[This was quite a tedious chapter to translate. Keep in mind that the chemical formulas are limited by the wordpress editor. This chapter saw the introduction of “Bauer oil” and a large section on rum oil/terpenes with quite a few authors cited.]
Composition of Rhums
In addition to ethyl alcohol, eaux-de-vie contain secondary products generally referred to as impurities. If this term is appropriate when it comes to industrial alcohols, which are really contaminated by the foreign substances they contain, it is no longer the case for beverage alcohols, where the secondary products form the bouquet and determine the quality of the eaux-de-vie. The expression of non-alcohol, adopted by the 5th International Congress of Applied Chemistry, would be more adequate, but the use of the first term prevailed, at least in France.
Impurities belong to very different chemical functions: alcohols, acids, adehydes, bases, hydrocarbons, etc. Their nature and proportions, even for a given spirit, such as rum, are subject to important variations, hence the great diversity of bouquets.
To characterize an eau-de-vie chemically, it would be important to make qualitative and quantitative determination of non-alcohol. But this is a delicate and complex operation, which can only be performed by an experienced chemist with a well-established laboratory. It is also a long operation, requiring the implementation of a large quantity of the liquid to be examined, which is not very compatible with the requirements of the trade, which can not wait long for the results of the analysis and provides the chemist only samples of reduced importance.
Also, in current practice, it is enough to measure the impurities by groups, according to their chemical functions. Under the name of coefficient of impurities or non-alcohol coefficient, also called Lusson-Girard coefficient in some foreign countries, the sum of the volatile impurities: acids, aldehydes, esters, higher alcohols and furfurol, expressed in milligrams per 100 cc. of absolute alcohol contained in the analyzed eau-de-vie, or in grams per hectolitre of absolute alcohol. According to the International Convention for the Unification of the Presentation of Analytical Results, adopted by the International Conferences of June 27, 1910 and May 13, 1929 (1), acids are evaluated as acetic acid, aldehydes as acetaldehyde, esters in ethyl acetate and the higher alcohols in isobutyl alcohol or amyl alcohol, but indicating which of the two. It is also sometimes measured in the non-alcohol coefficient: organic bases (evaluated as ammonia), methyl alcohol and frequently, instead of only volatile acids, the total acids.
(1) Ann. Falsif. XXIV, 69, 1931.
In addition, determination is usually made of the dry extract, expressed in grams per liter of eau-de-vie, and sometimes that of ashes and coloring.
Ethyl alcohol, ordinary alcohol or ethanol, of formula C2H5-OH, is a colorless and very fluid liquid, of a spirit odor and a burning flavor. It has a density at 15° of 0.793634 and at 20° of 0.78933, the water at 4° being taken as a unit (figures adopted at the International Conference of Applied Chemistry held in Paris on June 13, 1929) (1). It boils at 78°3 C at a pressure of 760 mm and solidifies at about – 117° C. Its vapor pressure is 44 mm at 20°.
(1) As a result of the difficulties experienced in the dehydration of absolute alcohol, the author gives somewhat different figures for the density of alcohol. Winkler indicates the following values: 0.80629 at 0 °; 0.79787 at 10 °; 0.79363 15 °; 0.78937 20 °, the water at 4 ° being taken as a unit and the weighings brought back to the vacuum. The corresponding values found by Mendelejeff are: 0.80625, 0.79288, 0.79367 and 0.78945 respectively. Osborne, McKelvev and Bearce obtained as average density of 15 samples of the purest alcohol they could have prepared: 0.78506 at 25 °, the water at 4 ° being taken as unit.
Ethyl alcohol is slightly hygroscopic. It is miscible with water in all proportions. The mixture is accompanied by a release of heat which dilates the liquor and, after return to the original temperature, a contraction of the volume, which indicates the formation of a hydrate. The importance of this contraction depends on the relative quantities water and alcohol. It is maximum (3.7%), when 52 volumes of alcohol are mixed with 48 volumes of water. In addition to the latter hydrate, which contains 3 molecules of water for 1 molecule of alcohol, CH2-CH3OH + 3H2O, it has been reported the existence of 2 other hydrates of alcohol, one to 2 molecules of water; CH3-CH2OH + 2H2O and the other 6 water molecules: CH3-CH2OH + 6 H2O (Varenne and Godefroy) (2).
(2) C. R. CXXXVII, 993, 1903.
Ethyl alcohol forms with water a mixture with a constant boiling point (azeotropic mixture), when its proportion reaches 97.2% by volume (95.57% by weight) at 20 ° C. It forms analogous mixtures with benzine and other organic solvents.
Alcohol acts as a solvent on many organic substances: esters, essential oils, resins, fatty acids, etc. Neutral fats, with the exception of castor oil and croton oil, are poorly soluble.
At high temperature, the alcohol is burned completely by free oxygen, with a bluish, dimly lit flame; There is water production and carbon dioxide. One molecule (46 gr.) Gives off 325 calories.
At a lower temperature, the free oxygen acts on the alcohol, but only under special conditions (in the presence of platinum, for example, or certain ferments), by giving birth to acetic aldehyde, by simple loss of hydrogen, then with acetic acid by subsequent addition of oxygen. The oxidizing compounds act in a similar manner.
The alcohol reacts slowly with the aldehydes to give acetals.
In the presence of acids, it gives rise to ether-salts, with elimination of water:
The ether-salts derived from the hydrogenated acids are sometimes called simple ethers and those corresponding to the oxygenated acids, compound ethers. Other authors (Gerhardt) denominate simple ethers as ethers-oxides, formed by the union of 2 alcoholic molecules (we apply more specifically to them the term ether), compound ethers, the ether salts, they are derived from oxygenated or hydrogenated acids. Also, the expressions of simple ethers and compound ethers, which are confusing, are abandoned today. Congress nomenclature, to briefly call the ethers-salts, have taken the word ester, proposed long ago by Gmelin.
The monobasic acids give rise to neutral esters and the polybasic acids to neutral esters or to acidic esters, according to the number of ethyl radicals (C2H5) which replace the metallic hydrogen of the acid.
The proportion of ethyl alcohol found in rums is quite variable. The products shipped from the English colonies usually measure 78 to 81% of alcohol and those of the French colonies 60 to 65%. The alcoholic strength of rums consumed is usually between 40 and 50° G.L. Exceptionally, it can rise to 55° (French West Indies) or lower to 35°.
Higher alcohols are still designated, more particularly in foreign countries, under the name of fusel oil (fusel oil, fuselol). This term is confusing because it also applies commercially to distillation bottoms, which contain, in addition to higher homologues of ethyl alcohol, high-boiling bodies belonging to various chemical functions (acids , esters, hydrocarbons, etc.). It is also used to refer to amyl alcohol.
The methods of assaying higher alcohols leave much to be desired. Not only can the results obtained be far removed from reality, but they also vary from one to twofold depending on the method used (see Chapter XV). The data recorded in the technical publications with regard to these impurities are thus of very relative value and are comparable only in so far as the same mode of determination has been used.
Content of higher alcohols.
The amount of higher alcohols found in rums is generally between 100 and 300 gr. per hectolitre of pure alcohol. However, it can decrease significantly below 100 in some very light products and exceed 600 for barrel aged eaux-de-vie. The proportion of higher alcohols relative to other impurities, and in particular the value of the Higher Ac. : Esters ratio, also undergoes significant variations.
These variations are related to the conditions that preceded the rum production: composition of the must, type of fermentation, distillation method, aging.
The maximum values for young eaux-de-vie were recorded in the case of rums of battery syrup, obtained from musts with a large quantity of vinasse, without sulphate of ammonia, and having been the object of a fairly long fermentation (4 – 5 days). We have found in spirits of this type higher alcohol levels of 330 – 400 gr., With 25 – 36 gr. only esters (ratio Higher Alc. : Esters (11 to 16). When the fermentation of the must of vesou, aided by the addition of Am sulphate, is more rapid, the quantity of the higher alcohols decreases (generally from 100 to 200 gr.), as well as the value of the ratio Higher Alc. : Esters (1.2 to 4). It is this last balance that is usually observed in rums of cane juice from Guadeloupe, while the “grappe blanche” currently produced in Martinique are getting closer to rums of syrup.
[I don’t think batterie syrup implies molasses to Kervegant. I would not be surprised if many new American producers trying to make rums with dunder are using nutrients improperly and generating a lot of higher alchohols.]
Exceptionally, when cane juice, not containing added nutrients, is fermented for a relatively long time spontaneously, the number of higher alcohols may be less than 100 and the value of the ratio Higher Alc. : Esters smaller than unity (some rums from Madagascar and French Guiana). In the case of light, low-impurity rums, the level of higher alcohols also frequently falls below 100, but the ratio Higher Alc : Esters then remains larger than 1.
Similar variations are observed for molasses rums. When the fermentations are fast and relatively pure, the level of higher alcohols is generally between 100 and 200, and the ratio Higher Alc. : Ester’s greater than unity (Guadeloupe rums, Martinique type 1927, Réunion, Demerara, Cuba, etc.) Exceptionally, the number of higher alcohols may be less than 100 and fall to 65 – 70.
In rums obtained from molasses musts composed with high quantities of vinasse and subjected to long-term fermentation, the quantity of the higher alcohols is relatively small and the quotient Higher Alc. : Esters can be much lower than unity. French chemists who have examined the grand arôme rums of Jamaica and Martinique (Galion type) indicate very low levels of about 20 to 50 grams of higher alcohols and Higher Alc. : Esters ratios from 0.03 to 0.15. On the other hand, foreign chemists have found higher figures: Collingwood Williams, for example, using the Allen-Marquardt method, measured in the German rums of Jamaica 80 to 144 gr. of higher alcohols per hl. of alcohol at 100°, while Strunk, employing the Röse method, found for 238 samples of this rum, 238 and 302 gr. (expressed as amyl alcohol). If, as Von Fellenberg has shown, the higher alcohols of Jamaican rums consist mainly of normal butyl alcohol, they largely escape the colorimetric reaction on which the French method of analysis is based, and the figures found by the chemists who used the latter are therefore significantly inferior to reality. However, grand arôme rums have an Higher Alc. : Esters ratio much smaller than 1, the level of esters of these spirits being usually between 350 and 800 gr.
Between the grand arôme and the ordinary molasses rums with Higher Alc. : Ester ratios greater than 1, other intermediate rums are found, obtained by spontaneous fermentation of more or less long duration. The level of higher alcohols is usually between 100 and 150, and the ration Higher Alc. : Esters slightly less than unity. This type, very common formerly in the French West Indies, is still quite common in Martinique and the Comoros Islands. Some common clean rums from Jamaica also compare, but for them the ratio of Higher Alc. : Esters is usually lower. The fact, pointed out by Rocques in 1906, that ester-rich eau-de-vie from grapes were poor in higher alcohols and vice versa, is also generally observed in the case of rums, although there are quite a few exceptions to this rule.
