Confidential: Instruction For Making High-Ether Rum by H.H. Cousins (1906)

Follow along: IG @birectifier

This is a blockbuster document, but my goodness does it need a preface and annotation. It is dangerous to have snippets of ideas here running amok without contextualization. For starters, there are only three known copies of this document. One was in the Berlin Public Library [retrieved courtesy an amazing blog friend in Austria], the second was in the Jamaica National Library [retrieved courtesy another amazing friend on the ground in Jamaica and the gracious JNL], and the third was/is in private hands seen by a few people but unshared. As I’ve remarked before, the author Herbert Henry Cousins was a character and noted for writing in a “lucid style” by Nature in 1910:

This lucid style almost makes it look like I made some errors transcribing it, but a few odd choices of language and conjugation are all Cousins.

I also finally found Cousins’ obituary from Nature. Be sure to also track down Cousins’ post card collection and texts on gardening.

My guess is that this “confidential” document made it to Berlin (1928 (re)printing date, but 1906 writing date at the very end) to support Jamaican sales efforts. Some buyers were skeptical of the fairly new Jamaica High-Ether technique and by explaining the process, Cousins dispelled notions of artifice and fraud. There was not much fear of the process getting out there because the economics are a challenge despite the efficiency claims. What Cousins describes is a very expensive way to operate. Many could replicate the distillation method but they didn’t have the corresponding ferments to make it worth their while. Cousins may also have been successful protecting his method with a patent.

[It turns out it made it to the Berlin library from the estate of sugar technologist (and blog hero) Hubert Von Olbrich. But it does not appear in his bibliography of rum production.]

The first third of the document is basically a sales effort with possibly some lobbying thrown in. It almost appears that Cousins was lobbying for a 200 Ether standard. If rum came to be defined by an ether minimum, Jamaican marks would be the premier way to grade-up deficient patent still rum.

Where is rum oil in all of this? Well, for starters this time period is the very beginning of those investigations. Ordinneau around this time was among the first to acknowledge it in Cognac followed by Karl Micko in Germany who invented the birectifier method. Jamaica did not have the techniques yet to examine rum oil so everything was just attributed to esters. They were also caught up in regulations. Esters, at the time, you could count and therefore regulate, rum oil you could not. Ester emphasis which everyone knew was flawed, protected the more mysterious nature of their success. Many of the things the Jamaicans did to increase esters also increased rum oil so they had no incentive to look beyond and drop the ester standard. The technique, however, does depart a bit from rum oil with muck and the high-ether process and we’ll get into that later.

In my Alcohol School lecture on Grand Arôme rums this past October in Jamaica, I called the High-Ether method a cheater process and attributed it to the consolidation of the various diverse Grand Arôme processes (pineapple disease anyone?). I stand by that. At the same time, it is also a noble method that deserves top dollar and a place in the market. It becomes a cheat when you don’t earn it and don’t learn how it fits into the larger rum puzzle of corresponding ferments, still designs, blending, and élevage. It only becomes noble when you’ve done your home work, your experimental legwork and/or it is a deep part of your heritage. The process is simultaneously very special and a cheat. We also cannot let it distract us from reviving other lost methods.

High-Ether rum is slightly foolish because it is plagued by a gross surplus of ordinary ethyl acetate (and no guarantee of extraordinary sensoriality when applied to a blend). Smart-Ether rum is what we need! Nothing in this document is the current gold standard because it represents the very beginning of larger inquiries. What we have here is simply a starting point.

H.H. Cousins starts by importing 50 acid titration burettes to Jamaica and funny enough I just got myself one. If you’re not titrating and learning about acidity, you have no business playing with this method (which can even be dangerous due to the concentrated acids).


Making High-Ether Rum
H.H. Cousins,
Island Chemist
General Principles

The Flavor and Smell of Jamaica Rums are principally dependent on the presence of certain characteristic.


Our rums are superior to most other rums produced in the world and are characterized generally by a higher content of Ethers. This is especially marked in comparison with rums produced by quick fermentation without dunder and distilled in patent continuous stills, such as Demerara rum.

We produce in Jamaica the following classes of rums each specifically adapted for a special trade.

Class I.

Drinking rums for local consumption. These are light rums that age quickly and are, as a rule, too light in body for the English market where they bring 2d. to 4d. per gallon less than rums of Class II.

I would take as a very fine illustration of this class of rum, Appleton rum famous in Jamaica as a fine drinking rum. This rum has a content of a little over 200 parts of Ethers and a has a pleasant, mellow flavour.

The Vere rums are also many of them of this class and command a ready sale in the island. These rums result from low settings and age quickly. They contain from 180 to 250 parts of Ethers.

[Low settings implies less osmotic pressure and saccharomyces yeast over schizosaccharomyces yeast.]

There are also some good drinking rums produced on the North Side, some as low as 100 parts of Ethers but of very pleasant taste and quality.

As quick ageing is the chief factor for the local trade, it does not appear desirable to increase the body of these rums. Good stillhouse management and the production of a high yield of a light pleasant-flavoured spirit free from dry and harsh taste is the chief requirement. I do not advocate any attempt to increase the Ethers in this class of rum for local consumption.

When, however, these rums are exported a difficulty arises. A Jamaica rum with only 100 Ethers could not be distinguished from a good Demerara or a blend of high grade Jamaica and Demerara, except perhaps by an expert in tasting rums and even then the human estimate could easily be at fault.

It is desirable that these rums should not be exported as Jamaica rums at this low standard of Ethers because they lower the standard of trade and reduce the blender’s standard to that of a low minimum. This has two effects, one a depreciation in the value of genuine high grade Jamaica rums and secondly a reduction in the proportion of Jamaica blending rums used by the merchants to grade-up the patent still rums low in Ethers.

