimally small quantities.

These values are in grammes per 100 cc. In order to obtain the weight of ethers present in a gallon of rum, it is only necessary to multiply the fraction of a gramme given by 10×4.5. [for those not yet metric!]

Most writers have attributed the aroma of rum to the presence of Butyric ether, indeed Gaber in his book “Die Liqueur Fabrikation” (Liqueur Manufacture) states that it is only necessary to allow cane sugar molasses to ferment in Europe at a temperature of 40° C. a temperature favourable to the production of butyric acid, and therefore a necessary preliminary condition to the formation of butyric ether, in order to produce a spirit, which after sufficient storage cannot be distinguished from a true rum. But if we glance at the tables we notice that acetic ether is present in far greater quantity than butyric ether, in one case the proportion or acetic ether to butyric is over 200 : 1, and we must therefore conclude that it is to the comparatively large amount of the first named ether, that rum owes its characteristic aroma, in as far as the characteristic aroma is derivable from the presence of ethers. Now in considering these figures from a practical and commercial point of view, we should like to know, what is the influence of the presence of these ethers on the commercial value of the rum : that is, is an increment of ethers present in the sample followed by a corresponding increment in the market price, and vice-versa? On this point the figures given in the preceding table can give us no information, as the money values of the rums are not stated; but in Windisch’s “Brandy Analysis,” I came across some analysis of rum which possess a greater significance for us, inasmuch as the prices of the rums are also given. In following out this idea I selected from a considerable number of examples four expensive and four cheap rums, and then set myself to compare them together with special regard to the quantities of acids and ethers present. In the original work the prices are expressed in German coinage and for the measure of one litre, but in order to make the figures more intelligible to my readers, I have translated them into the corresponding values in English money per gallon.

[Part One of Table / Part Two]

On examining these tables we learn that the expensive rums as a class are richer than the cheap rums in the total amounts of acetic and capric acids, and poorer in formic and butyric acids while the table of ethers shews us that the expensive rums as a class are richer in the total amounts of all the four fruit ethers. It would be very rash however to jump to the conclusion, that the richer a rum was in fruit ethers the higher would be the price which it would command ; a glance at the total amount of fruit ethers present in each of the expensive rums will show that the rum at nine shillings and eleven pence, is poorer in the total quality of fruit ethers than two of the rums at nine and two pence and eight and seven pence respectively. But on the other hand we may observe in the case of cheap rums, that the rum at four shillings is richer in the total quantity of ethers, than the rums at three and two pence, and two and eight pence. In order to explain this apparent contradiction we must remember that the fruit ethers though contributing a great deal, do not contribute everything to the aroma, and also that even if they did, that it is quite possible to have too much of a good thing. It has been found for instance, that by the mere addition of fruity ethers to a neutral spirit, it is not possible to imitate exactly the aroma of a genuine rum. If this were so, in all probability, Jamaica rum manufactured in Jamaica, would belong to the glories of the past! A spirit so treated will have a too pronounced and penetrating odour and a sharp burning taste. “The flavour of a true rum on the contrary is always soft and mild, the aroma appears to be to some extent ‘covered,’ and leaves a kind of oily impression upon the tongue” (Windisch). As regards the other aromatic constituents of rum there remains, the higher alcohols generally grouped together under the name of fusel oil, the organic bases, the essential oil of rum, and a fatty acid of a fruity nature. Fusel oil has generally been identified with amyl alcohol (Iso-butyl carbinol), which possesses poisonous properties, and is of a disagreeable smell, but since higher alcohols do not necessarily mean amyl alcohols, it would be unwise in the present state of our knowledge concerning the higher alcohols of rum to draw any inference as to their influence on the aroma. For the present we merely give the results arrived at in the determination of the higher alcohols, without comment.