It should be noted, for comparison, that the eaux-de-vie of Charentes and Armagnac wines have a higher alcohol content usually between 125 and 300 (150-200 on average) and a Higher Alc. : Ester ratio almost always greater than unity (1.2 to 3). The same is true of cider and perry, as regards the quantity of higher homologues. But here the ratio is usually less than unity, at least for real cider brandies, those derived from the rapid fermentation of apple juice (apple brandies of the United States) almost always having a ratio Higher Alc. : Esters smaller than 1. In marc spirits, higher alcohols can reach a very high figure (up to 350 – 400 gr per hl of alcohol at 100°) and hardly go below 150 gr. ; the ratio Higher Alc. : Esters is sometimes higher, sometimes lower than unity. This ratio is almost always less than 1 in kirschs, which contain a lot of esters (150 to 800 and more).
[Keep in mind with all this ratio talk, for the esters we know nothing of their own ratio of ordinary ethyl-acetate to extraordinary longer chain esters.]
During barrel aging, the relative content of higher alcohols substantially increases as a result of the concentration. Thus, we found 606 gr. higher alcohols in a vesou rum of Martinique aged 8 years and whose alcoholic strength had been lowered to 48°2; Valaer found, 666 gr. in a molasses rum from New England, kept 19 years in barrels (alcoholic degree 67°6); Lusson, found 612 gr. in a very old wine brandy. The Higher Alc. : Ester ratio increases or decreases, depending on the case, during aging.
[This New England rum would be the legendary preprohibtion rums from Felton & Son’s made under the direction of Harris Eastman Sawyer. These rums may not be palatable because of these higher alcohol numbers and would likely require blending down.]
Principal higher alcohols.
The counterparts of ethyl alcohol reported in spirits are:
[Keep in mind, these isomer molecule descriptions are limited by my text editor and cannot have subscripts.]
Propyl alcohol, C3H7OH. — There are two isomers: normal propyl alcohol and isopropyl alcohol. The first, or propanol-1. CH3.CH2.CH2OH, is a pleasant odor liquid, recalling that of ethyl alcohol, having a density of 0.804 at 20° and a boiling point of 97°4. By oxidation, it gives propionic acid. It is found in a large number of alcoholic liquids, mainly in the fusel oils of industrial alcohols (from which it is removed by fractional distillation) and in the various eaux-de-vie (grape marc, cognac, kirsch, etc.).
Isopropyl alcohol or propanol — 2. CH3.CHOH.CH3 is a colorless liquid, with a spirit odor, it boils at 82 ° and has a density of 0.785 at 20°. By oxidation, it gives acetone. Flanzy and Banos (1), operating by fractional distillation, have found it in the oils from the rectification of the spirits of wine, in the proportion of 20 gr. per liter of fusel. On the other hand, Metra, Lesage and Descatoire (2), who researched it by oxidizing the transformation of alcohol into acetone and characterizing the latter by a specific color reaction (modified Imbert reaction), could not find isopropyl alcohol in the various spirits that they examined (beet and molasses alcohol, spirits of wine, marc, cassis).
(1) C. R. CCVI, 218, 1938.
(2) C. R. CCVI, 1028, 1938.
Butyl alcohol, C4H9OH. — The most important of the four isomers of this alcohol are normal butyl alcohol and isobutyl alcohol.
Normal butyl alcohol or butanol-1, CH3 (CH2) 2.CH2OH, is a refractive liquid with an irritating odor, resembling that of amyl alcohol, but a little more vinous. It boils at 118° and has a density of 0.810 at 20°. By oxidation, It gives normal butyric acid.
Isobutyl alcohol, isopropylcarbinol or 2-methyl propanol-1, also called fermentation butyl alcohol. (CH3) 2,: CH.CH2OH, is a colorless liquid having an irritating odor, similar to that of normal alcohol, boiling at 108° and having a density of 0.805 to 17°. By oxidation it gives isobutyric acid.
These alcohols are found in higher or lower proportions in the fusels of most spirits and industrial alcohols. It is usually isobutyl alcohol that predominates. Normal alcohol is found only exceptionally in industrial phlegms (potatoes, corn, etc.) obtained by pure fermentation. It is the same for some brandies (cognacs), while in others (kirsch, rums), it may exist in larger proportions than isobutyl alcohol. Its presence seems linked to the intervention of microbes during the fermentation, which explains why it was more abundant formerly than today, where the pure fermentations tend to be more common.
[It is hard to say what phlegm means specifically because of other word choices Kervegant has made previously. I’ve been told it best implies stillage.]
Amyl alcohol, C5H11OH. — The most important of the eight possible isomers are the normal primary alcohol, isoamyl alcohol and normal secondary amyl alcohol, which accompany the ethyl alcohol in most of the fermentations where this one is present.
The primary amyl alcohol normal or penianol-1, CH3.(CH2)3.CH2OH, boils at 137° and has a specific gravity of 0.817 at 20°. By oxidation, it gives valeric acid.
Isoamyl alcohol or amyl alcohol of fermentation is a mixture, in varying proportions, of two physical isomers: one deviating left polarized light, active isoamyl alcohol, secondary butylcarbinol or methyl-2-butanol-1, C2H5.CH (CH3) .CH2OH; the other does not possess the rotatory power of isoamyl alcohol inactive, isobutylcabinol or methyl-3-butanol-1. (CH3) 2.CH.CH2CH2OH, the latter in higher proportions (4/5 on average). Isoamyl alcohol boils at 131° and has a density of 0.812 at 20°. By oxidation it gives ordinary isovaleric or valerianic acid.
The normal secondary amyl alcohol or methylpropylcarbinol (2-pentanol), CH 3 (CH 2) 2 CHOH.CH 3 boils at 118° and has a density of 0.182 at 20°.
The crude amyl alcohol found in alcoholic liquids is mostly formed by inactive isoamyl alcohol. In addition, there is active amyl alcohol, normal primary amyl alcohol and traces of methylpropylcarbinol. It is a liquid of oily consistency with strong odor and suffocating characteristic, hot flavor, poorly soluble in water, soluble in alcohol, easily drivable by water vapor.
[Fascinating that Kervegant says suffocating characteristic because I compare higher alcohols to a wraith that you breath in and penetrates your lungs deeper than ethanol.]
Amyl alcohol is the dominant element of the fusel of industrial spirits (potatoes, beetroot, wheat, maize) and many spirits: kirsch (8/10 of higher alcohols, according to Windisch), grape eau-de-vie (Morin), etc…
Hexyl alcohols, C6H13OH. — Normal hexyl alcohol or caproilic (hexanol-1), CH3. (CH2) 4.CH2OH is an oily colored liquid with a pleasant and aromatic odor, boiling at 157°, having a density of 0.819 at 20 °). By oxidation, it turns into caproic acid.
[My understanding is this oxidation of all these alcohols is theoretic, but it practice it cannot be expected. Higher alcohols do not oxidize and go away even after long aging.]
Discovered by Faget (1) in the residues of the distillation of marc spirits, normal hexyl alcohol was found in various fusel oils, but in small proportions. According to Trost (2), isohexyl alcohol, together with amyl alcohol, is the dominant element of the cognac fusel.
(1) C. R. XXXVII, 730, 1853.
(2) Annali Chim. Appl. XXV, 660, 1933.
Heptyl alcohols, C7H15OH. — The normal heptyl alcohol or enanthyl alcohol, CH3 (CH2) CH2OH, is an oily, colorless liquid with a very penetrating odor, insoluble in water and soluble in alcohol. Boiling point 175°: density 0.819 (at 23°). By oxidation, it gives oenanthylic acid. This alcohol has been found especially in marc spirits (Faget), cognac (Ordonneau) (3), etc…
(3) C.R. CII 317, 1886.
Octyl alcohols, C8H17OH. — Secondary octyl alcohol or caprylic (octanol-2), CH3CHOH. (CH2) 5.CH3, is an oily, colorless liquid endowed with a strong and persistent aromatic odor, insoluble in water, miscible with alcohol and ether. Boiling point 179 °. Density 0.823 at 16 °. It is found in the products of distillation of castor oil with potash.
Nonylic alcohols, C9H19OH. — Normal nonyl alcohol (nonanol-1), CH3. (CH2) 7.CH2OH, is a colorless liquid, of aromatic odor resembling that of citronellol, boiling at 213° and having as density 0.841 (at 0°). It gives by oxidation pelargonic acid.
Decyl alcohol, C10H24OH. — Normal or capric decyl alcohol (decanol-1), CH3. (CH2) 8.CH2OH, is a thick liquid, very refractive, sweetish flavor, unpleasant, boiling at 231° and having as density 0.830 (at 0° ). By oxidation, it gives capric acid.
Higher alcohols of rhum.
The authors who have dealt with this question have come to quite divergent conclusions as to the identity of the Rums’ higher alcohols.
Kreis (4) who observed that the higher alcohol content in Jamaican rum by the Komarowsky colorimetric method was significantly lower than that provided by the Röse volumetric method, concluded that this spirit, unlike the rums of other origin, was particularly rich in propyl alcohol.
(4) Chem. Ztg. XXIV, 470, 1910.
Von Fellenberg found, on the contrary, that the higher alcohols of Jamaican rum consisted essentially of normal butyl alcohol. In a rum of certain authenticity, he began by eliminating the foreign substances (aldehydes, terpenes, esters), which could distort the determination of the higher alcohols, then he made the determination of the latter by means of the method of Röse and that of from Komarowsky in parallel. He thus found by the first method 2% and by the second 0.25% of higher alcohols, expressed as amyl alcohol.
The author then calculated, based on the volume increases of chloroform in the Röse tube (determined for certain higher alcohols by Sell) and on the intensities of coloration (observed by itself for the same alcohols), which amounts of different homologs of ethyl alcohol represented the levels of 2% and 0.25% of amyl alcohol above. He obtained the following results:
The figures are comparable only for normal butyl alcohol. In all other cases, the quantities given by the colorimetric method are much lower than those of the volumetric method. It follows that the higher alcohols of Jamaican rum are mainly formed by normal butyl alcohol. However, since there is a slight difference between the Röse (3.51) and Komarowsky (3.76) levels, it is possible that normal butyl alcohol is accompanied by a small amount of normal propyl alcohol. On the other hand, there is no isobutyl or amyl alcohol, even in the proportion of 1% of normal butyl alcohol. Fellenberg was also able to verify that the coloration obtained with the rum examined corresponded exactly to that provided by a normal butyl alcohol solution. Propyl alcohol also gave a comparable hue.