Jamaica has at present a monopoly of Ethers in rum and any means of raising the ether standard in commercial rum for general consumption will react to our advantage in the competition for the world’s supply of rum.

[Cousins plants the seed for legal standards that benefit Jamaica.]

A standard of 200 parts of Ethers has been proposed by Dr. Wiley, the United States Government Chemist and by chemists in England. This is a standard readily attainable in Jamaica if there be reasonable fermenting space, without adopting special methods, while the grading-up of any portion of the crop below this standard can be readily accomplished by making a few puncheons of High-Ether rum. Say that the rum for the crop only averages 150 parts of Ethers, a low standard, one puncheon of a 3,000 Ether rum would serve to grade-up 60 puncheons to the standard and the extra cost of manufacture to the estate would not exceed 20s.

[This makes you wonder if Cousins knew Dr. Wiley personally because that would create a link to Harris Eastman Sawyer, the architect of New England Rum at Felton & Sons. Ideas could have flowed in both directions, but that is extreme speculating.]

Class II. Good drinking Rums for the English Market.

These rums are marked by a characteristic fruitiness or mellow body. Trade experts rightly say that Ethers do not constitute the commercial value of rum. Cases can be quoted where a rum of 110 Ethers from Westmoreland will bring 3d. or 4d. per gallon more than rum of Class I at 300 parts of Ethers. It is entirely irrational to maintain the position that the actual content of the total Ethers in a rum measures its commercial value.

[What is thrown in here is the difference between ordinary ethyl acetate and higher value longer chain esters as well as the rum oil wild card.]

To explain this point it is necessary to say something of the chemistry of the Ethers in rum.

(a.) What is an Ether?

When lime or soda are added to an acid they combine with the acid neutralizing its acidity and producing a salt.

Alcohol (the chief component of rum) reacts towards acids in somewhat the same way. If an acid, fermented liquor be distilled, an appreciable combination of the alcohol and acid results. The product of this combination is volatile, comes over in the distillate and imparts to it a fragrant smell. The alcoholic salts of organic acids found in rum are called “Compound Ethers” or shortly “Ethers”. To distinguish them from anhydrous alcohols or Ethers proper, such as ordinary Sulphuric Ether of Sargery, Chemists call the compound Ethers, Esters.

[Here we finally find the difference between Ether and Ester!]

It should be understood that the terms “Ethers,” “Compound Ethers,”and “Esters” as applied to rum all mean the same, viz. volatile alcoholic salts of organic acids.

(b.) What conditions favour the production of Ethers from alcohol and acids?

The chemistry of Ether production is very simple:

Alcohol + Acid = Ether + Water.

The action, however, is incomplete because it is readily reversed:

e.g. Ether + Water = Alcohol + Acid.

[Remember, esters break sometimes as readily as they form.]

Given a certain amount of alcohol and acids in a watery liquid, as in the manufacture of rum, there will always be a certain maximum amount of Ethers that can exist at any time dependent upon:

(1) the relative proportion of alcohol and acid.
(2) the time in which they have been able to react.
(3) the relative proportion of water in the liquid to the Ether produced.
(4) the temperature.

[This sets us up to manipulate each variable.]

General Laws of Ether Production.

(1) The higher the acidity of an alcoholic liquid the greater the amount of Ethers produced: e.g. A common clean wash at 1% acidity will yield a 200 ether rum, whereas a Trelawny liquor at 3% acidity will give a 1000 Ether rum.

(2) The less water in proportion to spirit present the more Ethers produced: e.g. a certain amount of acidity will give ten times more Ethers in the high wines with 60 per cent. alcohol as compared with liquors containing say 6 per cent. of alcohol.

[With a double retort system, you recycled separately both high wines and low wines. Many would think this is heads and tails, but according to Kervegant, this is actually high alcohol tails and low alcohol tails. So two tale fractions. The low wine fraction is much higher in volatile acids that the high wine fraction. The heads fraction is often nothing more than collected in the demisting test and recycled right into the wash boiler.]

(3) The production of Ethers is slow and takes time. Five days are required at the ordinary temperature for a full production of Ethers in a liquid.

If heat be applied, however, the action is greatly expedited.

Where German rum are made containing 1,000 Ethers and more, it has been found an advantage to add acid material to the dead wash and leave it for some days to react. In the case of High Wines I have found 24 hours to be the minimum time necessary to secure a good yield of Ethers from acids and 48 hours will result in a yield of perhaps 25 per cent. more Ethers in the rum produced by distillation.

[It is hard to say here if he is adding high wines back to the dead wash before it is queued for distillation or if he is talking about spiking the high wines with extra acids extracted from the low wines.]

(4) The presence of a little Sulphuric Acid encourages Ether production.

About 2 lbs. in 100 gallons of High Wines to which acids have been added is a desirable excess of Sulphuric Acid to maintain where a high yield of Ethers is desired.

[Many have thought of dropping acidity with sulfuric acid in a dead wash pre-distillation, but it actually destroys other finer aspects of the aroma. True, you increase esters, but you lose other harder to quantify components. Sulfuric acid in the wash and the retorts is a dead end, but it did kick off other avenues to get a similar effect which is what this paper is all about.]

(c) What are the Ethers in Rum?

Jamaica rums as analysed in the Government Laboratory appear to contain:

Acetic Ether       ..     ..   97 %
Butyric Ether     ..      ..   1 to 1½ %
Higher Ethers    ..     ..   ½ to 1 %
Formic Ether      . .    ..   traces.

Expressed as percentages of the total Ethers.

Let us consider these in detail:

Acetic Ether.
This forms the chief ingredient of the Ethers of rum. It is with the exception of Formic Ether which is only present in traces, the most volatile of the Ethers of rum and boils at a slightly lower temperature then alcohol. It is on this account that planters say that poor cooling arrangements result in great loss of Ethers. The first runnings are often very rich in Acetic Ether and undoubtedly a great loss of Acetic Ether takes place in rum is distilled hot or exposed freely to the air.