This as a general rule in Jamaica consists in treating the cane juice with caustic lime. I determined therefore to try the experiment of fermenting cane juice which had undergone this treatment. But as an alkaline medium is unfavourable to alcoholic fermentation, and as the alkaline skimmings from the boiling house are brought down, whenever possible, on acid dunder, I determined in order to test the efficacy of the treatment and at the same time to provide a favourable fermenting medium for the yeast, to neutralise the alkalinity of the treated cane juice with sulphuric acid, using a sufficient excess to produce a slight acidity : dunder of course could not be used in this experiment. A portion of fresh cane juice was therefore taken and divided into three parts I, II and III. No. I was made alkaline with caustic lime, No. II was not treated and served merely as control experiment, while No. Ill was not treated with temper lime, but was faintly acidulated with sulphuric acid. This last also served as a control experiment, as it might be argued, that should any aroma be produced in No. I sample, it might have been caused, not by the treatment with an alkali, but to the subsequent liberation of aromatic vegetable acids, or volatile vegetable acids, capable of forming fruit ethers perhaps by the stronger acid sulphuric. I must add that in order to preclude the possibility of action of germs other than No. 18 yeast, which would of course be naturally present in the cane juice, that the three portions of liquid were sterilised before being fermented. No. I. was sterilised (boiled) after the treatment with lime, in order to imitate the treatment to which the skimmings are subjected in the boiling house, and the sulphuric acid added just before the fermentation. No. III. was boiled before the treatment with sulphuric acid in order that if volatile acid should be liberated that they should not be driven off by the heating, that is that the maximum effect if any, due to their presence, should be obtained. No. II. sample was of course simply boiled without any addition. After these three samples had been boiled and allowed to stand in contact with sterilised air for a sufficient length of time, an equal quantity of No. 18 yeast, in a state of absolute purity was added to each portion and the liquid allowed to ferment, the outside temperature being the same in each case. In No. I. sample, which had undergone the treatment with lime, the characteristic aroma was developed. In samples II. and III. the aroma was not developed. It is but fair to state that the aroma produced was not very strong, but there was no denying its presence. Here then we have the four factors necessary for the production of the aroma in question. First the germ, No. 18 yeast; secondly, the medium skimmings or cane juice; thirdly, the treatment of the liquid —heating with caustic lime, or caustic alkali; fourthly,the question of time—the wash must stand 24 to 36 hours after fermentation has been completed. Be it borne in mind that the absence of any one of these 4 factors, will result in the non-production of the aroma in question. I expressly state here of the “aroma in question” because it is not contended that no other aroma can be produced by any other germ or germs which may be active in the fermentations. Indeed the treatment with lime for reasons which I shall show at another time, has an effect upon the flavour of the resulting spirit, independent of the action of any particular germ. In order however to make quite sure that the activity of 18 yeast is necessary in treated cane juice to ensure the production of the aroma, treated cane juice was fermented by several other Jamaica yeasts, but no aroma was produced. My researches hitherto have been directed to show that a certain aroma can be produced by a particular type or variety of yeast, which cannot be produced by other germs in my possession, but that though the activity of this yeast is essential, certain other conditions are equally essential. In other words the aroma produced during fermentation is the resultant of more than one force, but that the type of yeast employed plays a very important part in the matter and the probability is that this remark applies to any other aroma produced during fermentation. I have in this case been able to isolate and identify these forces, which is advantageous as showing how No. 18 yeast may be employed to produce the aroma, with its maximum effect. But it will be seen that so far I have touched on the matter somewhat superficially. I have yet to show what is the substance or substances which are acted upon by the caustic lime in the cane juice and the way in which No. 18 yeast acts upon them to produce an aroma, and I have yet to show why the effect of the lime is not rendered nugatory by the after addition of sulphuric acid. This however would make my paper too long and as I am still engaged in investigations on these points, I must defer any explanation for the present. One thing however further experiments have taught me with absolute certainty, that in order that the treatment with lime be efficacious in its influence on the flavour of the rum—and this applies equally, whether 18 yeast is used or not—the skimmings must be thoroughly heated in the syphons after the treatment, with lime.

 

The considerations which led to this discovery were :—
1. The use of alkali in enabling No. 18 yeast to produce its characteristic aroma.

