Kervegant Chapter X Purification and Artificial Aging

Purification and Artificial Aging Chapter X:

Pages: 280-297


The slow pace of natural aging makes it necessary to maintain considerable stocks, the wear and tear of which, in addition to the interest on immobilized capital each year, weighs heavily on the cost of spirits. So we have always sought to accelerate natural aging.

As for the special case of rums, Charpentier de Cossigny already indicated, at the end of the XIX century, a certain number of processes.

“The lime in nature, mixed with the guildive or the taffia,” he wrote, “diminishes the nauseating odor of this liquor, but does not destroy it entirely. The addition of the vitriol oil seemed to me to have more effect, but it is to be feared that it will attack the vessels; the addition of sea salt succeeds even better. It is appropriate to use these last two interludes only during the rectification; and I would not add lime either alive or extinguished, except with the product of the first distillation. We would decant the brandy after the precipitation of the lime ….”

[The lime would be for salting out acetic acid. Vitriol oil was an early name for sulfuric acid and may have simply been used to convert acetic acid to ethyl acetate.]

“There is another way to weaken the nauseating smell of these eaux-de-vie: it is to expose them uncovered in the sun for one or two days at most, according as it is more or less hot. The most volatile part evaporates, it is the rector spirit; and the eau-de-vie loses very little of its strength. It has been pretended that the fine liquors, newly prepared, acquire the quality of the old by putting the vases which contain them in ice for a few hours. I tried this way without success; but I felt that fire produced this effect. I put bottles of fresh liqueurs in a pail filled with water on the fire; after a few hours of boiling, they had acquired the qualities which antiquity gives them, that is to say that all the substances which compose them have combined more intimately than they were; from which it follows that they have a more agreeable and mellow taste.”

[Evaporating spirit in the sun may reduce excessive acetaldehyde if its present. Heating them in a double boiler may temporarily create esters beyond the equilibrium reducing mainly acetic acid in faulty spirits.]

Ducourjoly gives the following procedure, “to give to the new rum, in the space of a month, the color and the taste of the oldest rum”:

“For 300 gallons of rum, take: 1° : 4 baker’s loaves, one pound each; they are opened to remove the crumb, the crusts are roasted until they are almost reduced to charcoal; they are allowed to cool well and crushed.”

“2ï : 4 pounds of raisins, drawn, if possible, from Malaga, if there is a lack of grapes, take dried prunes that are crushed with the stones and pulp together.”

“3° : 1 book of green tea.”

“4° : A dozen ripe pineapples of good quality, crushed without removing the skin.”

“We put, in 300 gallons of rum, all these ingredients, divided according to the size of the casks that contain it.These casks must not be exactly filled, so that by rolling and shaking them strongly, we can brew the liquor: what you have to do exactly at least once in 24 hours, for 15 days.”

“They are not exactly clogged so that the excessively effervescent parts can evaporate, then they are poured out, and this liquor is allowed to stand for another 15 days; after this time, we can give it to drink as old.”

Wray advises treating rum freshly distilled with carbon and lime. “The method I have used myself,” he writes, “and of which I know many others have found themselves equally well, is to have a wooden case about two feet in diameter, having in the center a partition that reigns up to an inch from the bottom. It is filled with coarse powdered carbon, through which the rum passes as it leaves the condenser; the carbon absorbs a considerable portion of the oil, and the rum leaves the filter substantially purified. It then enters the rum vat, containing about 300 to 500 gallons, placed at a sufficient elevation. There the rum is treated with quicklime; it is strongly agitated so that the lime is well distributed throughout the liquid. After two days, we taste the rum; if it is good, the contents of the vat is passed to the carbon filter, as the first time, then it is transferred to another vat to take color. If we recognize that we did not use enough lime, we put a little more by mixing everything together, and the rum is tasted again after two days. The lime is then at the bottom of the vat, where it is deposited after having formed with the essential oil an insoluble salt.

[Essential oil here may simply be fusel oil. This use of lime in the distillate may have been necessary if they were suing a proto-version of the vinegar process to reduce excessive acetic acid.]

“By this carefully practiced process, I saw selling one-month-old rums for two or three-year-old rums, as the flavor of the rum had improved. It is, however, very important to point out that to subject rum to this operation requires as much care as reflection. Too much lime would make it a neutral spirit, totally devoid of the well-known taste that belongs to rum. But if the distiller gives only the slightest degree of attention to his task, it is impossible for him to be go wrong.”

It is especially in modern times, where the demands of trade, competition, often insufficient capital, force producers and traders to sell their products as quickly as possible, that the rapid aging methods have taken importance. Much, if not most, rums sold in some markets, particularly in the United States, have been artificially matured.

The methods used are numerous and varied. They aim sometimes to accelerate only the work of time, by acting on aging factors (temperature, oxidation, etc.), sometimes to eliminate substances that give an unpleasant taste to young eaux-de-vie (hydrogenation), sometimes finally to modify the bouquet of spirits and to communicate to them a character of vétusté by addition of foreign ingredients.

[vétusté may be a word we should adopt.]

Although the products obtained do not reach the quality of natural aged eaux-de-vie, they are superior to newly distilled spirits whose defects are suppressed or masked. Natural aging and artificial aging are often associated, so as to reduce the duration of storage in barrels.

Carbon treatment

Filtration on charcoal.

Filtration on charcoal has been widely used in the past for the purification of tasteful industrial alcohols.

The carbon, in the form of a mixture of dust and nut-sized fragments, is placed in vertical cylinders of sheet metal, 80 centimeters to 1 meter in diameter and 4 to 6 meters in height, joined together as a battery of 5 to 10 elements. The alcohol, diluted beforehand at 40-50°, runs successively through the various cylinders, the first of which contained the oldest carbon and the last of the newest carbon. When the first filter is saturated, it is recharged with fresh coal and passed to the battery tail.

The spent carbon was first stripped of the retained alcohol by distillation in a stream of water vapor, then revived by heating to dark red in open sheet retorts or by treatment in a vacuum with superheated steam. Preference was given to very light (apparent density 0.15), willow or poplar carbons. These were prepared, not by calcination in millstones, but by heating in closed vessels, similar to those used to prepare pyroligneous acid.