[I have almost been compelled to learn wet chemistry methods for fusel oil, but I’m being completely talked out of it.]
Dr. Strunck applied the same procedure to the examination of 2 authentic Jamaican rums and 8 rum samples of undetermined origin from the German war stocks. He found the following numbers:
The figures provided by the Röse and Komarowsky-Fellenberg methods are approximately equal, if expressed in normal butyl alcohol, which confirms Von Fellenberg’s opinion. Since, however, the proportion of normal butyl alcohol determined by stirring with chloroform is a little higher for certain samples than that given by the colorimetric method, it is possible that these rums contain traces of amyl alcohol or isobutyl alcohol or more likely, small amounts of propyl alcohol.
The 1895-II sample is, however, a remarkable exception: the hue obtained is not comparable to that of the standard solution of normal butyl alcohol, but only to that of an isobutyl alcohol solution. The values found by the method of Röse and Klomarowsky indicate that this rum contains a high proportion of isobutyl alcohol, which may be accompanied by amyl, butyl and propyl alcohols.
Quantin studied higher alcohols using the fractional distillation method. Having rectified, on behalf of an importer, 85 hl. Martinique rum at 54°, consisting of a mixture of rums obtained by small producers (1), he made in a Savalle column a fractionation into 3 parts: head tastes (2.5 hl.), heart alcohol (45 hl. at 93°) and tail tastes.The head tastes contained all of the acetic ester, aldehydes and in general all substances boiling below 72°, the heart alcohol, was very pure, and contained only traces of esters and tail tastes, the author extracted, by fractional distillation, the following alcohols, whose quantities (in gr.) were reported per hectolitre of rum:
(1) These rums can only be rum de vesou, from what we know of the conditions of rum production in Martinique.
In another rum from Martinique (probably a molasses rum). Quantin found in gr. by hl. of eau-de-vie (2):
(2) It should be pointed out that the percentage of higher alcohols determined by the Rocques colorimetric method was only 152 gr.
Ragunatha Rao analyzed fusel oil from the distillation of cane molasses in India. He obtained, for 2 samples of fusel, the average centesimal composition below:
In addition to the above alcohols, Sikhibusan Dutt found hexyl alcohol and heptyl alcohol in fusel oils of the same origin.
According to Kumamato, Formosa cane molasses fuses are mainly formed by amyl alcohols. The author gives the following composition:
In addition to propyl, isobutyl, isoamyl and amyl alcohols, Swenarton has found, in the crude fusel oil derived from fermented molasses, alcohols of the hexyl, heptyl, octyl, nonyl and decyl series, probably the normal alcohol and the first two terms of each series having the same isomeric structure as the isoamyl and amyl alcohols. He found the presence of 3 decyl alcohols, one of which is probably a terpineol. In fractions with a higher boiling point than that of decyl alcohol, small quantities of alcoholic products with even higher molecular weight appear to exist.
Taira and Matsujima, in Japan, reported the presence, in the fractions of cane molasses fusels, high boiling point, secondary heptyl alcohol, CH3 (CH2) 4.CHOH.CH3 (methyl-n-amylcarbinol), secondary nonyl alcohol CH3 (CH2) 6.CHOH.CH3 (methyl n-heptycarbinol), phenylethyl alcohol, C2H5CH2CH2OH, and a sesquiterpene alcohol, which they termed saccharol.
The discrepancies that emerge from the above studies are undoubtedly due in part to the difficulties inherent in the identification and determination of higher alcohols, but also and above all to variations in the composition of the rums, attributable to the nature of the raw materials used, microorganisms involved in the fermentation and the distillation mode.
Variations of the same order also exist in the case of other eaux-de-vie. Claudon and Morin (1), for example, give the following percentages of the higher alcohols of 3 eaux-de-vie from the Charentes region:
(1) C. R. CIV, 1187, 1887 ; CV, 1019, 1887 ; CVI, 360, 1888.
Methyl alcohol or methanol, CH 3 OH, is a colorless, mobile liquid with a pleasant and ethereal spirit odor having a density of 0.814 at 0° (0.792 to 20°), boiling at 65°. It is miscible with water and alcohol in all proportions. Subjected to the action of oxidants, it gives methyl aldehyde, then formic acid. It is obtained in the impure state, under the name of spirit of wood or methylene, by the dry distillation of wood and as a by-product in the manufacture of acetic acid.
[I would love more information how it is a byproduct of making acetic acid. Synthetic acetic acid?]
The question of the presence of methyl alcohol in eaux-de-vie has been the subject of much controversy, because of the importance it has from a chemico-legal point of view. In many countries, methylene is used for the denaturation of industry alcohols. Improvements made to the rectification processes make it possible to separate impurities with an unpleasant odor that accompany methyl alcohol in the spirit of wood (especially acetone). Fraudsters can be tempted, when taxes on beverage alcohol reach a high figure, to regenerate the denatured alcohol to blend with eaux-de-vie. At the same time, total separation of methyl alcohol from ethyl alcohol can only be obtained with difficulty and by very expensive work. In case this product is not encountered normally in natural eaux-de-vie, its presence would therefore allow to conclude the fraudulent use of denatured and regenerated alcohol.
[The better separation of acetone is new information to me in the methanol saga.]
Methyl alcohol, which has a pleasant odor and seems likely to exert a small amount of favorable action on the bouquet of spirits too lavishly supplemented with industrial alcohol, has sometimes been intentionally added to beverage spirits, because of its lower price. At the end of 1911, in Berlin, a few dozen people died and several hundred were very seriously ill for drinking eau-de-vie made of 4/5 methyl alcohol (Scharmach trial).
In a communication to the Academy of Sciences of March 1889, Marcano (2) argued that the rum was differentiated from other spirits by the presence of significant amounts of methyl alcohol, the bad head tastes obtained in the distillation of raw cane alcohol being, according to him, “formed almost exclusively by methyl alcohol”. It does not indicate by which process it could identify methanol. As the methods used at that time were for the most part limited to the search for the impurities accompanying methyl alcohol in the spirit of wood, it is probable, as Prinsen-Geerligs points out, that Marcano was misled by this fact.
(2) C. R. CVIII, 955, 1889.
Prinsen Geerligs, in 1897, examined from the point of view of their methyl alcohol content, various tropical spirits: rice liquor, Batavia arak, rums of vesou, molasses rum of Jamaica, Cuba and Malacca, using the modified Riche and Bardy method. He was led to conclude that none of the studied alcohols contained methanol.
Trillat (1), in 1899, applied the method of measurement which bears his name to the study of a large number of alcoholic liquids: rum, arak, kirsch, absinthe, marc and lees spirits, cognacs , etc… He found the presence of methyl alcohol in several commercial samples, sold at low prices, especially in kirschs, absinthes and rums. But, as he could not find this alcohol in authentic samples of cognacs and rums from Jamaica and Martinique, he concluded, according to the generally held opinion at the time, that the presence of methyl alcohol in the eau-de-vie was due to fraudulent addition of denatured alcohol. On the other hand, he found that a certain number of authentic marc brandies contained methanol, in a proportion estimated at about 0.25%. “The fact that the marc spirits did not all contain methyl alcohol,” he wrote, “shows that it is not necessarily there. Perhaps one could attribute its presence to a faulty distillation.”
(1) C. R. CXXVIII, 438, 1899.
Quantin, in 1900, confirmed Trillat’s and Geerligs’ conclusions with regard to authentic rums. All the tests that he carried out to characterize, by the Trillat reaction, methyl alcohol in the head tastes resulting from the industrial distillation of a mixture of rums from Martinique, gave absolutely negative results, after and before saponification of esters. The author concludes that the test product contained neither methyl aldehyde nor methyl alcohol nor methyl formate.
In the same year, Wolff (2), using the Trillat method perfected by him, encountered methanol in grape spirits, various fruit spirits (plums, mirabelle plums, cherries, apples) of genuine provenance and, even in trace amounts, in cognacs. On the other hand, rums, spirits and whiskeys examined by the author did not contain methyl alcohol.
(2) C. R. CXXXI, 1323, 1900.
[Did they yet know methanol was a product of the breakdown of pectin?]
Since then, many authors (Buchka (3), Bauer and Engler (4), Takahashi (5), Fellenberg, Reif Valaer (6), Ionesco-Matiu and Popesco (7), etc.) have confirmed the presence of Methyl alcohol in the most diverse alcoholic liquids: rice, wine, fruit spirits, rums, etc.
(3) Chem. Ztg. XXXVI 1309, 1912.
(4) Chem. Ztg. XXXVII, 328, 1913.
(5) Chem. Zent. 1904, 1476, ; 1909, II, 642.
(6) Ind. Eng. Chem. XXX, 339, 1939.
(7) J. Pharm. Chim. XXXII, 63, 1930.
According to Von Fellenberg (8), who used the modified Denigès method for the determination of methanol, the level of methyl alcohol normally reaches a maximum of 1% of total ethyl alcohol. However, in grape marc and fruit spirits it may be as high as 4% or more. Reif (9) found in methylated spirits of fruit and grape marc methyl alcohol levels ranging from 0.6 to 1.8% of absolute alcohol.
(8) Mitt. Lebensm. Hyg. V, 172, 1914 – Bioch. Z. LXXXV, 45, 1918.
(9) Z. Unters. Lebensm. LIII, 168, 1927.
[My understanding is that they eventually figured out you can produce grappa from grape pomace and be okay, but you cannot produce grappa from apple pomace because it has substantially more pectin and thus methanol risk. Unsound fruit should never be used.]
As regards the special case of rum, Siber (quoted by Von Lippman) (10), examining, in 1921, 20 different samples of head fractions obtained in the West Indies, found that in 2 cases the presence of methanol was doubtful, but that in the others the proportion of this alcohol varied from 1 to 8.5%: 2 samples contained from 1 to 2.5%, 7 from 2.5 to 5%, 5 from 5 to 7.5% and 3 from 7.5 to
8.5% methyl alcohol.
(10) Biochem. Z. CVI, 236, 1920.
[My understanding is that methanol can be present in rums if bagasse is mistakenly present in the molasses. I’ve only heard this anecdotally and I’m not aware if adding fine baggasse to stuck a fermentation has any bearing on methanol formation.]
The contradictory results obtained by the various authors are due mainly to the imperfection of the methods of research and dosage of methyl alcohol, based on the prior formation of the methanal by oxidation and the characterization of this aldehyde by colorimetric method. According to Flanzy, who has made a systematic study of these methods, the conversion of methyl alcohol to methyl aldehyde would never occur with a total or even constant yield. The colorimetric methods would finally allow us to appreciate a quantity of methyl alcohol usually representing a small part of the original quantity.