2. The failure to extract any aromatic oils from untreated cane juice, or from rum made entirely from such cane juice.

3. The discovery of this essential oil in Rum made in the ordinary manner.

4. That the treatment of the juice with lime, is the only strictly chemical treatment, to which the juice on the majority of estates in this country is subjected.

The odour of this essential oil may be best described by calling it the essential oil of Rum, since it has a peculiar and indescribable smell of rum, and, without doubt, it is to the presence in it of this oil, that rum owes its characteristic aroma; an aroma which is so utterly different to that of any other spirit. It is of an oily nature, and a small quantity will remain for a considerable time in a glass exposed to the air without entirely losing its strength; and I should say therefore that it is to this property that rum owes its oiliness, “body” and permanency of aroma which distinguishes genuine rum from any artificial imitation. After having been set free by caustic alkali from its combination in a natural state, it does not appear to be further acted upon by alkalis or dilute H2SO4 ; but strong H2SO4 seems to dissolve it with formation of a faint pink colour, which may be due to carbonization. It is readily soluble in chloroform, alcohol, and water. If a portion of cane juice, containing this oil, be filtered absolutely brilliant, the quantity of oil which can be extracted does not appear to have been lessened by filtration. Of course, this does not dispose of the objection that it might be found floating at the top, or forming a layer at the bottom of the liquid, in the form of an oil insoluble and lighter or heavier than the liquid with which it was associated; but, on carefully scrutinizing the filtrate, I have not been able to observe any such phenomenon. It is true that if we take a sample of cane juice, heat it with lime, and then let it settle and absorb air in some deep and narrow vessel, a Nessler’s reagent glass or test-tube for instance, that a band of darker colour may be observed at the top on cooling, but this is due to oxidation, probably of glucose compounds, and, on shaking the tube, the dark brown band at the top mixes easily with the lower portion of the liquid. It is also true that a waxy film may be observed floating on the top of such liquor, but it possesses merely a wax-like aroma, and is probably palmitic acid. That there is a large amount of wax in cane juice has been known for a long lime, and palmitic acid has been found in rum. (Mulder. Jahresbericht für Chemie, 1858, p. 302.) It would appear, therefore, that in the process of manufacture a considerable portion of this aromatic oil will be lost, since being soluble in water it cannot be separated by the preliminary clarification process in the cyphons, but must pass from thence into the coppers, where a good deal of it will be dissipated in the form of vapour. To a certain extent no doubt as the liquor gets concentrated by ebullition, and the essential oil has less water for its solution, and as the density of the liquor increases, it may rise to the top in an insoluble form, in which it can be skimmed off. But on these points further investigation is necessary.

Its boiling point appears to be comparatively high. It comes over from the still in the later runnings and can be extracted from dunder in considerable quantity, and I have succeeded in extracting in small quantity from molasses. The fact of its boiling point being high and that it can be extracted from dunder, shows us at once that we do not obtain by our distillation process, so much of this oil in our rum as we might do. It seems also to indicate that the use of patent continuous stills with high rectifying columns, would certainly be attended with a minimisation of the aroma of the rum in so far as this was due to the essential oil; and it suggests to us as to whether or not this may not be the reason as to why a low still head produces a better rum than a very high one——this seeming to be a pretty general opinion among Planters. If this should prove to be the case, it would seem as if the addition of an extra retort filled with cane juice, which had been properly treated for the production of the essential oil, through which the alcoholic vapours would have to pass, would be a distinct advantage : though certainly care would have to be taken that the lime was not present in excess, as this would lead to a decomposing of the “fruit ethers” which might come over with the alcoholic vapours. It is interesting to note that something of this sort appears to be done in some parts of the colony though instead of lime, common salt appears to be used.