[Distilled hot would refer to insufficiently condensed.]

Acetic Ether has a pleasant fragrant smell and gives a pleasant taste to rum. When present in excess it stings the nose when smelling rum in a glass and is called by the trade “pepper”.

[WP 502 is a grand arôme rum bottling that in its unblended state clearly has surplus ethyl acetate.

By itself, Acetic Ether is of very small value as a rum flavour. It is so volatile that when exposed to the air for a few hours a glass of rum will lose the greater portion of its Acetic Ether. Again, when the rum is broken down with water the smell is almost entirely covered and the fragrance is lost.

[This volatility is a fascinating thing. You would think a surplus would leave with the angel’s share because of its volatility, but that does not seem to happen. Gary Spedding explains that increases in ethyl acetate during maturation in barrels may come from the breakdown of hemicelloses:

It is said that until the acidity in the barrel reaches a certain level (not specified in the earlier literature – the Liebmann papers from ca. 80 years ago) the other maturation reactions won’t work. One source of acetic acid build up is the breakdown of hemicelluloses – each 7-10th residue in hemicellulose is an acetic acid residue.)

Learning more about these mechanisms is going to be key for maturing grand arôme rums produced with large surpluses of ethyl acetate. Gary also gives us a big clue about Arroyo’s claims of building rums that can mature faster. If the spirits enter the barrel with appreciable noble acidity, they may not have to wait for hemicellulose to break down to drop in pH.]

An increase in the Acetic Ether content of a common, clean or even a high-class rum, if not supported by an increase in the other Ethers in suitable proportion will not add to its intrinsic commercial value.

That is the meaning of the trade dictum “rums are not sold on Ethers.”

On the other hand, it has been shown that nearly the whole of the Ethers of rum consist of Acetic Ether and therefore the economical and regulated control of the production of its Ether is of importance to all producers of Jamaica Rum.

[Ester numbers may just be well correlated to other hallmarks of quality like rum oil.]

How is Acetic Ether produced?

Acetic Acid results from the oxidation of alcohol by the vinegar ferment.

In the common, clean process an abundant supply is produced by the spontaneous acidification of the wash which occurs during the alcoholic fermentation.

In the preparation of the Westmoreland rums, the skimmings are allowed to sour before being used, while in the manufacture of flavoured rums a special acid cistern is kept going for a supply of this material.

For economy, it is desirable when making flavoured rums to operate a special series of fermenting vessels for the efficient production of Acetic Acid.

If cane juice or skimmings be soured directly, only about 1/3 of the acid produced is acetic, the greater proportion, about 2/3, being lactic and other non-volatile acids that can not enter into the composition of rum. It would save material, therefore, to run a special “quick vinegar” process. Set up some weak liquor without dunder at say 14 or 15 Arnaboldi or 10° Brix and let it attenuate to “water”. Then allow this to flow through wooden vessels 4 feet square and 4 feet in depth packed with wooden shavings resting on a perforated false bottom. A series of holes round the lower edge of these chambers admit air. A false lid some six inches below the top of the vessels is filled with say 12 1-inch holes armed with short bamboo tubes for ventilation, while every square inch a small hole is bored through which cotton waste is drawn so that the liquor will drop slowly all over the upper surface of the shavings.

[This is a big hole in our current knowledge. Do vinegar process rums currently use the quick vinegar method? Or, was this just an idea that eventually failed to produce quality. Direct souring means that alcohol production and acetification happen simultaneously almost like kombucha and lots of things can happen in between like lactic ferments or possibly even chain elongation. Really gnarly stuff can also happen like the mucilaginous ferments. Quick vinegar or even the slower Orleans process is sort of like alcohol up and then acetification down. The specifics of what is currently practiced is not known, but I did explore analyzing vinegar with the birectifier.

By this means a quick and economical production of vinegar is assured.

Butyric Ether.

This Ether, when prepared from sugar cane materials is of a pleasant fruity odour and a very desirable constituent of all rums of good body and bouquet. A broker in London would call a rum that was rich in Acetic Ether and well supplied with the heavy body and fruit Ethers “stalky” if no Butyric Ether be present.

The artificial and chemical Ethers of commerce always contain some unpleasant product and therefore artificial Butyric Ether can not be successfully in rum. The impurities from the Butyric fermentation of cane products have both a pleasant odour and taste and are all desirable constituents of rum.

[The extra impurities from the Butyric fermentation may actually be a source of rum oil in Jamaican ferments.]

Production of Butyric Ether.

Mr. Allan, the Fermentation Chemist, has been studying the butyric fermentation of Jamaica rum and gives his opinion that this presents one of the greatest difficulties that distillers have found in Jamaica in making flavoured rums.

Butyric Acid cannot be made from Acetic Acid but is mainly produced from Sugars and Lactic Acid by fermentation in the absence of air. The dunder produced in Jamaica is always rich in Lactic Acid and rotten dunder will often yield Butyric Acid freely. The thick head forming on such material serves to keep out air and then the butyric ferment can operate. I have been experimenting on this matter and am inclined to the opinion that Butyric Acid should be prepared in a separate process.

Unfermented sugary material, dunder deposit (dead yeasts) and a little marl to neutralise the acid produced together with some surface soil which is rich in butyric ferments should be left to ferment. Also cane trash should be added. A thick heavy scum should soon rise and the conditions for butyric fermentation be favourable. After the liquid is matured, a little Sulphuric Acid, about 3/4 the weight of the marl added, say 20 lbs. per 100 gallons, should be added. A little of the clear liquid should be tested with Calcium Chloride Solution. If no precipitate, there is no excess of Sulphuric Acid, if a white precipitate forms add temper lime carefully with stirring until no free Sulphuric Acid can be detected.