By applying a new micro-assay method that revealed uncertainties inherent in colorimetric processes, Flanzy was able to detect the presence of methanol in all the natural alcoholic media examined. The methyl alcohol content would vary from one alcohol to another and would clearly distinguish the different categories of spirits.
Regarding rums, Flanzy analyzed 15 commercial samples belonging to 3 different brands:
Note that Von Fellenberg (quoted by Guillaume) found, using the modified Deniges method, only 0.1 cc. (i.e. 80 mg) of methanol per liter of alcohol in a vesou rum from Martinique, and 0.3 cc. (240 mgr) in a molasses rum of the same origin.
[Telling the complete story of methanol in spirits will be very important for legalizing home distillation. The specter of prohibition still looms in the U.S.]
The content of aldehydes in rums is low: it usually varies from 10 to 40 gr per hl. pure alcohol. However, there are products that contain only traces or not at all of aldehydes: this is the case, for example, in some light rums of Cuba (Valaer). Exceptionally, Auffret was able to find up to 155 gr. in a molasses rum from Guadeloupe.
The various beverage alcohols generally comparable to rum with respect to the aldehydes. An exception must be made, however, for marc eau-de-vies, the content of which usually varies between 100 and 300 g. An excess of aldehydes would give the eaux-de-vie a bitter taste.
There does not seem to be any correlation between the type of rum and the content of aldehydes. These increase or decrease during aging, according as originally they were in low or relatively high proportions. Most often, in old rums, the aldehyde content does not exceed 40 gr. per hl, alcohol at 100°.
Some artificial oxidation aging processes give rise to considerable quantities of aldehydes. Chauvin, treating rum with hydrogen peroxide, found that the level of these impurities had risen from 146 originally to 1256. Subsequently, the aldehydes are also oxidized in turn and converted into acids.
The following aldehydes have been reported in the spirits:
Formic aldehyde or methylaldehyde, HCOH — Formic aldehyde, also called formaldehyde or methanal, is a colorless gas with a characteristic and very irritating odor, soluble in water. Its aqueous solution, at 40 or 45% aldehyde, is known commercially as formalin. Density 0.815 at -21°. Farnsteiner (1) reported the presence of methanal in alcohols, wine spirits and various spirits. Small amounts of this aldehyde could also be introduced by the caramel used for coloring. Trillat (2) found in various caramels examined by him methanal rates ranging from 0.005 to 0.325%.
(1) Ber. lib. Lebensm. u. ihre Bez. z. Hyg. IV. 8, 1897.
(2) Bulli Ass. Chim. XXIII, 652, 1905.
[Formalin is used as an antiseptic.]
Acetic or ethyl aldehyde, CH3 COH — Acetic aldehyde, acetaldehyde or ethanal, is a colorless, highly mobile liquid with a characteristic, pleasant but strong and suffocating odor, having a density of 0.788 at 16° C and as a boiling point 21° C. It is miscible with water, alcohol and ether. It oxidizes easily giving acetic acid.
Acetic aldehyde constitutes the major part of the aldehydes of eaux-de-vie and industrial alcohols. It accumulates, in considerable quantities, in the head products obtained in the distillation of alcoholic liquids.
The aldehyde acetic polymerizes, under very different influences and with a particular facility, by giving two polymers, paraldehyde and the metaldehyde, whose presence in the raw alcohol is reported (Kekulé).
The paraldehyde, which probably results from the condensation of three molecules of aldehyde, is a clear liquid, with a pleasant odor and with a burning taste, having a density of 0.994 (at 20°) and boiling at 124°. Not very soluble in water, soluble in alcohol and ether. Its vapor dissociates by heat regenerating the aldehyde.
Metaldehyde, which is formed at low temperature, is a solid body, depositing itself in the form of small white needles, insoluble in water, not very soluble in alcohol and in ether, sublimable without prior fusion towards 112-115°, partially regenerating the aldehyde.
Aldehyde combines with alcohols to give acetals. The ordinary acetal, ethyl acetal or diethylacetal CH3.CH: (OC2H5) 2, was found in charcoal-filtered alcohol (Geuther), the wine spirits (Ordonneau (3), Trillat (4 ), crude alcohols (Kraemer and Pinner (5). The aldehyde and the alcohol appear to combine cold, during the conservation of the eaux-de-vie, to give the acetal after a few months. This is a colorless liquid, with a particular sweet smell, fresh flavor with a nutty aftertaste, having a density of 0.831 (at 20°), boiling at 104°, slightly soluble in water, miscible with alcohol and ether.
(3) Bull. Soc. Chim. XLV, 332, 1886.
(4) C. R. CXXXVI, III 1903.
(5) Ber. Deut. Chem. Ges. II, 401. 1868.
Œnanthylic aldehyde or œnanthol, CH3.(CH3)5.COH — Colorless, highly mobile liquid, with a penetrating smell that is not unpleasant, initially sweet, then pungent, boiling at 156° and having a density of 0.823 at 15°. Very slightly soluble in water. This aldehyde has been reported in wine spirits.
Acrylic Aldehyde or Acrolein, CH2: CH2COH — Acrolein is a colorless, highly refractive liquid with a characteristic irritating odor and a burning taste. It is soluble in water and in alcohol, boils at 52° and has a density of 0.841 at 20°.
Normally absent from well-prepared spirits, acrolein has often been encountered in defective eau-de-vie: whiskey (Thorpe, Barbet), wine eau-de-vie (Barbet) and cider (Warcollier), rum (Bettinger), etc. It gives the product a characteristic pungent odor, which makes the alcohol almost undrinkable when its proportion reaches 1 / 10,000.
[Wow, I have never heard “undrinkable”!]
It is formed by dehydration of glycerine during fermentation or distillation. Some authors have attributed this dehydration to the intervention of microbes. Thus, Voisenet (1) isolated from bitter wines Bacillus amaracrylus, which, grown in the presence of glycerin, gives birth to acrolein. Warcollier, Le Moal and Tavernier (2) found in ciders containing acrolein a similar bacterium which develops mainly in a neutral medium and attacks the glycerin at the end of fermentation, when the sugar begins to fail; a high temperature favors its development. According to Bauer (3), on the other hand, acrolein comes mainly from the decomposition of glycerin in the distillation column. Whatever the case, its formation is favored by the high temperatures of fermentation and distillation.
(1) C. R. CLI, 518. 1910 ; CLIII. 898, 1911: CLVI. 1181, 1912.
(2) C. R. CXCIV, 1394, 1932 ; CXCVIII. 1546, 1934.
(3) Proc. 7. Int. Cong. Appl. Chem. 1909.
[Acrolein is likely a big risk for Arroyo style rums that use a fairly high pH.]
Acrolein in its pure state is very unstable: it oxidizes easily by giving acrylic acid; polymerizes in the long run, with formation of odorless disacryl; which with alcohol gives acrylic acetal, a form in which it is found partly in bitter wines; and finally resinifies under the action of acids or alkalis (Voisenet). It disappears accordingly gradually during the aging of spirits.
However, according to Barbet (4), mixed with alcohol, with which it associates itself closely, acrolein would be destroyed very slowly. The author has encountered it in significant proportions in whiskeys kept in barrels for two years and in Algerian wine spirits having spent three years in cask. Moreover, it is very difficult to separate from alcohol by rectification: only pasteurization gives results. Chlorine and hyposulphite of soda do away with the odor of acrolein, especially when the alcohol is at a high degree: but if the product thus deodorized is subjected to distillation, the odor reappears almost entirely in the distillate. It is important, therefore, to do everything possible, by properly acidifying the musts and by preventing an excessive rise in temperature, so that the acrolein can not take birth.
(4) C. R. 2. Cong. Int. Chim. Appl. I, 464, 1896.
Pyromucic aldehyde or furfurol C4H3O.COH — Furfurol is a colorless (but black on contact with air) liquid, with an odor reminiscent of both bitter almond and cinnamon, with a density of 1.159 at 20°, boiling at 162° , slightly soluble in water, very soluble in alcohol.
[I find the aroma to be very stale like wet cardboard.]
Many rums (grappe blanche of Martinique, Cuban rums, Demerara) do not contain furfurol, or contain only traces. In some cases, on the contrary, the rate of this impurity may exceed 10 gr. per hl. of absolute alcohol. An average content is that of 1-2 gr.
[Dont’ forget, it is characteristic of pot distillation (and extended time under heat) and can imply how much pot spirit is in a blend.]
Furfurol originates mainly during distillation, by the prolonged boiling, with water, of certain carbohydrates: the acidity of the environment favors its production. Also, high levels of furfurol are found in spirits obtained from dense musts, which undergo high temperature for a longer time to yield their alcohol (rums full of Martinique). The use of intermittent distillation apparatus, heated by open fire, where roasting of organic matter suspended in the wine can take place, also increases the level of furfurol in the distillate (Jamaican rums). Moreover, the caramel used for coloring can bring small amounts of furfurol, especially if the caramelization has been done at high temperature (around 200°).
During barrel aging, the wood gives furfuroides to the eau-de-vie. The quantity of these, low or zero when the cask has already been used for housing spirits, may be relatively high in the case of new containers, not previously broken in. Thus, Valaer cites the case of a Kentucky molasses rum, distilled in an intermittent still, whose furfurol rate, originally 10.5 gr, had passed, after 2 years of storage in charred oak barrels at 22.5 gr. per hl. of absolute alcohol. These figures are however quite exceptional, and most often the gain in furfurol is only 1 or 2 gr in the first years. If storage is prolonged, the rate of furfurol tends to decrease, especially when the eau-de-vie is kept in bottles.
Vanillin C8H8O3 — Vanillin, also called vanillic aldehyde or methylprotocatechic aldehyde, which is the methyl ester of protocalechic aldehyde, is a solid body, crystallizing in colorless needles, grouped into stars, fusible at 81° and sublimated at a temperature higher, boiling at 285°, in an atmosphere of carbon dioxide. It has the characteristic smell of vanilla and a pungent flavor. Soluble in water and very soluble in alcohol, ether, carbon disulfide.
Vanillin is often added intentionally to give a bouquet to imitation brandies (particularly rum). But it is also normally found in spirits that have stayed in wooden barrels. They contain, indeed, small amounts of vanillin, which are dissolved by alcohol. According to Reif (1), the content of spirits in vanillin (10 and 20 mgr per hl of eau-de-vie respectively for the alcohols and wine spirits examined by the author) depends on the relative surface area of the wood, the length of storage in the cask and, to a certain extent, the degree of alcohol.
(1) Z. Unters. Lebensm. LIV, 90, 1927.