Carbon filtration, quite expensive (loss of 2 to 2.5% of alcohol and consumption of about 5 kilograms of coal per hl of filtrate at 40°), has been abandoned in the alcohol industry, since powerful corrector columns are available, allowing a perfect separation of the impurities which pollute the ethyl alcohol. But it has been maintained in the preparation of various beverage alcohols, including certain types of whiskey and rum.

Tennessee whiskey, for example, manufactured in the United States, is filtered, on charcoal leaving the still. It is prepared on a brick surface, in the open air and preferably with maple wood, pushing the carbonization so as to eliminate all volatile matter. It is then divided into pieces the size of a grain of corn and placed (by squeezing the layers) in frustoconical filters, measuring about 2.70 m. high on 1.80 m. diameter at the top and 1.50 m. at the base. Usually, there are 6-7 filters side by side. The first alcohol that passes is returned to the distillation column. When the alkaline carbonates contained in the coal have been well washed, or after passing about 12 barrels of alcohol per filter, the flowing liquid is sent to the whiskey tank, to be barreled and aged in the usual way. The coal is renewed as soon as the distiller finds that the filtrate no longer has its characteristic pleasant odor. A filter of the dimensions indicated above, containing 80 bushels (2,900 liters) of coal, can treat about 80 barrels (17,000 l.) of whiskey, and a battery of 7 filters to pass, given the time required for operations of emptying and loading, about 3,600 liters of liquid per day. The loss in filtration is 12 to 15% (Dudley) (1).

(1) J Amer. Chem. Soc. XXX, 1784, 1908.

[That loss seems quite large and is not doubt much lower these days.]

In Cuba, rum is usually passed through on charcoal filters leaving the distillatory apparatus. It is the same sometimes in English Guiana, where the guava charcoal is particularly appreciated for this purpose. On the other hand, this operation is never practiced in the French colonies.

The coal exerts on the spirits an action at the same time mechanical (absorption of certain impurities) and chemical (oxidation). The experiments of Glasenapp (2) have shown that the latter is predominant. A small portion of the ethyl alcohol and higher alcohols is first transformed, by the oxygen of the air contained in the charcoal, into aldehydes; then these in fatty acids. The acids form esters with alcohol, which explains the improved taste and aroma of the filtered alcohol.

(2) Z. Angew Chem. 1898, 617, 665.

The absorption takes place mainly with respect to aldehydes, acids and esters, but as new quantities of these substances are formed during the operation, their level in the filtered alcohol may be increasing or decreasing according to whether the raw spirit contains weak or strong proportions. Higher alcohols, contrary to what was believed for a long time, are poorly retained by the coal. However, there may be some reduction in the level of the latter in the filtered alcohol (oxidation), or on the contrary an increase, which comes either from a saponification of the esters or the formation of substances soluble in carbon disulfide (3).

(3) Glasenapp in his experiments used the Röse method for the determination of higher alcohols.

The nature of the physicochemical phenomena that occur during filtration seems to depend on many factors: composition of raw spirits, duration of filtration, temperature, state of exhaustion of carbon, etc… The absorbing action of the latter appears in particular to decrease more quickly than its oxidizing action, as shown by the figures below obtained by Glasenapp, by analyzing the alcohols supplied at the various stages of filtration, at the Balk factory in Riga.

According to Dudley, the charcoal-filtered whiskey has a flavor and smell quite different from that of the unfiltered product. The original tastes (depending on whether alcohol was obtained from rye, corn, etc.) disappear, and the bouquet becomes uniform, while it is refined and softened. The trouble that appears when you dilute the raw whiskey with water, no longer occurs after filtration. It seems, therefore, that there is the elimination of essential oils from the kernels. Furfurol disappears completely. The author gives, among others, the following analysis of a “Tennessee whiskey”, before and after filtration:

According to Krzyzanowski (1), charcoal filtration would greatly improve the flavor of young spirits, which would become milder, but would have little effect on the smell of the product.

(1) Przemysl. Chem. XXII, 171, 1938.

Carbon, instead of being used for filtration, can also be used in the form of a fine powder, which is mixed with alcohol, after having previously diluted it with a little brandy. It is left in contact for one or two days, stirring from time to time, and after deposition, is separated by decantation. Ordinarily, 500 grammes of carbon per hectolitre of brandy are added. This process, which was once widely used for the purification of industrial alcohols, was later replaced by that of filtration, which was easier. Today, it is usually reserved for the treatment of bad tasting eaux-de-vie.

Various carbons.

For the purification of spirits, activated charcoal, animal black, etc., which have a higher absorbency than charcoal have also been advocated. It is important that the products used be very pure, especially bone charcoal, which often contains empyreumatic substances that impart bad tastes to alcohol.

Zaharia, Angelescu and Motoc (2) studied the absorbing action of Merk’s animal black, under oxidation-inhibiting conditions: the duration of contact was reduced to 10 minutes, a time sufficient to reach the absorption equilibrium. They found that the absorption was higher when the alcohol content was lower and the molecular weight of the impurities higher.

(2) Chim, et Ind. XXXI, N° special, 989, 1934, Bul. Soc. Chim. Romania XVI, 61, 1935.

Here are the absorption rates observed for various impurities in eaux-de-vie:

The treatment applied to a plum brandy from Romania not only reduced the level of known impurities, but also significantly improved the aroma and bouquet, although there was no oxidative action or estérifiante. This improvement results from the elimination of certain unknown substances, which adversely affect the flavor and smell of eaux-de-vie.

Comparing the action of various carbons: Charcoal, Blood, Norit Active and Pickes Active, the same authors observed that the absorbency with respect to higher alcohols, zero for charcoal, increased in order : Charcoal, Norit, Pickes. On the other hand, the absorption capacity with respect to acides, aldehydes and esters was high in the case of charcoal and Norit, and low in the two others. Absorption is proportional to the concentration of impurities except for acetic acid.

J. Caffre (1) used activated charcoal at the rate of 500 grammes per hectolitre to treat a bad tasting brandy, on which the usual absorbents had produced no result. He found that not only did the bad tastes disappear, but the tastes of terroir too pronounced and unpleasant were diminishing. The level of impurities decreases and their composition changed. A commercial eau-de-vie thus treated gave the following results to the analysis:

(1) Viti viniculture, juil. 1927, 241.