[Surface soil to gain cultures is a known technique and Arroyo explored it extensively, but this may be the first reference to it. What you find will not always be good and may produce a lot of off aromas. Some of these organisms may have metabolisms that produce butanol one way and butyric acid another so you may end up with excessive fusel oil you do not want. Arroyo’s preferred culture eventually did not come from soil. He studied butyric ferments extensively before working on rum which is why he was the right man for the job.]

If distilled with dunder this liquid should yield an acid distillate that is rich in Butyric Acid and of great value for introducing into the High-Ether process.

Butyric Ether boils at a much higher temperature than Alcohol but is volatile and readily comes over with the rum in quantity required to flavour the spirit. It has a pleasant fruity smell, bland and soft, rather suggestive of pineapples. When present in a rum it meets the nose immediately with the Acetic Ether to which is gives substance and soft delicacy of aroma. It mellows the rum flavour and is desirable to a certain extent in all Jamaica rums.

Only 1 to 2 per cent. of the total Ether should consist of the Ether. In Ordinary rums this proportion is controlled by the normal bacterial changes that occur in the distillery.

Higher Ethers.

Smell Hampden rum “pineapple flavour”, Ettingdon rum “fruity flavour” and Cave Valley rum “buttery flavour” and an idea will be obtained as to the varying quality and aroma of the “Higher Ethers.” The Westmoreland rums as a class appear to me to be marked by the presence of an unusual porportion of “Higher Ethers” in proportion to Acetic Ether. Each mark seems to have some peculiarity of character in this respect.

From a careful study of the matter and such limited information as is obtainable in the first chemical studies of such a vast and unexplored field of knowledge, I am inclined to the opinion that the special character of the “Mark Rums” of Westmoreland lie in the presence of desirable Higher Ethers. Our chemical knowledge of these is at present very limited but I have satisfied myself by experiments of London rum-experts—Fiat Experimentum in corpore vili, that these higher Ethers do in fact constitute the “body” and “character” of our high-class rums. So far as our present knowledge goes, the higher Ethers of Jamaica rum are restricted to those of acids of even carbon constitution, e.g.:

Butyric Acid     ..       ..     4 carbons
Caproic Acid    ..       ..     6 carbons
Caprylic Acid   ..       ..      8 carbons
Capric Acid     ..        ..     10 carbons
Lauric Acid     ..        …     12 carbons

the acids of uneven carbon content such as: Oenanthylic Acid 7 carbons (found in Brandy as the Ether), and Pelargonic Acid 9 carbons have not so far been recognized in rum. When we remember that these acids are capable of existing in a large number of isomeric forms and that the forms existing in rum may be peculiar and of perhaps usually desirable quality, and that the total amount of these Higher Ethers in Jamaica rum varies from 1 lb. in 100 puncheons in a common, clean rum to 1 lb. in 10 puncheons in a German flavoured rum, it is at once apparent how difficult is the chemical problem of solving the secrets of the Higher Ethers of rum. In this small trace of matter lies the whole secret of our rum industry, and whether a rum sells for 2/ or for 10/ a gallon chiefly depends upon its content of Higher Ethers. The difference between a Westmoreland mark rum and a very thin rum for local consumption is due to the same difference.

[Notice lactic acid is missing which has 3 carbons. I’m not sure if butyric bacteria converting lactic acid (3 carbons) to butyric acid (4 carbons) would be specifically called chain elongation or not. Parfait, Namory and Dubois give us a wonderful accessible modern paper on these esters: Ethyl Ester of Higher Fatty Acids of Rhums.]

Production of Higher Ethers.

Speaking generally, we may say that the higher acids which give rise to these heavy, fragrant Ethers are the result of the putrefactive fermentation of organic substances such as dead yeast. They are probably produced in minute traces in all cisterns and vessels where dead yeast has settled. The ground cisterns of Westmoreland appear to retain a good deal of yeast-matter in their crevices and some of the fine body of these rums must be due to this source. In making German rums dunder-muck or the coagulated yeast in the refuse from the still is a general source from which “fruity” and “flavoury” material is obtained.

[What isn’t really understood in this territory is how beneficial aroma is gained while related bad aromas like Tufo are avoided. Kervegant pointed to the process of peptonization. It has also been explained that using muck raises fusel oil so it must be partnered with a yeast that is a below average fusel oil producer.]

There is everything still to be learned about this matter and there is no doubt a deeper knowledge of the conditions affecting the production of flavour would greatly add to the pre-eminance and prosperity of all branches of the Rum Industry of Jamaica.

Properties of the Higher Ethers.

The Higher Ethers are oily liquid of boiling point higher than that of alcohol and progressing with the number of carbons present in the acid from which the Ether is derived. They are possessed of most attractive fruity smells. Caproic Ether has a sweetish fruity smell, Caprylic Ether a strong smell of pineapples, &c. &c.

Although of such high boiling point all these Ethers have an appreciable vapour tension and volatolise with alcohol in such proportion as to give the spirit a marked flavour.

They are insoluble in water and if present in excessive amount would render the rum faulty when diluted.

The value of the Higher Ethers is best appreciated when a rum is “broken down” with water. The Acetic Ether then becomes almost unnoticeable, the Butyric Ether quite faint, while the Higher Ethers or body ethers exert an even stronger fragrance then in the strong spirit. The merest trace of Caprylic Ether will dominate a large volume of spirit so as to give it a fragrant smell of pineapples that is very lasting.

One of the problems of the manufacture of High Ether rums in Jamaica is that of securing the most desirable kind and quantity of these “body” or “flavour” Ethers of the higher fatty acids.

Class III.

Special Rums of Medium Ether Content.

Certain estates in the island make rums with from 400 to 700 parts of Ethers that fetch 1s. to 1s.6d. per gallon more than ordinary rums and are used for certain purposes.