What was said in a previous paper concerning the possibility of the existence of different “fruity acids” in different canes and in different soils, applies equally to this oil of rum. But here again a chemical examination of juice from different sources alone can decide. I am inclined to think however, after having examined rums from different estates and from different parishes, that, with the exception perhaps of the “new leather” smell, which may be caused by the presence in the rum of some single substance possessing that aroma, and which is not found in other rums, that variation is more to be sought for in the quantity in which this oil is present than that different soils each possess a characteristically different essential oil. Turning to the results obtained in the examination of samples of juice taken at different times from the mill from the same estate, I have been surprised by the marked differences exhibited in the quantity of this oil present. In very many cases it does not appear to be present at all. So far the samples have been taken at random from the mill without any attention having been paid as to the soil – on which the canes yielding such juice were grown, or as to the nature of the cane whether plant or rattoon. But having once established these two important facts, viz., the necessity of heating with temper lime or fixed caustic alkali to set this essential oil free, and that the amount in which it is present varies so widely, we are now in a position to carry on a systematic examination of cane juice from different soils with a view to ascertain what is the determining cause of such variations ; while it is evident that until such variations had been proved to occur, that any investigation in this direction could not be undertaken. It may be a matter of surprise to some, that if such variations do occur, that a greater variation in the quality of the rum from the same estate is not noticed. But the truth is that from the nature of our manufacturing process such changes in the character of the juice and the rum manufactured from it, must to a great extent remain hidden from us. In the parish of Westmoreland at any rate, it is the custom to mix and grind the canes from different fields simultaneously, so that the liquor, which finds its way to the still-house, is in no sense a representative sample of any particular cane piece, and the same may be said of the molasses. Coming to the still house, we not only use the liquor of a previous setting, i.e., the dunder, but many estates preserve their dunder from crop to crop; and in so far as concerns the distillation, not only is a double still frequently used, but also a retort containing a charge from the previous distillation, while, finally, the liquor is stored in butts of large capacity before racking into the puncheons. Yet, in spite of all this, anyone who watches the rum carefully, cannot fail to notice variations, and it is notorious that a difference in the quality of the shipments, from the same estate, is often commented on in England.

THE ORGANIC BASES.

But the treatment of the juice with lime also finds expresssion in the aroma and taste of the rum, in a distinctly unfavourable manner. It is owing to this that the organic bases or bodies of an alkaloidal nature are set free and are found in that state in the rum. A sample of rum shaken up with chloroform left behind, in addition to the essential oil, a vile smelling residue, the smell of which completely hid that of the essential oil, and resembled almost exactly the smell and taste of the dark brown liquid which may be found in the stem of a foul tobacco pipe. There seems very little doubt that this must be due to the presence in the rum of some organic base of the pyridene group, and last crop I succeeded in producing the same smell in cane juice by heating it with excess of caustic lime. During this crop, curious to relate, I have not been able to detect it in the samples of cane juice which I have up to now examined, but it must be understood that no systematic search for it has been carried out. But I have never yet failed to detect the presence in large quantity of some kind of bases or alkaloidal bodies in cane juice which I have heated with excess of lime, and I have so far never yet failed to detect them in greater or less quantity in Jamaica rum. The influence of these bases on the rum is to make it dry and harsh, and I should say, judging from personal experience, that the action of rum on the human system containing these bases in any appreciable quantity is not beneficial There seems very little reason to doubt, that it is the presence of these bodies which renders new rum almost undrinkable. Anyone who has had an opportunity of smelling  these vile compounds, when isolated from the more agreeable smelling constituents of rum, could hardly be in doubt as to the desirability of doing away with them if possible. But can this be done? There seems to me no doubt that it can.

If cane juice be tempered with gradually increasing quantities of alkali, starting say from an amount sufficient to produce neutrality, it will be found that these vile smelling substances can only be extracted when a considerable excess of alkali has been used, and that by using moderate quantities of alkali it is quite possible to set free the essential oil of rum, without setting free these vile smelling bases. It will thus be seen that the tempering of the liquor is of great importance, not only to the process of sugar boiling but also to the manufacture of rum. As a result of my experiments in this direction I am able to say, that whenever the liquor is tempered until it becomes of a deep fiery orange to a ruby red colour, that there is danger of these organic buses having been set free.