[Keep in mind, this is the older usage of terroir and likely akin to Tufo.]

The dry extract disappears and the eau-de-vie loses a large part of its organoleptic qualities.

Mr. E. Barker patented in 1936 the following process. The freshly distilled brandy is stirred in a closed container with activated charcoal (2 – 5 kgs / hl) at a temperature of 90°. Small amounts of air are introduced during the operation, to allow the transformation of aldehydes into acids. Then, the alcohol is treated with the same quantity of activated charcoal, but at a temperature of 40-50 ° and in the absence of air, so as to esterify the acids. Finally to develop the coloring and flavor, the liquid is heated in the presence of coal obtained by distilling wood at 250-275°. [Quite fascinating. The very last part with the high temps is the destructive distillation of wood to produce charcoal.]

Treatment with oak chips.

One of the most frequently used methods to accelerate aging is to treat the eaux-de-vie, by maceration or filtration, with oak chips, fresh or charred. The solids and acids, as well as the coloring, are increased, but the esters and the higher alcohols are little or not modified. If the treatment is too thorough, the brandy has a woody taste.

Haüssler (1) studied the variations in the composition of a cognac kept in bottles and in which maceration of oak shavings had been carried out at a rate of 400 grammes per 3 liters of eau-de-vie. He observed, after a few months, a decrease of the alcoholic richness of 1-2%, due without doubt to an oxidation and an absorption of the alcohol by the chips. The solids content increased to 0.1-2.0 grams per liter after two months, and to 7.5 grams after 15 months. Fixed acids and volatile acids increased steadily over time. The ashes also underwent a slight increase; however, their rate remained stationary after some time. The higher alcohols and esters fluctuated, but of small amplitude, especially the higher alcohols, which increased or decreased as the case may be.

(1) Z. Offentl. Chem. XX, 184, 1914.

Here, according to P. Valaer, the composition of two molasses rum from Pennsylvania, the first untreated, the second having been filtered for about 5 hours and at a temperature of 26° C, on oak chips grilled, at a rate of 634 kilograms of chips per batch of 36,000 liters of 50° eau-de-vie:

According to Valaer, uncharred chips yield more dry extract and acids than the charred or toasted chips, but less ash and coloring matter.

In the United States, whiskeys and rums, especially light rums delivered for consumption immediately or after short-term storage, are frequently processed with chips. These, usually toasted or lightly charred, are placed in filters, through which the spirit is passed several times, for a variable time (usually 5 or 6 hours).

Wine spirits are not subjected to the above treatment, which gives them too pronounced a woody taste. Sometimes a certain amount of freshly toasted chips are introduced into the barrels. It is considered that this addition gives good results, when the spirits should not be kept for more than four years. A dose of 4.5 kgs of chips per hectolitre of spirits is sufficient (Joslyn and Amerine) (2).

(2) California Agr. Exp. Sta. Bul. 652, 1941.

In France, aging with chips, applied quite often to common eaux-de-vie, is practiced by mixing the newly distilled spirits with alcoholic waters, in which unburned white oak chips were macerated. These are first soaked for a week or so. After removing the first water, which must never be used, the shavings are covered with rainwater or very pure water, mix with alcohol to 20 or 25 degrees. The proportion is 10 kgs of chips per hectolitre of water. Sometimes you add a little sugar cane molasses (2-3 liters per hectolitre) or grape syrup (1-2 liters per hectolitre). Barrels containing alcoholic water are plugged lightly and kept in a room at high temperature, for a year or two generally, but never less than six months. At the end of this time, the small waters have taken on color and acquired a special taste called “rancio” an evident flavor and a balsamic smell. They are used to reduce the new brandies grading 67-70 ° and reduce their measure to 50°.

Krebs and Mather (1935) proposed, to facilitate the dissolution of the principles of wood, to prepare the oak chips in the following manner. After roasting until light brown in color, the chips are washed, at a temperature of 30-40° C, with a solution of magnesia chloride (at 0.5%) or chloride of lime (at 0.05%), and then put into contact with an emulsin solution for a while. After maceration in 0.25% diluted acetic acid, the chips are mixed with corn flour, and the whole is kept wet for two to four days. The product is then drained and macerated in the eau-de-vie to age, twice (1 + 24 hours). This treatment would activate the development of mushroom spores contained in oak wood, which would provide various products (amino-succinamide, etc.) helping to give body to spirits. At the same time, aromatic substances with a smell of flowers and fruit are formed, while the tannins are dissociated, aldehidification and esterification of the alcohol are facilitated.

Malzevin advocated the replacement of chips with oak wood extracts, which makes it easier to measure the amount of extractives to add to eaux-de-vie. [I think this is what is practiced today and referred to as bois.]

Coffre proposed to previously treat the oak chips, placed in wicker baskets, with ozonized air. [ozone].

Aging by temperature

The phenomena of oxidation and esterification are accelerated by a rise in temperature, whose action on the aging of eaux-de-vie and wines has been known for a long time.

There are several ways to apply heat to spirits: heating brandy in a vacuum, pasteurizing, heating storage rooms, etc.

As we have already mentioned, the heating of the storage houses is commonly practiced in the United States. The temperature is generally maintained around 20 – 25° during the cold months of the year, using steam coils. According to Brown, a uniform temperature of 20 – 26° would be very favorable to the maturation of spirits. This explains why in tropical countries, where the thermometer usually oscillates between 25 and 30°, aging is particularly rapid.

The tranchage consists in slowly bringing (1° per minute) eau-de-vie to the temperature of 60 – 80°, in a closed container, and then let cool slowly. This operation is generally carried out in a tranchage bowl consisting essentially of a cylindrical copper tank, tinned inside, provided at its upper part with a lid sealing closed and provided with a safety valve. Inside the container is a tin-plated copper steam coil, and on the side a thermometer which gives the temperature reached by the liquid, as well as a sight glass. Tranchage is mainly used to give uniformity and softness to spirits that have just been mixed or added with foreign products.

[This is very much like sous-vide.]