Tea Rums are light-bodied rums containing a good deal of Acetic Ether but in addition some delicate and fragrant Ethers of the most pleasing quality. These rums are used on the continent for giving “body” to afternoon tea.

A small dose of such a rum in a hot cup of tea gives off a very pleasant fragrance and modifies that drawback of a cup that, without Ethers, is stated only to cheer.

The market for these rums is limited and they are as a rule produced on estates where they result from the simplest process of manufacture.

Rums of this class should not be altered and all that is desirable is to ensure a regularity in the quality of the delicate aroma.

Other estates make a heavier-bodied rum midway between a Westmoreland mark rum and an “export” or German flavoured rum and these are doubtless used for blending purposes, chiefly in the United Kingdom.

It has been objected that any protection of Jamaica rum in England would result in hardship to rums of this quality. This, to my mind, is not a sound view to take. Any education of the public to understand what a genuine “Jamaica” rum should be will react on the blenders and induce them to be more eager than ever for a supply of full-bodied Jamaica blending rums to bring up that patent still rums to somewhere near the same standard as that of a Jamaica rum.

It is no exaggeration to say that the establishment of a 200 standard of Ethers for Jamaica rum would at once put a premium on good Jamaica blending rums to bring up the patent still rums to a higher standard.

Owing to the absence of a differential tariff on home and foreign spirits in the United Kingdom, it would appear that High Ether rums would be no more desirable in England that are the present German rums and that the standard would only tend to appreciate the value of bodied Jamaica rums of medium Ether Content.

Class IV.

German Flavoured Rums.

Owing to the Tariff Wall which German erects to exclude all foreign competition with home industries, Jamaica rum of the ordinary kind can only have a limited market in that country. Whereas the local spirits pays an excise of 2s. per gallon, the imported Jamaica Rum is taxed 10s.

To get over this difficulty, planters in Jamaica were gradually encouraged to increase the flavour of their rums to such an extent that they could be profitably imported into Germany for blending with silent spirit and enable blenders to produce a “blended Jamaica Rum” saleable at a reasonable price.

Owing to the demand for cheap spirits and the enterprise of chemical manufacture, a large trade in “Artificial Rum” now exists on the continent with which our Jamaica German flavoured rums have to compete.

It may be stated that our German rums vary from 800 to 1,400 parts of Ethers and that their commercial values does not depend upon the actual content of Ethers. Given the same type of Ethers, the Ether Content will measure fairly closely the commercial valuation to be expected. Each estate produces a peculiar flavour and an expert can at once recognise the origin of a sample submitted to him.

The manufacture of these rums is most wasteful of material and although flavours of a very pleasing and desirable quality are obtained in many cases, the output is small and the financial results frequently disappointing.

Speaking generally, about 1/4 of the total fermentable matter is turned into acids in this process. Of this, 2/3 is turned into acids of no service in the manufacture, and finally only 1/40 of the acid produced is recovered and sold in the rum.

[This is where Arroyo and the idea I called suave spirits comes in. The Jamaica process is very round-a-bout. Some of that inefficiency is a big environmental burden they almost cannot afford. The big lesson learned in Jamaica this past fall is they can only produce rum proportional to the effluent they can dispose off. This isn’t a pot/column thing, its a fermentation thing.]

There is therefore a sheer loss of one quarter of the rum-producing material at the very outset, quite apart from the serious losses that occur in the process of fermentation under acute conditions of acidity.

To ensure a standard of 1,000 to 1,200 parts of Ethers in this flavoured rum, an acidity of 2½ to 3% must be attained in the liquor as sent to the still.

[A rule of thumb may be that each percentage point of acid is a point of ethanol that is not produced. When you go from percentage points to percentages a decline of 6% ethanol to 5% is almost a 20% change. Some of these may be distilled as low as 3% ABV.]

The Ethers are then concentrated in the first runnings, while the low wines are distilled separately and yield about 30% of the rum crop as low-wines rum. This latter product usually sells at a little less than an ordinary common clean rum and always has a faint taint of fusel oils. It is thus evident that this process is most wasteful and unless a high price is obtainable for “liquor rum” the proceeds may be even less satisfactory than the manufacture of common rum.

[My understanding is that this sort of inferior “queen’s share” kind of rum made from the low wines stopped being a thing around this era. This also implies that high ester rums also truncated and may just be the front half of the spirit.]

The control of acidity is a point hitherto entirely neglected by the makers of German rum. Every worker in a Jamaica distillery should use a Burette and a standard solution of alkali adjusted so that each unit on the burette run into 10 units of the liquor will equal 1 lb. of acid per 100 gallons. Phenol Phthalein is used as an indicator.

The department has imported 50 sets of these appliances and any manager can have a set with working instructions free on request.

[Don’t forget acid titration can be elaborated with two more steps to become ester titration.]

Class V.

High Ether Rum.

In 1902 the writer requested the Government to ascertain through the Foreign Office as to the conditions of the trade in “German Rum” sent from Jamaica to Germany.

A report was received that the trade was of small proportions and owing to the heavy duty on foreign spirits as compared with local spirit and the development of artificial rum flavours it was anticipated that even this small trade would soon cease.

So energetic are the makers of artificial rum flavours that last year every estate in the island was presented with a small sample of essence of Jamaica rum made in Germany which was recommended for improving our ordinary rums!

While the duty on Jamaica rum remains at 10s. and that on German silent spirit is only 2s. per gallon, it is obvious that we can only compete with the artificial rum by making a Jamaica rum of very concentrated flavouring.

To achieve this end, the writer invented a process which is being protected by Letters Patent in all rum-producing countries by which the Ethers of rum can be enormously increased.