Vanillin would be met too, at the same time as eugenol in some raw alcohols, and would come in this case from the raw material. E. Bauer (2) and M. Karcz (3), for example, reported the presence in alcohol from beet molasses of eugenol and coniferyl alcohol, a decomposition product of vanillin. According to Karcz, this last alcohol would be found in beets in free form or in the form of a glucoside (coniferine), which during fermentation would be broken down into coniferyl alcohol and glucose. Part of the coniferyl alcohol would given by eugenol reduction.
(2) Chem. Zts. XII, 629, 1888.
(3) Chem. Ztg. XII, 629. 1888. [Not sure if these being the same is a typo.]
The content of the rums in total free acids varies within wide limits. Girard and Cuniasse have found up to 400 grams in a rum from Martinique, while for light rums from Cuba, the acidity can drop to 5 grams, according to Valaer.
Spirits contain volatile acids, formed during fermentation or aging, and fixed acids consisting for a small part of the fixed acids of the must entrained during the distillation, and especially by the principles extracted from the wood during aging in barrels and by the various products added to the spirits (sauces, etc.). In industrial alcohols, on the other hand, the free acidity is composed entirely of volatile acids.
The share of fixed acidity in the total acidity is very variable. There is no or very weak fixed acidity when spirits have just been distilled but can be as high as volatile acidity after prolonged aging in barrels or addition of sauces. Most often, however, it remains substantially below the latter.
The acid content is closely dependent on the type of rum and the duration of aging. Ordinary rums of vesou and molasses, obtained by fast fermentation, have a relatively low level of acids when they have just been manufactured: 30 to 50 gr on average. The figure can go down to 12-15 gr in rums de vesou and rise in some cases to 100 gr, but rarely above. The grand arôme rums of Martinique have a content ranging from 200 to 300 gr. Those in Jamaica have a lower coefficient of free acids, very rarely greater than 150 grams, but the amount of the combined acids (esters) is very high. Moderately heavy molasses rums, prepared from must having high proportions of vinasse, usually have a free acidity of 100 to 200 gr. per hectolitre of pure alcohol.
[Fascinating. Jamaica is very successful at making esters of the volatile acids they collect in their hearts fraction. Because of the nature of equilibrium, they may loose many esters during maturation. How they adjust to equilibrium is something we need to learn more about.]
During aging in casks, the acidity of eaux-de-vie increases rapidly. Valaer was able to observe that after a 2-year stay in warehouses in the United States, the volatile acid content of rums, in some cases, could quadruple and even quintuple. In Martinique, we observed rums de vesou, whose measure of total acids, in the order of 15-20 grams originally, increased to 300 grams and more, after 6-8 years of storage in the colony.
[Incredible details and the last anecdote pertains to tropical aging. What we see is evidence that ethyl acetate likely does not blow off. This is a big weakness of the grand arôme rums. If they want to age grand arôme marks, they would have to blend down their ordinary ethyl acetate esters first. My understanding is that Hampden is doing this. They had to develop a pot still low ester rum.]
The eau-de-vie of wine, fruit and grain, when just made, generally have a less variable acidity than that of the rums, the processes by which they are obtained being more uniform. In new Charentais spirits, for example, the acids oscillate between 4.8 and 48 according to Rocques. The rate rises gradually during aging and can reach up to 400 (very old brandy believed to be more than 80 years old, analyzed by Rocques). The acids generally vary from 50 to 100 for cider and perry brandies, from 75 to 250 for kirsch, and from 30 to 200 for marc spirits.
The following acids have been reported in brandies and industrial alcohols:
Formic acid, H.COOH — Formic acid is a colorless, very clear, caustic liquid with a very irritating, special odor. It has as density of 1.220 at 20°; boils at 100°8 and is miscible with water and alcohol in all proportions.
Formic acid exists in rums and araks in the free state and in the form of ester: it is characteristic of these eaux-de-vie. Sell (1) measured, in rums of various origins, 3 to 12 gr. of free acid and 8 to 23 gr. ethyl formate per hectolitre; Windisch (2) found 3 to 14 gr. of free acid and 9 to 26 gr. of formate. The rums of Demerara (old type) were particularly rich in formic acid: the maxima indicated by the above authors relate to products of this origin, while Miller (3) found for various rums of the same origin 8.8 to 40.5 gr. of ethyl formate per hectolitre of eau-de-vie. Quantin found 9 grams of formate per hectolitre. of eau-de-vie in rums de vesou of Martinique.
[I’ve translated a contemporary study on formic acid from the great INRA team in Martinique.]
(1) Arb. Kais. Gesundh. VIII. 210, 1891.
(2) Arb. Kais. Gesundh. VIII. 257, 1893.
(3) Timehri IV 90, 1890. [This is a Guyanese journal and may be worth hunting for to learn more about their “old type”.
According to Fincke, the determination of formic acid would make it possible to differentiate original Jamaica rums from rums blended with neutral alcohol and imitation products. This author found in 6 authentic Jamaica rums 4.4 to 6.9 free formic acid and 3.5 to 4.7 gr. of acid esterified per hl. alcohol. For 6 blended rums the proportions fell to 0-44 and 0.8 respectively, while for 7 rums of imitation they amounted to 8.8-62.4 gr and 0-6.8 gr.
Acetic acid, CH3COOH. — Acetic acid is a colorless liquid, with a strong, irritating odor and a strong acidic taste. It has a density of 1.050 at 20°, boils at 118° and solidifies at +16°7. Soluble in all proportions in water and alcohol.
This body, which is derived from ethyl alcohol by oxidation, is the most important element of the group of acids existing in spirits.
Propionic acid, CH3CH2.COOH. — Oily liquid with a smell of sour cabbages, having a density of 0.992 at 20° and boiling at 141°. It is soluble in water in all proportions.
Butyric acids C3H7.COOH. — Two isomeric butyric acids are known: normal butyric acid and isobutyric acid.
The first also known as butyric acid of fermentation CH3(CH2)2.COOH is an oily, colorless liquid with an unpleasant odor reminiscent of rancid butter, with a very acidic and hot flavor. It has a density of 0.964 at 15° and boils at 163°. Miscible with water, alcohol and ether. Butyric acid originates in the fermentation of carbohydrates under the influence of various microbes. It is found more particularly, in the free or esterified state, in spirits obtained by impure fermentations. It has been reported in wine spirits (Claudon and Morin, Wüstenfeld and Battay), rums and araks (Windish, Kayser, etc.).
Isobutyric acid, (CH2) 2: CH.COOH, which results from the oxidation of isobutyl alcohol, is a colorless liquid with a less unpleasant odor than that of the normal acid. It has a density of 0.950 at 15°, boils at 155° and is less soluble in water than its isomer.
Valeranic or valeric acids C4H9COOH. — The most important of the 4 isomeric valeranic acids is isovaleranic acid or methylbutanoic acid, (CH3)2: CH.CH2COOH, which originates in the oxidation of isoamyl alcohol. It is a colorless oily liquid, with an unpleasant smell reminiscent of valerian and rotten cheese, with an acid and hot taste, having a density of 0.942 at 20° and boiling at 176°.
Normal hexyl acid or caproic acid, CH3. (CH2) 4.COOH, — Colorless, oily liquid, with an unpleasant smell reminiscent of sweat, with a density of 0.945 at 0°, boiling at 205°, slightly soluble in water, but soluble in alcohol. As a by-product of butyric fermentation, caproic acid has been reported, in the free state and ester form, in eaux-de-vie by various authors (Windisch, Sell, etc.).
[I have smelt beautiful sweating aromas in the later birectifier fractions. They are never overpowering, but just present enough.]
Normal heptyl acid or œnanthic acid, CH3. (CH2) 5.COOH. — The oily, colorless liquid, with a weak odor reminiscent of that of cod and very acidic flavor, having a density of 0.935 at 0 °, boiling at 223°. Its presence has been reported in the eaux-de-vies of wine (Ordonneau), rice, corn, etc.
Normal octyl acid or caprylic acid, CH3. (CH2) 6.COOH. — Colorless liquid, not aromatic when cold but with a weak sweat odor which develops hot, crystallized by cold in fusible slats at + 14°. It has a density of 0.910 at 20° and boils at 237°. Not very soluble in water, soluble in alcohol and ether. It occurs in various fermentations: it is found in particular in certain cheeses, putrefied yeast, in the bottoms of the distillation of various alcoholic liquors.
Normal nonyl acid or pelargonic acid, CH3 (CH2) 7.COOH. — Oily liquid, with a weak butyric odor, having a density of 0.911 at 12° and boiling at 260°. It is crystallizable by the cold and then melts at + 12°5. Its presence has been reported in various eaux-de-vie and fusel oils (Ordonneau, Windisch, Perrot, Luce). It would be particularly abundant, in the form of ethyl ester, in the beet molasses fusels (Ordonneau).
Normal decylic acid or capric acid. CH3.(CH2)8.COOH. — Crystalline substance, colorless, of a slight odor of butter (especially accentuated under hot conditions), melting at 31° and boiling at 270°, having as density 0.930 at 37°. Insoluble in water, soluble in alcohol. It has been encountered in many fusel oils: corn (Rowney (1), Hilger (2), wine (Windisch, Grimm (3), potatoes (Johnson (4), cane molasses (Marvel and Hager), etc.
(1) Ann. IXXIX. 236. 1851.
(2) Chem. Zent. 1894, I, 281.
(3) Ann. CLVII, 267, 1871.
(4) J. prait. Chem. LXII, 261, 1854.
Normal duodecyl acid or lauric acid, CH3. (CH2) 10.COOH. — Crystalline substance in the form of needles melting at 43°, boiling at 225° under 100 mm. pressure, volatile with water vapor, having a density of 0.883 at 20°; insoluble in water, soluble in alcohol and ether.
Grossfeld and Miermeister found the presence of lauric acid in the various alcoholic beverages they examined: wines, beers, spirits. The lauric acid content is not proportional to the alcoholic concentration that: from 32.6 to 57.7 mgr. per liter of pure alcohol for the eaux-de-vie studied (spirits of wine, grain, rum), it reached 183.4 in a red wine from Spain and 702.9 mgr. in a beer. Since this acid is a characteristic element of the distillation bottoms, the spirits contain more or less large quantities depending on the distillation method: the rectification makes it possible to eliminate it completely (especially in the trois-six surfins). According to the authors above, the essence of cognac (5) consists mainly of lauric acid and not of capric acid as previously thought (Fischer).
(5) The essence of cognac, also called the essence of grapes, wine, lees, etc., is obtained by distilling the lees of wine. Considered by ancient authors as constituted by oenanthical ether, it is actually a mixture of fatty acids with high molecular weight, free or esterified (Ordonneau).
[still not sure what trois-six surfins implies]
Normal tetradecyl acid or myristic acid, CH3. (CH2)12.COOH. — Solid substance, in the form of white crystalline lamellae, with a silky luster, resembling those of palmitic acid. It melts at 53°8 and boils at 250° C. under the pressure of 100 mm. Its presence in cane molasses fusels was reported by Taira and Matsujima.