Frequently, heat is associated with other treatments: wood charcoal, oxidation by air or pure oxygen, etc. Pinasseau (1910), for example, has the alcohol arrive in a column divided into two compartments by a perforated false-bottom. The upper compartment is filled with oak chips, and the alcohol, passing on them, is partially evaporated by a hot air current which circulates in the opposite direction. The mixture of alcohol vapors and water vapors goes, leaving the column, in a coil surrounded by a cooling mixture: the alcohol is collected in a container placed under the coil, while the water and the others substances are frozen and remain adherent to the walls of the coil.

[I don’t completely understand what is happening here.]

In a recent patent by Caywood (1935), the liquid is placed in a closed vessel in contact with carbon and is agitated in the presence of air. At the same time, the temperature is raised from about 43° to a point slightly below the boiling point of the alcohol, for about ten hours, in order to remove low-boiling impurities. The temperature is then maintained at 35-38° for about 30 days. The vapors produced during the heating are evacuated.

Barbet gave the name of pasteurized alcohol to the product obtained by returning the alcohol, collected in the condenser, to the upper part of the distillation column, where it is subjected to a strong boiling and from which it is then directed to the refrigerant. The alcohol can also be collected at the top of the column by a special tap; it then falls into a copper box, where it is subjected to a bubbling of vapors taken from the boiler of the still. According to Pacottet and Guittonneau, this operation, which purifies the eau-de-vie without, however, removing its original bouquet, ensures a very appreciable aging, probably due to the sudden evaporation of volatile principles that would have taken several years to escape through the staves of the conservation barrels.

It has also been recommended to pasteurize fermented liquids before distillation, in the presence of carbon dioxide, which, according to some authors, would play a very important role in the genesis of esters and perfumes. This would result in remarkable esterification and an appreciable aging of the eau-de-vie (Barbet, Malvezin).

Barbet (1) advised to operate as follows. Following the fermentation tanks, there are several closed tanks whose total capacity is half a day’s work. Each of these is preceded by a tubular calorizer, or better, a coil fed by exhaust steam or expanded steam, whose intake is adjusted to achieve the most advantageous temperatures recognized. The wine is pumped from the fermentation tank and discharged through the first heat pump into the first closed tank (where the temperature can reach at least 50° C). It requires a continuous and regular passage of the liquid in the calorizers, to ensure the regularity of the chosen temperatures. After the last heating, a copper autoclave is installed, stamped at 1 kg and equipped with a safety valve; its capacity is, for example, the same as that of the boiler of the still. The fermentation gas is captured and discharged into a bubbler located at the bottom of the autoclave. The cooked wine is saturated with pressurized carbon dioxide, the excess of which exits through the valve, and passes into a tubular cooler powerful enough to condense the vapors of alcohol and esters. The condensed liquid is sent to the eprouvette.

(1) C. R. 4. Cong. Int Chim Appl. II, 253, 1900.

[When he says “stamped at 1 kg, what that likely means is that the vessel is a big pressure cooker and it take a 1 kg weight which corresponds to a given amount of pressure. I don’t think it works like a typical cooker where pressure dictates temperature and pushes boiling past 100°c. This is more like time under heat at elevated pressure and possibly a drop in pH because of the CO2.]

In the French West Indies, the distillation columns are equipped with a double wine heater with a high capacity (4-6 meters square of heating surface each for a production of 100 liters of rum per hour), which makes it possible to realize at a certain point the preheating of musts before distillation.

Ricciardelli (2) has achieved a marked improvement in the quality of young wine spirits by exposing them, placed in semi-full bottles hermetically closed, in full sun. There is a decrease in the content of ethyl alcohol and higher alcohols, an increase in acids, esters, aldehydes and clarification of the liquid.

(2) Staz, Exp. Agr. Ital. XLLI, 880, 1909.

Finally, Raoul Pictet proposed freezing as a method of aging. Analyzing the deposits that occur naturally in barrels of cognac kept for twenty years in the cellars of the Charentes, the author found that they were identical to those which are formed in the young eaux-de-vie of the same origin, after freezing up to -120 and -130°. It would result from the appreciation of various experts that, from the point of view of aging, the action of freezing would amount to a stay of 12 to 15 years in barrels (de Lapparent). This process, which is expensive and difficult to perform, has not been put into practice. However, some houses of Cognac lower the temperature down to -10° for about seven days, to hasten the stabilization of eaux-de-vie.

Hydrogenation of spirits

Hydrogenation has been advocated to eliminate substances giving young eaux-de-vie an unpleasant taste and odor (greenness). In the course of natural aging, the latter often disappear much more slowly than the actual maturation process (oxidation, esterification and polymerization phenomena), which gives the eaux-de-vie body and softness. Some whiskeys, for example, are not yet completely stripped of their greenness, even after four years of storage (Hochwalt and Thomas). As the levels of dry extract, acids and esters increase especially during the first stages of storage in the barrel, it would be possible consequently, by eliminating the bodies which unpleasantly affect the bouquet of the young spirits, to reduce the duration of aging considerably.

It has been proposed to use for this purpose either nascent hydrogen (Naudin) or hydrogen in the presence of a Hochwalt and Thomas catalyst.

Naudin process.

Towards the end of the last century, L. Naudin (1) employed the hydrogen supplied by the electrolysis of water by means of a stack of zinc-copper elements in order to purify industrial spirits. The hydrogen produced is absorbed by the alcohol and the oxygen is fixed on the zinc (formation of insoluble zinc oxide hydrate).

(1) Mon. Se. Quesneville (3), XII, 238, 1882; XIII, 862, 1883

The apparatus devised by the author consists of a closed tank made of wood or sheet metal, in which are placed zinc plates, some flat, the other corrugated, alternately. These blades are pierced with holes, to allow the circulation of the liquid. We cover them with copper, filling the tank several times with copper sulphate: the copper precipitates in the powdery state and the apparatus is ready for operation. The alcohol arrives at the top of the tank and is taken up at the bottom by a pump, to be sent again to the upper part: it is evacuated by a special pipe when the hydrogenation is sufficient.