Instead of bringing the acids and the alcohol together in a dilute state in the still, the acids are added to the High Wines in the retort and an advantage of 10 to 1 attained in Ether production.

[The valuable acids are in the low wines, but if you can get them to the high alcohol high wines without dilution, you can change the reaction kinetics significantly. This lesson, remember, was learned from messing around with sulfuric acid in the retorts.]

Planters have often tried adding acid fermented liquid to their High Wines but owing to the reduction of the charge from the dilution resulting from this procedure the outcome was not a practical success.

To get over this difficulty a simple chemical procedure has been worked out that enables the distiller to put the acids into the High Wines without appreciable dilution. A working description of this process is given in the next section.

Commercial Basis of High-Ether Rum for the Continental Market.

We can produce a rum of 4,000 to 6,000 Ethers by adopting the High Ether process on any estate at present making German rum.

Two retorts can be used and the whole crop made into one quality instead of having 30% low wine rum as at present. Without any alteration in the fermentations or the materials used, it is now possible to make a rum of at least 4 times the flavouring power of the present make of German rums, and to increase the output of high flavoured rum by 30%. The extra cost would not exceed £1 per puncheon.

Now consider the commercial advantage of such a product to the German Blender:

In competition with chemical flavourings this product would be worth at present time about 20s. per gallon duty paid. Moreover, the law requires the chemical rum to be sold as “Artificial” or “Kunst” Rum where as the blended High Ether rum would be sold as “Blended Jamaica Rum”.

It is obvious that even if we could sell a 4,000 Ether rum at 10s. per gallon the profits would be enormous.

Is the demand Limited?

So far as I can ascertain, the present “German Rum” trade of Jamaica represents but a very small item in the continental rum trade (only about 1,300 phns. a year.) There is room for a very greatly increased output of high-flavoured rum if we can produce it at a price to compete with the chemicals. This can be done and yet leave a magnificent profit.

The French market has lost 2,000,000 gallons of Martinique rum owing to the volcanic eruption at St. Pierre and this is at present being supplied in the form of essence from Hamburg blended with French alcohol. A great market should therefore exist here.

[Cousin’s 1906 writing date is four years after the volcanic eruption destroyed numerous grand arôme producers in Martinique.]

The High Ether process enables an estate to run a flavouring system quite independent of its ordinary fermentation and by distilling “flavour” separately it is possible to make any portion of the crop into High Ether rum without introducing into the dunder the excess of acids and impurities that bring about slow and poor attenuation.

[This is the beginning of where Cousins starts to get ahead of himself.]

It is suggested that perhaps 10 to 20 per cent. of the crop on many estates could be profitably made into High Ether rum for the continental market, while the main bulk of the rum could be made precisely as at present.



Working Instructions
Operating The High Ether

I. General Methods.

A. The lees.

The lees from the retort, or the two retorts where such are in use, contain acids identical in kind and similar in proportion to the acids existing in the Ethers of the rum which has been obtained from the distillation.

If we can recover these acids and introduce them into the next charge of High Wines we shall greatly increase the content of Ethers in the rum.

N.B. The lees dealt with in these instructions are only the waste liquor from the retorts and not dunder from the still or other waste products.

B. Liming the Lees.

The lees should be collected in a suitable vessel, preferably of wood. Copper is liable to corrosion and Iron is unsuitable for the same reason.

Lime the lees with temper-lime prepared as follows—

Slake the Lime and when it has crumbled down sift it to get rid of unburnt limestone. Stir up the sifted material in water to yield a thick milk of Lime and add this gradually to the lees with stirring until the liquid just gives a pink colour when a sample is tested with Phenol Phthalein. Use care not to add any unnecessary excess of Lime and to exclude lumps of unburnt limestone. If the lees contain acids capable of yielding “good body” an appreciable precipitate of insoluble lime salts will take place.

The Acetate and Butyrate of Lime are soluble while the higher members of the series, Caprylic and Capric Acids, give insoluble Lime Salts.

[This differential solubility is quite key to the process.]

On this account, it is desirable to preserve as much of the sediment as possible when transferring the liquid to the evaporating plant.

C. Evaporating the Limed Lees.

This can be done in an open tayche or a steam jacketed vessel. It is necessary to see that the Lime Salts are not overheated and, at the same time, unless properly dried they will hold so much moisture as to reduce the strength of the High Wines charge.

For convenience and security it is desirable to have the evaporation done by direct steam in a vessel holding say 100 gallons which can be fed from a receiver holding limed lees. It is desirable when the lees are nearly evaporated, to dry the residue with exhaust steam only as high pressure steam dries up the Lime Salt into a hard mass that is difficult to dissolve in the next process and cause much delay.

For temporary work, a small copper steam-jacketed pan to hold 20 gallons is ample. The preliminary concentration can then be done in an open tayche or colour-burning pan. If the whole process is to be done over direct fire, great care will be required towards the end not to burn the Lime Salts. A good plan is to finish the drying by placing the damp residue in bags and drying over a boiler or other hot place.

D. Weighing the Lime Salts.

Every 1[8] lbs. of Lime Salts, if properly prepared as here directed, free from excess of Lime, dry and yet not burnt, will require 10 lbs. of Sulphuric Acid for treatment and will supply 1 per cent. of acidity when added to 100 gallons of wines. The Lime Salts should therefore be weighed so as to guide the operator as to the amount of acid to add.

Roughly, every 1 per cent. of acidity in the High Wines will give 1,000 Ethers in the rum. It is recommended when making High Ether rum to work at 6% (or 96 lbs. Lime Salts to every 100 gallons of High Wines) for the firs still and at 5% for ever successive still where the High Wines from a previous High Ether still are used over again. This will give a rum of 4,000 to 6,000 Ethers in practice.