Normal hexadecyl acid or palmitic acid, CH3.(CH2)14.COOH. — Solid substance, presenting itself after having melted and solidified, in the form of a colorless crystalline mass, lamellous, less dense than water, tasteless. It melts at 62° and boils at 271°5 under the pressure of 100 mm. It is distilled by a stream of superheated steam. Insoluble in water, soluble in alcohol and ether.
Palmitic acid, which constitutes, in the form of glycerol ester, an important element of animal and vegetable fats (especially palm oil), has been found in many fusel oils: potato fusel (Shorigin, etc. (6), potato (Yoshitomi, etc. (7), cane molasses (Kino (8) corn (Baker and Barkenbus), Mulder, in 1858, already reported the presence of palmitic acid in rum.
(6) Ber. Deut. Chem. Ges. LXVI – B, 1087, 1933.
(7) J. Pharm. Soc. Japan 1922, 486.
(8) J. Soc. Chem. Japan XXXI. 749 1928.
Acids of rhums.
In his experiments on the fermentation of sugar cane molasses, Kāyser found the formation of formic, acetic and butyric acids. He admitted that the rums also contained propionic acid and, in some cases, valerianic acid. The method of determination used (Duclaux’s method), however, leaves some uncertainty as to the presence of these latter acids. The same author has observed the production of formate, acetate, butyrate and ethyl valerianate, the proportion of these different esters varying with the race of yeast, the composition of the medium, the temperature of fermentation.
Windisch and Sell admit the presence of formic, acetic, butyric and caproic acids in rum, accompanied by their ethyl esters. They obtained for various rums originating from Jamaica, Cuba and Demerara, the following quantities in these various elements (gr per hectolitre):
According to Grossfeld and Miermeister, what Windisch regards as caproic acid and ester is actually a mixture of various high molecular weight acids and esters (caproic, caprylic, capric, lauric).
Allan and Ashby found that Jamaican rums contained the following acids (free or esterified): acetic, propionic, butyric, caprylic, capric and lauric. According to Cousins, ethyl acetate would form about 97% of the total esters of German flavored rums, the rest being 2% ethyl butyrate and 0.5 to 0.8% high molecular weight esters, sometimes with traces of ethyl formate. In Cognac eaux-de-vie, 92% of the total esters, according to Ordonneau, are also ethyl acetate.
Taira and Matsujima, Japan, observed the presence of caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, oleic acid, linoleic acid and linolenic acid in cane molasses, but they did not find and pelargonic.
Marvel and Hager reported that by rectifying 65° eau-de-vies made with cane molasses in Cuba, an oily, dark amber colored liquid was obtained on the lower tray of the column, with an unpleasant odor, very penetrating reminiscent of that of pyridine. This oil, which has been referred to as Bauer oil and is normally found in molasses rums when they are distilled without the extraction of fusel oil at the column, represents only a small proportion of the original spirit: 1 liter per 100,000 l. eau-de-vie. After fractional distillation, 1 liter of Bauer oil gave the following fractions (under 6 mm pressure):
[Noticed these are other researchers naming this product after bauer whose name comes up quite a bit in this chapter. I bet there are some good papers to find.]
[Fascinating, their take the oil and vacuum distill it noting the volume accumulated per range in boiling point.]
The boiling points of the 4 main fractions (100°-105°, 129°-134°, 149°-154° and 174°-180°) correspond well to those of the ethyl esters of capric, lauric, myristic and palmitic acids. It has, moreover, been possible to isolate these acids in the pure state and to identify them by their physical constants. The intermediate fractions are undoubtedly constituted by a mixture of caprate, laurate, myristate and ethyl palmitate. Alcohols other than ethyl alcohol were not found. Marvel and Hager were able to obtain, by distillation of one gallon of Bauer oil, 650 cc of ethyl caprate, giving after saponification 70% of capric acid.
[Keep in mind, these were not described as smelling good, but that is because they are in a too concentrate state and not supported perceptually by ethyl acetate. Bauer oil is a term I will have to find more background on.]
In summary, the volatile acids of rum, in the free or esterified state, would be constituted for the most part by acetic acid, with more or less important quantities of formic and butyric acids, and small quantities of acids of high molecular weight: caproic, caprylic, capric, lauric, palmitic, etc.
Rums of vesou and those of molasses obtained by rapid fermentation have a level of esters usually between 30 and 100 gr per hectolitre of absolute alcohol. This figure may however decrease in some cases to 12 gr.
The grand arôme rums of Jamaica contain the highest quantities of esters. They sometimes measure 1500 gr of esters, according to Cousins, and rarely less than 400 gr. Wüstenfeld and Luckow report having encountered samples that contained more than 2,000 and up to 3,081 gr. The “grand arôme” of Martinique is characterized by a much lower rate of esters (300 to 500 ordinarily).
Medium-bodied rums of molasses have an intermediate richness between those of light rums and “grand arôme”: 100 to 200 gr on average.
The observations made in France on the eaux-de-vie of Charentes indicate that the proportion of esters varies little during aging (Lusson, Rocques). The increase is apparent and due almost entirely to the reduction in alcoholic strength. However, it may be different, when the conditions of conservation are different. Valaer, in the United States, observed that after 2 years of storage in charred oak casks, the esters of rums could in some cases be more than doubled. Crampton and Tolman, also in the United States, found that whiskeys, after 4 years of storage in barrels, saw their ester levels triple or quadrupled. We ourselves observed in Martinique, that rums of vesou, measuring at the origin 30 to 40 gr of esters, contained 120 to 150 gr after 7 or 8 years of aging.
[If Cognac differed, it could be because their barrels were so exhausted as not to contribute ethyl acetate. These other examples likely only saw increases in ethyl acetate due to the influence of the wood.]
For beverage alcohols other than rums, the ester content generally varies between the following limits:
The following esters have been found in spirits and alcohols:
Ethyl formate or ethylformic ester, HCO2 .C2H5 — Colorless liquid, with a strong rum odor, having a density 0.906 at 20° and boiling at 54°. It dissolves in 9 parts of water at 18°. Because of its special fragrance, ethyl formate is often used in the preparation of artificial bouquets of rum.
Ethyl acetate or acetic ester. C2H3O2.C2H5 — Colorless, clear liquid with a clean, refreshing odor. It has a density of 0.900 at 20° and boils at 76°. Soluble in 17 parts water at 17° and in all proportions in alcohol and ether. This is the dominant element of the esters of eaux-de-vie.
Butyl acetate. C2H3O2.C4H9. — Normal butyl acetate is a colorless liquid, not very mobile, with a pleasant odor of fruit, recalling that of amyl acetate. It has a density of 0.769 at 0 ° and boils at 125°. Insoluble in water, soluble in alcohol and ether. It is found, accompanied by isobutyl acetate (density 0.892 at 0° boiling point 112-113°), in the rectification tails of alcohols.
Amyl acetate or amyl ester. C2H3O2.C5H11 — Colorless, limpid liquid with a pleasant smell of pear or banana when stretched with alcohol. Normal amyl acetate has a density of 0.892 at 20° and boils at 148°. Isoamyl acetate boils at 139° and has a density of 0.876 to 15°. These two esters are found in fusel oils of eaux-de-vie (notably California grape eau-de-vie, according to Valaer), and poorly rectified industrial spirits.
[Amyl ester is an ester of a higher alcohol and acetic acid. It form in California wines when amyl alcohols creates a zone in the column and acetic acid passes by. In excess, it is considered a flaw and why a continuous column still cannot make spirits as extraordinary as a batch or pot still.
Ethyl butyrate or butyric ester, C4H7O2.C2H5. — Colorless, pineapple-like liquid having a density of 0.879 at 20° and boiling at 120°. Not very soluble in water, soluble in alcohol. It is used in the preparation of pineapple and rum essences. It communicates its characteristic fragrance to rum from Jamaica known as “pineapple rum”.
Ethyl valerianate, C5H9O2.C2H5. — Smelly liquid, reminiscent of mint and russet apple. It has a density of 0.866 at 20° and boils at 135°.
Amyl valerianate, C5H9O2 .C5H11. — Oily liquid, with apple odor, having a density of 0.870 at 0° and boiling at 191°. This ester, which is formed in the catalytic oxidation of amyl alcohol, is used to prepare apple and peach essences.
Ethyl caproate C6H11O2.C5H11. — Oily liquid, limpid, whose smell is reminiscent of ethyl butyrate. Density 0.873 at 20° and boiling point at 167° (under 738 mm).
Ethyl œnanthylate or œnanthyl ester, C7H13O2.C2H5. — Oily, colorless liquid with a pleasant odor of fruit, a burning taste, easily volatilising, insoluble in water, soluble in alcohol and ether. It has a density of 0.872 at 15° and boiling at 187-188° (under 760 mm).
Ethyl caprylate, C8H15O2.C2H5. — Colorless liquid, with a pleasant smell reminiscent of that of pineapple, boiling at 205° and having a density of 0.887 at 0°.
Ethyl Caprate, C10H19O2.C2H5. — Oily liquid, insoluble in water, soluble in alcohol and ether, having a density of 0.862 and boiling at 243-245°.
Isoamyl caprate, C10H19O2.C5H11. — It was found by Rowney in the fusels of corn; by Fischer (1) and Grimm (2) in that of grape eau-de-vie; by Johnson, in that of potato.
(1) Ann. CXVIII, 312, 1861.
(2) Ann. CLVII. 267. 1871.
Ethyl laurate, C12H23O2.C2H5. — Oily liquid, colorless, with a pleasant odor of fruit, insoluble in water, slightly soluble in alcohol. It has a density of 0.867 at 19°, boils at 269° and solidifies at -10°.
Ethyl palmitate, C16H32O2.C2H5. — Solid substance, crystallizing in prisms, melting at 24° and boiling at 184-185° under 10 mm.
According to Lebbin, we would also find, in rums and araks, esters of aromatic acids (phenylacetic acid group). Indeed, after heating the rum in the presence of sodium hydroxide for 1 hour, 1/2 to 1 h. 3/4. Sufficient time to obtain the saponification of esters of fatty acids, the characteristic bouquet of the eau-de-vie has not yet disappeared. The aroma is completely destroyed only after a heating time which varies, depending on the nature of the product, from 2 to 5 hours. The esters decomposed during this second saponification are, according to the author, aromatic esters, which can be saponified only by prolonged heating.
[This either implies another type of ester not based on fatty acids but something else or compounds like rose ketones.]
Finally, occasionally encountered, especially in rums made with molasses from sugar factories treating the juices by sulfitation, ethylsulfhydric esters, substances with foul or alliaceous odor, which give the eau-de-vie an unpleasant odor.