A 105-plate battery can handle 150 kilograms of alcohol at a time and represents a 1,800 square meter hydrogen-producing surface. Below 5° C, the battery no longer operates and, above 35° the reaction becomes tumultuous, which destroys the adhesion of copper on the zinc Between these temperature limits, the duration of the alcohol stay in the device varies from 6 to 48 hours, depending on the composition of the alcohol, the temperature and the condition of the battery. It can work for a year and a half to two years, provided that every 8 days a few thousandths of HCl are added to the alcohol to dissolve the zinc oxide hydrate that forms during electrolysis.

The Naudin process was used industrially, with favorable results, for the purification of industrial alcohols, which were then subjected to rectification. It does not seem to have been applied to the treatment of beverage alcohols.

Hochwalt and Thomas process.

Hochwalt and Thomas advocated in 1934, the use of hydrogen in the absence of air and in the presence of a catalyst (platinum black or nickel powder). The eau-de-vie can be treated either in the vapor state, at the outlet of the distillation apparatus, or in the liquid state.

In the first case the alcohol vapors penetrate, at the temperature of 80-90 ° C, in a special apparatus that they travel from bottom to top. This one receives at the same time as the hydrogen and, at its upper part, water containing nickel in suspension. It only takes 3 pounds of nickel to process 1,500 gallons of spirits. It is also possible to distribute the nickel on pumice stone or any other divider (asbestos, etc.). In this case, it is possible to heat the alcoholic vapors to 100-140 °, which determines a certain esterification.

[Kervegant’s subversive strategy is to terrify you away from artificial aging.]

For the treatment of alcohol in the liquid phase, it is preferable to use platinum black, which is less soluble than nickel, which gives the eaux-de-vie an unpleasant taste and therefore needs to be carefully removed. The catalyst is suspended in the liquid and stirred vigorously as a stream of hydrogen arrives from the bottom of the vessel. The duration of the hydrogenation depends on the quantity and quality of the catalyst employed. In general, with a dose of platinum black of 1 gram for 3 liters of spirits, the operation is completed after about 30 minutes. But it is important to take frequent samples, to be aware of the disappearance of bad tastes and to follow the course of purification. Hydrogenation is slower in the presence of nickel than platinum, and it is advantageous, with the first catalyst to operate at a pressure above atmospheric pressure. When the operation is complete, the catalyst is separated by filtration. Platinum black can be used for 14 successive treatments, after which it is important to revitalize it.

According to Hochwalt, Thomas and Dybdal (1), the catalytic hydrogenation does not alter the content of the spirits in impurities, and does not hasten the maturation proper during the subsequent storage in barrels. Differences can not be detected either by the methods of the physical analysis (pH, refractive index) or by the chemical methods (bromine index, etc.) between the treated alcohols and the untreated alcohols. Only the organoleptic properties are modified: the taste of acrolein, the smells of yeast, vinasse, etc and, in general, the smells and flavors that constitute the greenness of young eaux-de-vie, disappear. The reaction would be analogous to that which occurs in the hydrogenation of oils and fats. It is possible that aldehydes, acids and unsaturated esters are converted into corresponding saturated products, which have a less irritating and less objectionable flavor and odor. If the hydrogenation is too thorough, the eau-de-vie takes on a “peppery” flavor.

(1) Ind. Eng. Chem. XXVII, 1404, 1935.

[When Kervegant says “organoleptic properties”, he is referring to compounds that simply cannot easily be measured by titration.]

Oxidation treatment

Every effort has been made to obtain an acceleration of the oxidation phenomena, which seem to play a predominant role during aging. The patents taken for this purpose for half a century are particularly numerous. They use the action of air, pure oxygen, ozone or various chemical oxidants: oxygenated water, permanganate, etc.


The simplest method for carrying out the oxidation is to increase the contact surface between the air and the eau-de-vie, by a vigorous stirring thereof.

It is possible, for example, to install in the conservation casks finned stirrers, actuated by contraptions or motors. In France, for the same purpose the tuns used for cutting or reducing spirits are sometimes used. To achieve a more vigorous oxidation, it is also possible to inject air under pressure into the liquid by means of a tube with a narrow-opening. The operation is repeated several times a day. This arrangement is very common in some houses of Cognac, where it gives good results (Pacottet).

According to Krzyzanowski, the aeration would bring about a rather important improvement of the odor, but insignificant of the taste. The rate of aldehydes would be significantly reduced.

Pure Oxygen.

Pure oxygen has a much more energetic action than oxygen in the air, which dissolves in liquids in a smaller quantity, because of its tension is five times smaller. [We see this effect in the so-called reflux de-aeration where CO2 is used to force Oxygen out of solution.]

In the apparatus invented by William Saint-Martin and built by the Maison Deroy, the eau-de-vie is pumped by a compression pump into a sprayer formed of two hollow branches, each terminated by a small-diameter nozzle, located opposite each other’s moon. The horizontal liquid threads collide with each other, producing a kind of disc radiating from the center of the nozzles at the periphery of the mixer. A state of molecular division of the almost absolute liquid and an intimate contact with the oxygen under pressure are thus achieved. The sprayer is placed in a mixer, consisting of a copper cylinder greater in diameter than in depth, closed on one side by a hemispherical bottom and on the other by a thick glass, to follow the operation. The products of this fall into a copper container, carrying a water level, a drain pad and a valve for the evacuation of ethereal vapors, which can be expelled or collected.

Villon (1) advised the combined action of oxygen under pressure and heat. In a hermetically sealed copper tank, able to withstand a pressure of 10 Kgs per cm² and jacketed, 200 liters of brandy are introduced through a manhole. The temperature is raised to 50° by opening the valve of the steam pipe and, by a tube, oxygen is delivered at 3 kg of pressure, as it leaves the oxygen cylinders. It is left in this state for 5 hours. Then, the gas valve is closed and the temperature is raised to 75°. The next day, the operation is repeated, and so on 3 or 4 times, so as to gradually reach the desired degree of aging. The oxygen expenditure is 125 to 140 liters per hl of brandy.

(1) Bull. Soc. Chim, (3), IX, 640, 1893.

Malvezin imagined a device based on the same principle. It consists of a large tin-plated tank, with a capacity of 1,400 liters of capacity, very resistant to pressure, which is filled with three-quarters of eau-de-vie. A rotating propeller in a sleeve constantly raises the liquid, which is projected by a second propeller rotating flush with water, in the empty part of the container, saturated with oxygen. Oxygen, supplied by a bottle, enters the upper part of the liquid through a crown pierced with very fine holes. The mass of the liquid is heated to about 60° by a thermosiphon, which sends hot water into an ascending coil placed inside the container.