E. Treating the High Wines.

For a single experiment only, temporary arrangements suffice as follows:—

In a puncheon place the charge of High Wines of known quantity. Then add the requisite weighed charge of dry Lime Salts. For every 16 lbs. of these add 10 lbs. of strong Sulphuric Acid. This can be obtained from America in iron drums holding 1,500 lbs. at a cost of about 7£ delivered. Smaller quantities can be obtained locally in carboys at an increased rate.

This acid is very corrosive and the negroes should be cautioned that it will burn anything it touches. Also it must be added slowly to the High Wines as it generates heat. When the acid has been added, close the bunghole and roll the puncheon about. The hole should be opened occasionally to liberate any carbonic acid gas generated from undissolved lime stone in the Lime Salts. After standing for not less than 24 hours and preferably 48 hours, with occasional rolling and stirrings the contents are ready to be filtered.

Have a frame made of oak staves of hexagonal shape standing on short legs and of size to hold 20 gallons and stand easily inside an ordinary puncheon. Line the bottom and sides of the frame with copper gauze as used for centrifugals or plain 30 meshes to the inch wove wire copper gauze. Prepare a puncheon with cock at bottom and cover to fit tightly over the top with hole in the centre. Stand the filter frame inside the puncheon so that the centre is just under the hole in lid of puncheon.

Then allow the contents of the puncheon in which the Wines and Lime Salts and Acid have reacted to flow into the filter. The Sulphuric Acid unites with the Lime in the Lime Salts producing a thick sludge of Sulphate of Lime, while the acids are set free in a concentrated state in the High Wines. We thus introduce into the Wines nothing but the acids naturally present in the distillate from the still.

The liquid passing through the filter need not be quite clear. So long as it is freed form the bulk of the sludge that is enough. The filtered wine should be stored in an air-tight vessel and used for charging the High Wines retort. Where two retorts are used, the lees from both retorts are used but the wines from the High Wines retort alone are intensified.

Testing Wines for free Sulphuric Acid.

Before filtration of the treated wines, it is desirable to test whether the right amount of Sulphuric Acid has been used. Draw off a clear sample or filter a cloudy one through blotting paper and put a in a test tube.

Add 2 drops of Calcium Chloride Solution, if no precipitate  insufficient acid has been added and a little more Sulphuric Acid should be introduced into the wines.

If only a faint precipitate with very little deposit is produced in adding the test, the acidity is just right. If a large precipitate appears, add Lime cautiously to the wines with thorough stirring of the liquid until a filtered sample only gives a slight precipitate when tested with Calcium Chloride.

If the lees are carefully limed, there will have been no mistake over this and the correct acidity will be assure.

[If you’re not testing, don’t bother trying to practice this method.]



Unless the wines are protected from evaporation during this process there will be great loss of Ethers and the strength of the charge be greatly reduced.

The Distillation.

Proceed as usual. Keep the rum separate from the ordinary make and also the High Wines. The latter should be used for the next operation with the process and will have a lot of Ethers already present. Next time perhaps 4% of acidity = 64 lbs. of Lime Salts in 100 gallons wines would suffice to yield the same standard of Ethers in the rum.

Be careful not to throw away the lees from the High Wine retort as the bulk of the acids will remain therein and save much evaporation for the next experiment.

Systematic Working.

To save labour, certain arrangements are desirable to carry out the High Ether process systematically.

Provide an pump to lift the lees from lees receiver in connection with discharge from retorts to a receiver place at a convenient height above the evaporation plant. Lime the lees in this receiver and allow a steady stream of limed liquid to fall in the evaporating plant.

The plant for treating the wine should be erected in the Rum Store or in a locked room to satisfy the Excise officers. The wines should be delivered by a pump into either of two receivers each capable of holding 4 charges for the retort. While one is being treated, the other can be used. These wines receivers should have a man-hole for admitting the Lime Salts and the Sulphuric Acid and should be fitted with a spindle with paddles that can be turned by a handle or by a bevel-gearing from outside. Below these receivers must stand the filters and below these again receivers to hold the same volume as the upper ones. A pump should then lift the filtered wines to the charging butt which should be equipped with a glass gauge.

Special Procedure.

1. To make common or ordinary High-Ether rum for grading up the crop to a good standard of Ethers.

Evaporate the lees from 8 to 10 stills and introduce into charge as above described. Advice can be given from analysis of Estate’s rum and High-Ether rum as to how much to add to each vat or puncheon.

2. To intensity the body of a Rum by selection of lees Lime Salts.

Evaporate the lees, after liming, until reduce to a small bulk, say 1/10 original volume. Stop the evaporation, scrape all the deposit and filter the muddy

liquid. Collect the insoluble residue which will be the Lime Salts of the “fruity” and “body”-producing Acids and use them for making a High Ether rum. This is recommended for rums of Class 2, where body is the chief thing aimed at.

3. High Flavoured Rums.

It will probably be found in practical working that perhaps only half of the usual amount of acid will be required when making a High-Ether rum from ordinary German rum material while the “flavour” will require to be kept up to a good standard.

4. Improved High Flavoured Process.

A. Setup a good, clean fermentation at 16 to 17 Brix, 24 to 26 Jamaica Sacharometer. Keep dunder, etc, clean and do not admit the flavouring materials into the alcoholic process.

B. Have 1/10 of the fermenting space reserved for making vinegar. Set up sweets only at 8 to 10 Brix (12 to 15 Saccharometer). After attentuation, let them pass through the “quick vinegar” process previously described. 3% of volatile acidity should be obtained in 10 days in this way.

[This 3% is an interesting data point I have not seen presented elsewhere.]

C. Set up Butyric system, sweets, fresh skimmings or molasses, set up weak in a vessel with a little earth at bottom and the liquid filled with cane trash. Add 20 lbs. chalk or good marl to every 100 gallons. After 6 weeks, add 16 lbs. of Sulphuric Acid. Stir thoroughly.