It would appear then that a moderation in tempering is an essential point in the preparation of a good drinking rum, inasmuch as it would tend to furnish a rum of a mild, soft character, devoid of that dryness and harshness due to the presence of these organic bases, and thus fitter for immediate consumption : though whether this would equally hold good in the case of German Rum, in which I believe as much “flavour” as possible is desired, may remain a disputed point. On the other hand, on estates with heavy badly drained clay soils, rather heavy liming is, I believe, found to be necessary, which probably stands in intimate connection with the destruction of the glucose, which would be found in larger quantity in canes grown on lands where all the conditions necessary to the thorough ripening of the cane were not present. Besides the effect on the flavour, these organic bases have a very disastrous effect on the fermentation. As the result of a large number of fermentation experiments, performed with No. 18 yeast, I have found this to be invariably the case, and this enables us to make a shrewd guess as to what would be the effect of such bases on the human system.

The yeast is in fact poisoned. The amount of lime then used in the tempering of the liquor may not only have an effect on the flavour of the rum, but also on the progress of the fermentation, and it does not seem at all improbable that some of the disasters of the Still House may be due to the treatment of the juice in the Boiling House. I hope, however, at some future time to be able to furnish some more definite and interesting information on this point.

Lime therefore exercises a potent influence both for good and evil. Thus indirectly, it sets free the fruity acid. While directly it sets free—
(1). The essential oil of rum.
(2). Various kinds of organic bases or alkaloidal bodies.

As regards the nature of the chemical reactions which take place, it seems to me that we can pretty well infer it from the nature of the reagent used, and of the substances set free. The only reactions which can take place as far as I am aware are those of hydration and interchange of lime for the volatile organic bases or alkaloids combined with acids. In tempering cane juice, which for this experiment may be most conveniently performed by an easily soluble fixed alkali, such as caustic soda, it will be found, if the alkali, be used with caution, that a gradual disappearance of the fixed alkali takes place as the heating progresses. In this respect it is instructive to compare the behaviour of the two indicators phenol-phthalein and litmus; the former showing us the gradual disappearance of the fixed alkali, while from the behaviour of the latter, we should imagine that the fixed alkali was still present in excess. That this is not so can also be proved by distilling the liquor, when the distillate will be found to behave exactly the same towards the two indicators, blueing litmus and having no effect on phenolphthalein-—due of course to the setting free of volatile organic bases, which have no effect on phenol-phthalein: it need hardly be said that this is not due to the liberation of ammonia. But whatever conclusions may be ultimately arrived at as to the exact nature of the chemical changes, and as to the nature of the products of such decompositions, it will not I think be denied by anyone who carefully goes into the matter that the tempering of the liquor in the Boiling House has a very decided influence on the aroma of the Rum. No one who examines the residues which result from the chloroform and ether extractions of cane juice, before and after the treatment with lime, can have a doubt of this while an examination of almost any rum, which has been manufactured in this country, using the aforementioned solvents, will enable him to discover the same smelling substances which can be extracted from treated cane juice. It is not of course contended that the whole of the aroma of Rum is due to this cause, but I do not hesitate to say that directly and indirectly a very considerable part of it is. And moreover in breaking fresh ground, as I believe I am in these researches, it was considered more important to attempt to localise the chief points of interest and to ascertain the actual facts of the case, rather than to dwell on the theoretical side of the question, which becomes of importance only in relation to facts. These researches too were commenced in the first instance with one object in view, viz to elucidate the nature of the action of N o. 18 yeast in producing its characteristic aroma. I very soon found that I was working in the dark on this very interesting question, and it is only now on having learnt the nature and the result of the action of temper lime on cane juice, that I am encouraged to believe that I have found the solution of this previously difficult problem. But of this more anon. It is obvious however that even the practical side of the question is far from being exhausted, and an ever broadening field of investigation is opened up. If one may be allowed to theorize a little, there seems sufficient grounds for concluding, from the results which I have up to now attained, that though the aroma of rum is in the first instance derived from the soil, that this influence is chiefly potential not actual; that it is latent, dormant, and only brought into existence during the process of manufacture. If this should prove to be the case, it would seem to hold out a hope that much may be done to improve our rums both for the home trade in England and for export to Germany ; and to imply a rebuke against murmuring with folded hands—“it’s the soil that does it.”