Wilkie performs the oxidation by bringing the alcohol in vapor state into intimate contact with pure oxygen (or air) under pressure, in the presence of a chemically inert divisor, such as porous carbon. A few seconds are usually sufficient to ensure the transformation of unwanted impurities (acrolein, etc.). The alcoholic vapors are then condensed. The apparatus may be placed between the distillation column and the condenser, and the condensation may be carried out in the presence of oak chips charred or not, so as to give body to the eau-de-vie.

[This is very likely Herman Willkie of Hiram Walker fame.]


Ozone, whose oxidizing power is much greater than that of oxygen, has often been advocated to produce rapid aging of eaux-de-vie. It was Pasteur who for the first time pointed out the property possessed by this gas to purify industrial spirits.

The original method devised by Broyer and Petit and applied by Dr. Teillard, in Tournus (France), was to pass oxygen, electrified by means of Houzeau tubes, in wooden vats containing 500 liters of eau-de-vie.

Villon (2) perfected the process by the use of an electric ozonizer and a bulge column, traversed by a vertical axis equipped with trays and animated by a rapid movement. The eau-de-vie penetrates through the upper part of the apparatus and is thrown by centrifugal force against the walls of the column, in the form of very fine droplets, uniformly undergoing the action of the ozonized air, which flows from bottom to top. The liquid, after having descended the various trays, leaves by the base of the column.

(2) Dictionnaire de chimie industrielle. Paris 1902.

In the Eiseman process, the product to be purified is brought into a closed container, where it is heated to a temperature near the boiling point of the alcohol. The ozonized air is fed by a pipe pierced with holes. It goes, after acting, in a condenser, where a portion of the vapors condense and retrograde in the tank, while the uncondensed products go to a condenser, where they flow to the eprouvette.

Numerous models of ozone generating equipment are presently commercially available (Douzal, Siemens and Halske ozonators, etc.). For the treatment of eaux-de-vie, emulso-dividing tubes are often used. These, founded as injectors Giffard on the principle of horns, are constituted by two tubes terminated one and the other by a conical nozzle and arranged at right angles in a tubular envelope. Ozone, sent under pressure in the first tube, creates by its current a suction in the second, which plunges into alcohol. There is an ascent of the liquid, the liquid coming into contact with the gaseous current, is divided into very fine droplets which emulsify with the ozone. The increase of the contact surface thus produced determines a much greater oxidation.

Opinions are quite divided regarding the value of ozone treatment, Wildemann (1) reports having obtained excellent results with whiskey. “In December, 1869,” he writes, “I went to Boston to set up a factory where I began to use ozone, to remove from whiskey, made with either barley or corn, its empyreumatic taste. The results were surprising: the volatile oil disappeared after a simple contact with ozone and, after 20 minutes, it was, according to experts, equal to 10-year-old whiskey. ”

(1) C.R. LXXV. 538; 1872.

Villon claims to have been able to transform the eau-de-vie from the Charentes into a 20-year-old cognac, with an ozone treatment combined with the addition of small waters aged in the presence of chips. He used the following procedure:

1 °) First oxidation of the eau-de-vie at 67°, absorbing 50 gr. ozonized oxygen per 100 liters;
2 °) Rest for 3 days;
3 °) Reduction at 50° with small waters artificially aged by oxygen under pressure;
4 °) Rest for 3 days;
5 °) Second oxidation, at the rate of 50 gr. oxygen per 100 liters;
6 °) Rest of one month in cask;
7 °) Third oxidation;
8 °) Rest for one month;
9 °) Fourth oxidation;
10 °) Rest for 3 months in cask.

Pacottet and Guittonneau consider that the treatment of eaux-de-vie by the ozone of electrical origin is prescribed for a certain reason. “They perform it,” they write, “treating young eaux-de-vie, not to obtain products equivalent to those aged between 20 and 50, but to destroy the bad tastes, always exaggerated at the origin, and that are due to the boiler, the essential oils or other impurities of the alcohol, and to age them of 5 or 6 years.”

On the other hand, Malvezin affirms that it has not been able to arrive at an appreciable aging by the ozone, without giving a very unpleasant taste to the eau-de-vie; Cognacs thus treated still retained this taste after two years.

More recently. Diemair (2) claimed that ozonation did not improve the quality of the eau-de-vie. On the contrary, it communicates with spirits, even if it is very sparing, a bittersweet and irritating taste. This difference can be corrected by the addition of MgO (0.5 to 1 gr per liter), the eau-de-vie still lacking finesse and softness. There are no appreciable chemical differences between ozonized and non-ozonized alcohols. It is only through the use of MgO that modifications are obtained, chiefly with regard to the acids, and, if the dose of ozone is increased, on the superlative alcohols. Aromatic substances are not affected.

(2) Wein u. Rube XI, 480, 1930. [SOS I may have to double check this citation because the page is blury.]

Oxygenated water.

Chauvin (3) found that the action of hydrogen peroxide was very irregular depending on the composition of the spirits and the dose of reagent used, but that in general there was an increase in esters and especially aldehydes, a decrease in furfurol, dry extract and color as a result of the destruction of tannins (caramel is little or not attacked) and, from an organoleptic point of view, disappearance of bad tastes and improvement of flavor and bouquet. We give below the results obtained by treating a sample of rum with variable doses of chemically pure, commercially pure hydrogen peroxide, low acidity and 12 volumes of oxygen. The analyzes were made after storage for 10 days and 30 days in 340 cc bottles, hermetically sealed.

(3) Mou. Sc. Quesville (4), XXIII, 567, 1909; XXIV 12, 1910.

All the samples still give in a very intense way with gaiacol the reaction of oxygenated water after 30 days of storage. When tasting, the product has a very fine bouquet (in spite of the very large quantity of aldehydes formed), with a tendency to approach grape eau-de-vie, but it resumes in the air the particular smell and flavor of rum.