According to E Bauer (3), sulfur is often found in the form of hydrogen sulphide or organic compounds in spirits. Two samples of beet molasses alcohol examined by the author respectively contained 0.00506 and 0.00689 gr. of S per liter. It would be to these bodies that we should attribute the taste and smell of vinasse presented by certain alcohols.
(3) Proc. 7. Int. Cong. Appl. Chem. 1909.
Many authors have reported the presence, in raw alcohols and eaux-de-vie, of basic nitrogenous substances, with an unpleasant smell reminiscent of that of pyridine bases and nicotine. They would intervene to give the eau-de-vie a particular dryness and harm the quality.
[This is probably felt as an acrid chemical dryness.]
Krämer and Pinner (1) were the first to find, among the substances contained in fusel oils, a base which they thought they could identify with a collidine. A few years later, Schrötter (2) isolated in the fusel of beet molasses two liquid bases, having as empirical formulas C8H12N2 and C10H16N2.
(1) Ber. Deut. Chem, Ges. II, 401 1869.
(2) Ber. Deut. Chem. Ges. I, 1431 1879.
Ordonneau (3) recognized the presence of organic bases in various eaux-de-vie (beet, corn, Cognac spirits spirits) and considered them to be formed by amides, pyridine C5H5N and collidine C11H8N.
(3) Bull. Soc. Chim. XLV, 33, 1866.
Morin (4) (1888) was able to isolate, by fractionation of beet molasses fusels, three bases respectively boiling at the following temperatures: 155-160°, 170-172°, 185-190°. The largest in quantity, that boiling between 171 and 172° under the pressure of 754 mm, was in the form of a colorless liquid, oily and very refractory, endowed with a characteristic nauseating odor, recalling that of the pyridine bases having a density of 0.982 (at 12°) and as formula C7H10N2. It is very soluble in water, alcohol and ether and is almost action-free on tournesol paper. According to Brandes and Stöhr, this base would probably be identical to trimethylpyrazine-2.3.5.
(4) C. R. CVI 360, 1888.
Later, Bamberger and Einhorn (5) isolated in pure form a commercial amyl alcohol, dimethylpyrazine-2.5, C6H8N2, and piperazine, C4H10N2; they further recognized the existence of C5H5N pyridine of pyrazine C4H4N2, and methylpyrazine C5H6N2.
(5) Ber. Deut. Chem. Ges XXX 224, 1897.
Chapman and Hatch (6) found as basic constituents of a fusel oil originating from Yugo-Slavia: trimethylpyrazine and tetramethylpyrazine. In addition there were 2 isomers of tetramethylpyrazine, probably constituted by ethylpyrazines, and small amounts of higher homologs, one having the formula C9H14N2. These authors could not detect the presence of pyridine or collidine.
(6) J. Soc. Chem. Ind. (Trans ) XLVII, 97, 1929.
Shorengin, Isagulyants, Belov and Alexandrova (7) found trimethylpyrazine, tetramethylpyrazine, diethylpyrazine and triethylmethylpyrazine in potato fusel oil.
(7) Ber. Deut. Chem. Ges. LXVI – B. 1087, 1933.
With regard to the special case of rums, Greg has consistently found organic bases in the Jamaica rum samples he examined, in more or less important quantities. By stirring the rum with chloroform and evaporating, a residue is obtained in which the perfume of the essential oil is masked by the unpleasant odor of the organic bases.
The author attributes to these a lack of softness and a bitterness, which make some young rums almost undrinkable. Having also been able to detect the presence of organic bases in the cane juice, but only when it is preheated in the presence of excess lime, Greg considers that the lime has the effect of releasing these products combinations in which they are engaged and emphasizes the disadvantages resulting from excessive liming, as regards the aroma of rum.
[Kervegant is referencing Percival Greg who first identified a Pombe yeast in Jamaica in the late 1890’s. Arroyo describes the same phenomenon in his Circular 106. pH is a great help in avoiding anything unpleasant. This also may indicate a Greg document I haven’t found yet.]
The quantity of organic bases in spirits is quite variable: low in the case of eau-de-vie, it is higher for rums and especially for beet molasses phlegms. Lindet found the following figures in gr. by hl. pure alcohol:
[It is hard to say what phlegm means specifically because of other word choices Kervegant has made previously. I’ve been told it best implies stillage.]
To calculate the content of organic bases from the ammonia assayed, the author used the coefficient 100/23 5, the basic sample which he had in his hands and which boiled 179 to 180 °, which gave at the analysis 23.5% of NH3.
Nitrogen found in spirits does not come only from organic bases: a part is also in the state of ammonia. According to Reindel and Unterwegen (1), it is especially in the latter form that nitrogen would be found in the industrial alcohols which they examined, which contained only traces of organic bases.
(1) Z. Shiritusind. LVII. 182, 1934.
The ammonia results mainly from the decomposition, during the distillation, of the ammoniacal salts added to the must and, for a small part, from the degradation of the nitrogenous organic matter by the yeast. Its proportion in industrial alcohols depends mainly on the quantities of ammonium sulphate used: it is rarely greater than 1 mgr. per liter (Reindel and Unterwegen). It would be present in greater or lesser quantity in all phlegms, according to Bauer.
[It is hard to say what phlegm means specifically because of other word choices Kervegant has made previously. I’ve been told it best implies stillage. Here it appears to imply a fraction of the distillate.]
Lastly, it is sometimes added artificially to young eaux-de-vie delivered for consumption, small amounts of ammonia or ammoniacal salts, give them a character of vétusté.
Terpènes, essential oils
According to various authors, each phlegm contains a particular volatile essential oil, which belongs to it in its own and differs in its odor from those of other phlegm. This substance gives the product, even after rectification, a taste of origin and can differentiate it from other spirits. With an unpleasant odor in industrial spirits, from which it is sought to be eliminated as completely as possible, it possesses in the eaux-de-vie a pleasant perfume and contributes powerfully to the constitution of the bouquet.
[It is hard to say what phlegm means specifically because of other word choices Kervegant has made previously. I’ve been told it best implies stillage, but here is another tricky case that seems to imply a fraction of the distillate.]
These characteristic essential oils, which exist only in very small proportions, are still very poorly known. They appear to belong for the most part to the group of carbures camphéniques or terpenes.
Ordonneau (2), in 1886, already pointed out the presence in eau-de-vie of Cognac, of a terpene boiling at 173°, highly oxidizable, giving the product its truly vinous bouquet. Windisch (1893) confirmed the presence of terpene-like odorous substances in grape eau-de-vie. Studying the higher alcohols of rums by means of chloroform, he observed the presence of an unsaponifiable substance related to the terpenes, in the residue remaining after evaporation of the chloroform, and having to a high degree the aroma of rum. He made similar findings in the case of kirschs.
(2) Bull. Soc, chim. XLV, 332, 1886.
[Very likely a rose ketone. Being unsaponifiable would differentiate it from the “Bauer oil” which was described of constituting only acids and esters.]
Greg, in Jamaica (1885), applied himself to studying the essential oil, giving the rum its characteristic perfume, but without being able to specify its true chemical nature. It is, according to the author, an oily liquid, with a relatively high boiling point, not very volatile, soluble in chloroform, alcohol and water. It does not seem to be attacked by alkalis or by dilute sulfuric acid (the concentrated acid dissolves it giving a beautiful pink color). It passes, with the distillation, with the products of tail and one finds it largely in the vinasses. It is also found in cane juice defecated with lime.
[This definitely implies a Greg document I have not found. I also have not yet observed this pink color. The emphasis on tales and vinasse bind these compounds to the fate of fusel oil and means that justifying distillation at as low ABV as possible is desirable.]
Micko (1908), studying the rum of Jamaica by means of the fractional distillation method, recognized the presence in the fifth fraction, but especially in the sixth and sometimes the seventh (1), of an aromatic substance with a very pronounced rum perfume, which he termed “aromatic material typical of Jamaican rum”. This substance is found in 2 or 3 fractions if it is original rum, and in a single fraction, when the rum is cut with neutral alcohol. When the alcoholic degree of the rum is high, it passes later to the fractional distillation.
(1) When the rum is fractioned by means of the Luckow birectifier, the distribution of the essential oil in the different portions is a little different. It meets in maximum quantity in the 5th fraction and communicates to this one a turbid aspect. But it can also be found, if the rum is rich in this constituent, in the 6 ° the 7 ° let even the 8 ° fraction, in the form of supernatant droplets on the surface of the liquid.
[This very much conforms to my experience with the birectifier. I have samples of these drops out for GCMS analysis. However, after reading about “bauer oil” I am wondering if their is a relationship.]
Micko was able to specify the essential properties of this aromatic material. It is a colorless liquid, with a particular odor, fine and aromatic, with a boiling point higher than that of ethyl alcohol. However, it evaporates easily on contact with air at room temperature. But in rum, it is kept in solution by heavier volatile substances. It is more easily detected in diluted alcohol than in high-grade rum; its presence is especially noticeable in Jamaican rum heavily cut with neutral alcohol. It is less soluble in water than in alcohol, from which it can be extracted by means of chloroform or petroleum ether.
[One reason it isn’t so noticeable in original rum is because excessive esters like ethyl-acetate obscure it.]
The substance does not respond to the characteristic reactions of esters, aldehydes or ketones, and therefore does not belong to any of these chemical functions. It presents the general characteristics of essential oils and is probably related to terpenes. Very soluble in the diluted soda, it becomes, by a prolonged contact with this base, more resinous and its smell is modified. Under the action of sulfuric acid, it gives rise to bodies soluble in soda lye.
[If indeed we are talking about rose ketones, I don’t know how to explain the ketone comment. My guess is it is not well isolated but part of an oil that also contains other stuff like the “bauer oil” which is why soda may change its aroma. Rose ketones are described as having radiance and modifying the perception of compounds they are blended with. The soda could have neutralized another component.]
Micko has found the aromatic material typical of Jamaican rum in various other cane molasses eau-de-vie: rums from Cuba, from Demerara, arak from Batavia. However, it exists in a quantity much smaller than in the rum of Jamaica, and its presence is most often masked by esters and other particular aromatic products, with smells of fruit or flower. To demonstrate it by fractional distillation, it is important to saponify the ester’s beforehand. Thus treated, the rum of Cuba, for example, presents in the fourth fraction the aromatic material typical of Jamaican rum; in the fifth fraction an aromatic substance with a leather odor (2), and another with a peach flavor, which can also be detected in the seventh and eighth fractions by chloroform extraction. Demerara rum behaves in a similar way.
[I have yet to try this saponification experiment but it seems like something I should prioritize.]