The same treatment applied to a commercial grape eau-de-vie gave the following results after 30 days of storage:

For low doses of hydrogen peroxide, there was a decrease in the level of the esters and an increase in that of the higher alcohols.

Permanganates and various.

Permanganates of potash and lime have often been advocated for the improvement of spirits. Chapman and Smith observed as early as 1867 that under the action of potassium hydroxide permanganate in dilute aqueous solution, ethyl alcohol gave rise to small quantities of acetic aldehyde, acetic acid, and oxalic acid. Impurities are more easily attacked than ethyl alcohol (Barbet).

Maumené (1) used one of the first permanganates for the purification of alcohols and wines. He advises adding the aqueous solution of MnO4K while stirring, so as to obtain an intimate mixture. Black brown flakes of Mn oxide are produced which can be separated after standing by simple filtration. Bad tastes disappear. The treated red wines do not lose a significant proportion of their color, or even their bouquet, which gains in finesse.

(1) C. R. CXIX, 1894.

Lavolley and Bougoin (1900) advocated treating alcohol with an alkaline earth permanganate (lime permanganate, for example) in the presence of electric current. The operation is carried out in an electrolyser tank without porous partitions. The electrodes may be zinc. The electric current is maintained for 10 to 20 minutes, stirring continuously.

According to a patent of the “Florida Cane products Corporation” (1934), newly distilled spirits, placed in a charred oak barrel, are supplemented with a suitable quantity of sulfuric acid and potassium permanganate in aqueous solution. The bung is then put in place and maintained at a temperature of 48-49° C for 2 days for rum and brandy, and 3 days for whiskey. Aldehydes and higher alcohols are partly removed, while esters are practically unaffected. The carbonized layer of the barrel also absorbs certain impurities. Hydrogen peroxide is then added to lighten the color and delay the transformations. After that, their store in barrels for 6-8 weeks for rum and brandy, 6 months for whiskeys. At the beginning the temperature must be  higher than the ambient temperature and then be lowered gradually. In this way they would obtain eaux-de-vie with the bouquet and softness of the products subjected to 4 years to natural aging.

According to Krzyzanowski (2), oxidation by permanganate would give very good results, as regards both the flavor and the smell of rectified spirits. Sodium dioxide would have a similar action, but even more accentuated. The aldehyde content is reduced by about 60%.

(2) Przemysl. Chem. XXII, 171, 1938.

According to Valaer, permanganate is often used in Puerto Rico for the rapid aging of rum. This author gives the following composition of a rum just distilled on the one hand (a), treated with potassium permanganate and oxygenated water in oak casks and diluted to the merchant level (b):

As other oxidants, sodium dioxide has also been proposed; hypochlorite of lime; potassium chlorate and hydrochloric acid; dichromate of lime and sulfuric acid; manganese dioxide and sulfuric acid, etc.

Catalytic oxidation.

The oxidation of alcohols in the presence of catalysts, after giving rise at the beginning of the century to several patents (Petersen and Schepelern, Schlichting and Kohn, Pozzi-Escort, etc.) has been the object in recent years, of works which suggest interesting possibilities.

In the process recommended by Pozzi-Escot (1905), eau-de-vie is oxidized by air or pure oxygen in the presence of various catalysts (iron oxides, copper oxides, lead oxides, porcelain charcoal etc.), the most indicated of which appears to be platinized asbestos. These are arranged in baskets with perforated bottoms, placed inside a column surrounded by a double jacket, to allow adjusting the temperature of oxidation by means of hot water or steam. The eau-de-vie, contained in a tank under pressure, is sent under pressure to the top of the column, by a tube pierced with a hole for the aspiration of the air. It traverses the column from top to bottom and then goes into a pasteurizer-esterifier constituted by a closed container, in which is placed a small diameter steam-heated coil. The liquid is finally cooled and the vapors condensed by passing through a refrigerant.

Toth (1), in 1929, found, by acting upon mixtures of one part ethyl alcohol and water, and of another part ethyl alcohol and acetic acid on finely divided nickel-titanium copper oxides, that the oxidation began to occur at 150° and above 200° appreciable quantities of aldehydes and acids were formed. The same author, treating in this way the vapors of eau-de-vie, obtained an important improvement of the bouquet. The optimum temperature varies between 150° and 180° C.

(1) Magyar Chem. Folyoirat XXXVIII, 124, 1932.

Von Sandor (2) has recommended that alcohol vapors, mixed with air, should be passed through a glass tube containing the catalyst heated to 100-200°. This method has the following advantages over the Pozzi-Escot process: increased catalyst action time, the activity of which is rapidly lost in contact with liquids; acceleration of the oxidation and esterification phenomena: possibility of removing any trace of the catalyst from the treated liquid.

(2) Z. Unters. Lebensm. LXIII, 333, 1937.

Von Sandor experimented as catalysts the oxides of different metals (copper, lead, tin, nickel, silicon, cobalt cerium, vanadium, molybdenum titanium), obtained by burning in oxygen of pumice, previously dipped in a corresponding metallic nitrate.

We reproduce below some of the results obtained by the author with various eau-de-vie, before and after catalytic oxidation:

The processed spirits had a sweeter and more pleasant flavor than primitive spirits.

The results obtained show that the impurity coefficients are little modified; that the total oxidation coefficient and the true oxidation coefficient are increasing; that the sum of acids + esters, as well as the higher alcohols, decrease. As far as taste improvement is concerned, the oxides of lead, copper, nickel, molybdenum, cobalt, titanium and silicon are the most interesting.

Various processes of purification and aging

In addition to the chemicals already indicated, various reagents (sulfuric acid, carbonate of potash or lime, ammonia, etc.) have been used to purify or age eaux-de-vie, as well as many empirical recipes.

Sulfuric acid.

Sulfuric acid has been and is still sometimes used in very small quantities (1%), to develop the bouquet of spirits. It speeds up the esterification reactions considerably. It is also used to saturate alcohols containing ammoniacal bases from fermentations or defective distillations. The presence of free sulfuric acid in the eaux-de-vie does not necessarily indicate an addition of this product to alcohol. When the musts contain sulfur dioxide, this gas can pass into the distillate and then undergo a slow oxidation, which converts it into sulfuric acid (Valaer).


The carbonate of potash or of soda is used to neutralize the free acids existing in too great proportions in spirits coming from the distillation of acetified musts. It is necessary to avoid making the liquor alkaline, by using alkalis which give aldehydes from bitter materials and offensive odors, the one can not rid from the alcohol.

To correct the taste of newly distilled spirits and give them an antiquated character, a little ammonia (20 to 25 grammes per hectolitre) is added frequently, alone or mixed with other aromatic substances. Am acetate is sometimes also used.

Ammonia treatment should be applied with measurements, because it removes from the spirit a portion of its mellowness, the “dry”. To restore the softness, sometimes a little saccharine (about 05 gr. Per hl.) Or glycerin (5-6 gr. of pure glycerine, concentrated at 30°, per hl) is added. [Ammonia would decrease the acidity and therefore leave the spirit “flabby” no distinct gustatory feature. Sweetness becomes the new chosen feature.]

Finally, it should be pointed out that in the old days, to give eaux-de-vie the smoothness that characterizes them when they are old and of good quality, mucilage of gum adragante and white soap. [gum arabic]


In order to get rid of the aldehydes, it has been proposed to treat the spirits with phenylhydrazine sulphonate (Hewitt): aniline phosphate, at a temperature of 110-120 ° (Mohler) (1); or alkaline bisulfites (Guignard), which together with the aldehydes form crystalline compounds which are poorly soluble in alcohol and in water and can be separated by decantation or filtration.

(1) Mohler gave analysis showing that there would be by this treatment, total removal of aldehydes and bases.

Rousseau, Chanterac and La Baume (1889) add first to the alcoholic liquid, until a neutral reaction and mixing well after each addition, small amounts of an alkaline tartrate (potash or soda, or better salt of Seignette). After deposition of the impurities, which requires a few hours to several days depending on the conditions, a quantity of hyposulphite Na or Ba is introduced, equivalent to about one third of the tartrate employed. The liquid is well mixed and left on its own until the clear part can be decanted. The bouquet of alcoholic beverages, particularly that of rums and wines, would be by this treatment greatly improved.

Silver. [argent]

Beavens, Goresline and Nelson (1) used ionized silver for the aging of eaux-de-vie. The laboratory apparatus used by these authors consisted of an ebonite container containing silver electrodes between which the liquid to be treated is passed. The ionized silver solution was obtained by determining an electrical potential of about 1.6 volts between the electrodes. The current intensities, during the tests carried out, were 0.8-0.12-2.5 milliamperes and the liquid flow velocity of 15-18 liters per hour.

(1) Ind. Eng. Chem. XXIX, 623, 1937.

Processed eaux-de-vie have no detectable chemical differences compared to controls, but the taste and bouquet are considerably improved. The bitterness and greenness of the young spirit disappear and give way to a mellow, sweet and delicate flavor. When the eau-de-vie is treated at 45° C, or is subsequently kept at this temperature, the results are less good; but they are equally satisfactory and not very different from each other, if the operation is carried out at 15° or at 25° C. and the product preserved at 0°, 25° or 35° C. After a stay of 11 months in bottles, the flavor of the treated eaux-de-vie was the same as after a week of storage.

Meat — Yeasts.

A process commonly used in English Guiana to improve distilled rum is to introduce into the storage containers a piece of fresh meat (2 Kgs per hl.), Which is suspended with the help of a string. After a fortnight, the meat is removed. The rum thus treated is softer and more mellow.

Gonville (1912), to improve the bouquet of eaux-de-vie and other alcoholic drinks, advised to add, to a suitable vehicle (flour, sugar, yeast, etc.), beef extract. concentrated and clarified. Depending on the nature of the chosen vehicle, the product can be introduced into fermentation tanks or storage containers.

In order to eliminate the aldehydes, and more particularly the furfurol, Norman (1902) proposed to use a mixture of albumin and magnesia, which would exert a selective action vis-a-vis these impurities.

Rousset (1908) advocated, to develop the bouquet of vétusté in wines and alcohols, to mix them with moist yeast (100 to 1000 gr per hl.) The operation is done in a closed vessel, stirring for 8 to 12 hours. The yeast is then separated by decantation and, in the case of spirits, the liquid can be distilled again. The bouquet produced depends on the yeast race used and the duration of mixing. [I of course did this with marmite many years ago.]

More recently, Barbet (2) has also suggested that in order to incorporate vitamins in the spirits, fresh lees should be treated with low alcohol and then vacuum distilled.

(2) Mém. Soc. Ing. Civ France XO. 793, 1937.

Cousins (1906), to enhance the proportion of naturally occurring esters in rum, recovers aromatic products remaining in the lees of stills, bottoms, etc. These liquids are neutralized with lime and evaporated to dryness. The dry extract obtained is introduced into the spirits (generally the “high wines” or “low wines” collected in the Jamaican distillation method). A slight excess of sulfuric acid is added and the mixture is stirred gently for 12-24 hours to promote esterification. The liquor thus treated is filtered, if necessary, then distilled. By this process, it would have been possible to obtain rums of up to 3500 gr. esters per hectolitre of alcohol at 100°. [Note that this is included in the chapter on artifice.]

It should also be noted that in the past, when legislation on the protection of natural spirits was less stringent in Europe, from the lees of wine, especially in the Rhine valley, an essence of Cognac was made, intended to raise the bouquet of eaux-de-vie and to make imitation cognacs. The liquid lees were subjected to distillation by direct heating or passing a stream of steam. The crude essence, generally colored green with copper and containing a high proportion of odorless free fatty acids, was sometimes purified by stirring with a solution of tartaric acid (in order to remove the copper), then by treatment with a solution of sodium carbonate. The product was subjected to further distillation. In the undiluted state, this essence of cognac has a staggering and unpleasant odor.


Finally, to communicate young spirits a character of vétusté, or accentuate their bouquet, we used many sauce formulas.

Zizine, for example, indicates the following formulas used formerly in Martinique for aging rums:

The quantities above are per 1,000 liters of brandy. As far as prunes and almond hulls are concerned, there is no definite dose, the quantities varying according to the quality of the rum to be obtained and the taste of the operator.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

search previous next tag category expand menu location phone mail time cart zoom edit close