The essential oil of rum, or essence of rum, studied by Micko, has since been found by many chemists (Kappeler and Schultze, Strunk, Arroyo, etc.), in the rums of the most diverse origins. Arroyo, during his experiences in Puerto Rico, has found its constant production in the fermentation of melasses and cane juice. But the quantity obtained is always minimal and very variable according to the race of yeast, the composition of the must and the mode of fermentation.
(2) Greg had already been able to extract from the petroleum ether some rums from Jamaica with a smell of leather, an aromatic principle whose smell was exactly like that of fresh leather or Russian leather. This principle has been met by many authors (Micko, Haupt, Wüstenfeld and Luckow, etc.) in rums from various sources (but especially in those of Jamaica and Batavia’s araks) and even in “German rum”, obtained from beet molasses (Haupt).
[The smell of leather again points at a rose ketone.]
Pretreatment of the raw material with milk of lime increases the production of the oil during the fermentation, which Greg had already noted previously. Distillation by means of batch apparatus also makes it possible to collect, in the distillate, a greater quantity of this aromatic principle. Finally, Arroyo has observed that the essential oils formed by the various races of yeast may have, from an aromatic point of view, slight differences.
[I have observed these slight differences examining many of the greatest rums on the market.]
Rum essential oil seems to play an important role in the bouquet of rum and, of its more or less high proportion, would indicate mainly the quality of this spirit (Greg, Arroyo, Guillaume).
[Guillaume developed the Galion grand arôme in Martinique and now we see he was very much aware of rum oil.]
In addition to rum oil, Micko has detected the presence in rum of Jamaica of another terpene substance, the smell of which is reminiscent of juniper essence, and which immediately precedes or accompanies in fractional distillation, the typical aromatic material. This terpene, which is insoluble in the soda of lye and loses little or no aroma by prolonged contact with it, however, according to Micko, plays a relatively minor role in the constitution of the bouquet, because its weak smell (1).
(1) However, it would be appropriate to make an exception for certain types of rum, such as the “cœur de chauffe” of Martinique, which has a pronounced fragrance of genievre.
Sikhibusan Dutt found in fusel oil from the distillation of cane molasses in India a crystallized ethylenic hydrocarbon with a boiling point of 62° and a very pleasant odor resembling that of the essence of petitgrain. This body, which has the formula C30H60, seems to be identical to melene.
[Petigrain is a product of citrus treese and melene appears to be a product of bees wax.]
Taira and Matsujima, Japan, also found diterpenes in the fusel oils of cane molasses.
Finally Marvel and Hager found in the “Bauer oil”, an unsaponifiable material, which gave the oil an amber color and an unpleasant smell reminiscent of that of pyridine. This substance, which contained traces of sulfur, but no nitrogen, could not be identified because of its small quantity and the absence of a fixed boiling point; it has been suggested that it may be composed of hydrocarbons of the terpenes group.
[Very likely a rose ketone. Not every likes the smell in isolation.]
Schorigin and Savenkov (2) reported the presence in the Russian fusel oils of an unsaturated hydrocarbon C15H26 (boiling point 80-81° at 5 mm) and 3 saturated isomeric hydrocarbons C15H28 (boiling point 128-130°, 117-118° and 106-107° under 12 mm), which appear to be dicyclic sesquiterpenes.
(2) J. Gen. Chem. Russ. IX, 1437, 1936.
Fixed matter: dry extract and ash.
Industrial alcohols, generally preserved in metal containers, do not contain fixed materials in solution. Beverage alcohol, on the other hand, being most often stored in wooden casks, dissolve a certain quantity of tannic and resinous principles. At the same time, spirits for consumption are often colored with caramel and sweetened with a slight addition of sugar or glycerin. They can also receive sauces, in which fixed materials dominate.
It is interesting to know the amount of dry residue, as well as the nature of the extractive materials, which contribute to the formation of the bouquet and can give valuable information on the origin of the product examined.
Quantin has long pointed out that the examination of the dry extract of rums provides a more precise basis of assessment than the determination of the volatile part alone. More recently, Valaer has recognized that this review is the surest way to pinpoint the provenance of the various rums found in the US market.
Rums of consumption contain a relatively high extract rate. Miss Moroy (1) reports, for example, for rums consumed in France that 2/3 of the samples analyzed at the Laboratory of the Ministry of Agriculture in 1935 had an extract between 4 and 6 gr per liter. Partridge (2), in England, found, for 43 rums of various origins, a rate varying from 3 to 13 gr per liter. Rocques, examining, in 1926, 27 rums of French colonies as they are at the time of their embarkation, that is to say, colored with caramel and having spent a few months in charred oak barrels, found that the extract ranged from 1.44 to 9.0 gr. per liter for products from Martinique and from 2.48 to 16.18 gr. for those of Guadeloupe.
(1) Ann Falsif. XXX 160, 1937.
(2) Analyst XLVII, 772, 1932.
Some types of rums, however, can achieve significantly higher figures. Thus, Valaer found up to 22 gr. extract per liter in rums from Cuba and 30 gr. in those of Demerara. These products are not only colored with caramel, but have also received significant amounts of foreign materials (fruit juices, sauces, etc.).
Rums not colored artificially and only aged in casks have a much lower rate of extract. Valaer, in the United States, found that the dry extract could reach, after 2 years of storage in barrel, 1-2 gr. per liter. Analyzes carried out in the laboratory of the Department of Agriculture of Martinique gave for rums of vesou with no caramel and stored in barrels of charred oak (in gr per liter):
Other brandies have, in general, a dry extract significantly lower than that of rum. While it usually varies for commercial Cognac between 6 and 12 gr. per liter, it rarely exceeds 1 to 2 gr. in kirchs, marc and cider eau-de-vies. The eaux-de-vie of charentes used for the preparation of commercial Cognac marks have an extract rate of between 0.5 and 3 gr.
The main constituents of the solids may be the following substances:
Caramel. — Caramel is constituted, as we have seen, by a mixture of iso-saccharosane and humic substances. The coloring of the rum is usually due, in whole or in part, to the caramel. However, we must except rums made in the United States, and some types of rums from Cuba and French colonies.
[So, U.S. rums, Cuba and some French colonies at the time didn’t color with caramel.]
Tannins. — The tannin in rum comes from barrel wood and, in some cases, the treatment of eau-de-vie with charred oak chips. The tannin content varies greatly depending on the duration of aging and also the condition of the containers (new or used, charred or uncharred). In rums not containing caramel, the coloring is generally due solely to the dissolved tannic principles, which constitute the greater part of the dry extract of rums aged in barrels and not having received foreign ingredients.
An excess of tannin gives the spirits a special unpleasant taste, called woody. Also, in the case of fine eau-de-vie, we avoid using new barrels and prefer to complete the color by means of a caramel addition.
Sugar. — In order to give more mellowness to the eau-de-vie before delivering it for consumption, often a sugar syrup is added. In general, the dose of 0.5% of sugar is not exceeded, except if it is a question of masking a natural defect of the spirit. After some time, the sucrose undergoes inversion, and there is found in the eau-de-vie a mixture of reducing sugars and sucrose. Windisch (3) found in the rum samples that he examined levels of 0 to 0.464% sucrose and 0 to 0.277% of reducing agents.
(3) Arb, Kais. Gesundh. VII, Bd. 2, 1892
Glycerin. — Spirits of consumption sometimes add a little glycerin, to give them softness. Small amounts of this substance can also be found normally in spirits as a result of the fermentation, glycerin being driven by the steam. Ordonneau notably found in cognac, the measure of 4.38 gr. by hl. eau-de-vie.
Fixed acids. — Among the fixed acids used in the composition of the extract, succinic acid, and sometimes lactic acid, products of the alcoholic fermentation, produced in small quantities by the steam during the distillation, may be distinguished; the acidic principles dissolved by the alcohol from the wood of the casks, during aging; the acids brought by the sauces and various ingredients added to the rum in order to improve or modify the bouquet. Among the latter, citric acid, supplied by certain fruit juices (pineapple, oranges, etc.), has been mentioned, and tartaric acid, which meets, according to Quantin, are accompanied by tartrate and sulphate of potash, in some rums colored using black Malaga wine.
[You would think spirits would have more lactic acid, but for some reason it isn’t so prominent.]
Sulfuric acid is sometimes also added to rum to promote formation of esters: Valaer cites the case of a rum from Montevideo (Uruguay), whose fixed acidity, which reached 31.6 gr. (as acetic acid) per hl. eau-de-vie at 52° was due solely to sulfuric acid. The pH of this eau-de-vie went down to 2.8, while for rum it is usually between 4 and 6.
Essential oils. — In some countries, to convey a special bouquet, rum often uses various spices and herbs (coconut, nutmeg, Tonka beans, cloves, vanilla, areca nuts, etc.), containing low-volatile essences and terpenes, which is found in the dry extract.
Mineral matter. — The mineral substances found in spirits come from the distillation apparatus, water used for dilution or storage containers.
The acids of the musts can attack the metal of the distillatory apparatus, and it passes in the eau-de-vie a certain quantity of tin (tin coils), lead (coils welded with an alloy of tin and lead) and especially copper. It is mainly when new appliances are used that the attack is pronounced. The entrained copper then communicates to the eau-de-vie an unpleasant taste and, if it is noticeable, a hazy color. In the long run, a patina is formed which prevents the metal from being attacked further. When the appliances have been idle for some time, there is some verdigris, which goes into the brandy if we have not taken the precaution of carrying out a preliminary cleaning, by distilling a little water before putting the appliances back into service.
The presence of copper and tin salts may also arise from the residence of spirits in previously tinned containers, and that of zinc from the passage in zinc containers or galvanized sheet.
According to Hayes (1), spirits, all of which contain, with some exceptions, Cu, Pb and Sn salts when they have just been manufactured, would be stripped of these during aging in barrels: the extracted organic matter from the wood would be combined with the metallic salts, which would be precipitated and found as a deposit of brown matter, at the bottom of the barrel.
(1) Chem. News IV, 117, 1861.
When liquids loaded with mineral salts are used for the dilution of spirits, the ash content may be substantially increased. Calcium from calcareous waters is found in the extract in the form of lime acetate.
But, in general, it is especially during the conservation of spirits in barrels (particularly when heat treatment is applied), and then in bottles, that the rate of mineral matter increases, by the dissolution of wood and glass minerals (soda, potash, lime, iron).
Windisch found, for rums of various origins, ash levels of 1 to 20 gr. per hl. In the case of rums kept in bottles for periods ranging from 1 to 22 years, Strunk measured 4.8 to 35.6 gr. of mineral matter per hl. of eau-de-vie. Valaer reported the case of a rum from Uruguay. which contained up to 140 gr. of ash (sulphate of soda) per hl.
[Uraguay, get your shit together!]