[Butyric acid is first being locked up by the lime and then ultimately released by the sulphuric acid.]

D. Putrefactive or Flavour System. Collect all the dunder muck, dead-wash bottoms, etc., with trash and allow to putrefy. This is a slow process and a large stock should be prepared ahead of crop.

E. Distill a blend of B,C and D with some dunder to obtain the volatile acids. When the still has run fairly low, fill up again with water and evaporate again to get a good yield of the heavy acids collect the distillate and lees from retorts. Lime and evaporate down.
Introduce into High Wines.
Charge still with A as usual

This gives in outline a system of working that the writer believes would enable an estate to make either common, clean or High-Ether rum at will and without involving the serious alteration in fermentation resulting from the adoption of the ordinary process of making high-flavoured rum.

[The ordinary process however, may result in the greatest production of rum oil/rose ketones.]

Final Caution.

The whole of these recommendations are based upon experiments that have only just been made and these methods are of necessity still in the experimental stage. They are, however, considered of sufficient value and significance to warrant a careful study and trial by all managers who desire to improve the commercial value of their rum.

H.H. Cousins,

Government Laboratory,


Dated 12th Feb, 1906.

[1906 JNL PDF]
[Berlin Olbrich Copy PDF]

[So nothing in here has exactly been a secret, but it is described in a way that make all the ideas more clearly understandable. In rum making, it is my belief that fermentation should be emphasized over distillation such as by celebrating the use of fission yeasts and fermentation complications like symbiotic bacteria. Jamaican distilleries have used variations of this distillation process in conjunction with very special ferments that have gotten little comparative attention. If you latch onto this process, because it is understandable, you risk missing out on the mystery of very fine rum.]

[Not many people seem to notice that large amounts of vinegar go into the ferment and yet they avoid a pricked distillate? How could that be? If a ferment got rid of the acetic acid, that would likely imply chain elongation of acidic acid to another longer volatile acid? Is that possible? Is it probable? We hear from Cousins that butyric bacteria has the ability to convert lactic acid into butyric. Another way to get rid of the acetic acid is by turning it into esters, but that is a lot of ethyl acetate. If you keep the high wines concentrated, and recycle substantial acids, can you skew the reaction kinetics enough to deal with all the vinegar? Does anything unique happen to the higher alcohols? Does the skewed reaction kinetics make them more likely to form esters? Who the hell wants all that ethyl acetate anyway? Few will benefit from the full vinegar process that do not have continuous column still spirit to average down all that ethyl acetate. Is there any unique maturation phenomena regarding ethyl acetate that has escaped the literature?]

29 thoughts on “Confidential: Instruction For Making High-Ether Rum by H.H. Cousins (1906)

  1. Thanks much for the interesting information.

    I have experimented with Rum making with lime and sulphuric acid. And with vinegar addition, dunder, butyric fermentation and so on. Liming and sulphuric acid is a very powerful tool, which increases the volatility within seconds. Unfortunately I also recognized that it’s true, that it also destroyes some precious flavors.
    So Cousins method is very interesting for me.

    I write because I have an idea of boosting the esters while the stripping run or, if you have a traditional two-retorts-setup, to boost it in the main boiler, not in the retorts: What about adding sulphuric acid at the final part of the distillation when the delicate flavors, which would get destroyed by the sulfuric acid are already distilled over? Do you have read something about this idea somewhere or what do you think about it? Of course it also boosts the acetic acid, so it’s different than Cousins method, which tries to get more from the other acids. But however a combination would be possible too: Adding sulph. acid at the final stage of the destillation into the main boiler would transport much acids into the retorts, the lees would be much more acidic, what means you would get more lime salts for the next run.

  2. That’s a thought, but the most high value aromas are deep into the end of the distilling run as illustrated by birectifier analysis. At the same time, the real prize may be rum oil (which is also created to a degree by acidity in the still). My suspicion is that likely we should explore some of Arroyo’s ideas such as using a centrifuge to eliminate tufo as well as optimizing to significantly reduce fusel oil so that we can distill as low as possible thus capturing as much high value aroma as possible from the tails. These spirits will also likely mature faster. A lot of the work will be done at fermentation and eventually we need to start keeping track of variables like the delta of acidity so we no how much ester potential there is to invest in long or exotic distillations. If the potential is not in the ferment, there is nothing to be gained.

  3. The birectifier sorts the compounds simply by their boiling points. But a normal potstill sorts them by their volatility in the given situation (what means mainly the alcohol strength). That’s why a normal distilled Rum contains so many high boiling point substances like all the higher esters, acids and alcohols. The boiling point of the pure substances tells nothing about the volatility of a tiny amount of it mixed with much water and ethanol.
    So only because Arroyo found with the birectifier the rum oil concentrated in a late fraction doesn’t mean a traditional distillation will behave same. For me the late distillate of a Rum wash simply smells poor and musty and tastes sour. Yes, the sourness can turn into nice esters, especially together with the higher alcohols of the heads fraction. (with a birectifier they are in the tails, but with a potstill they are in the heads). Perhaps you know the heavy banana esters (Isoamyl acetate) from the Forsyths (Worthy Park) Rums.

    Yes, clarification of molasses. Unfortunately very difficult for a hobbyist. So I am rather searching somewhere else…
    A Rum distilled down to almost drinking strength will always be very acidic. Can’t believe it works for a white Rum. But after a long time in a barrel, who knows.
    To get rid of the fusel oils must not mean to get rid of the fusel alcohols (higher alcohols), because they make the ester profile interesting. Only ethyl acetate and ethy butyrate is boring. Main source of higher alcohols is feeding the yeast with proteins instead of a simpler consumable nitrogen source like ammonium nitrate. And hot fermentation. As you know probably.

  4. The birectifier sorts just like ordinary volatility principles which are a function of boiling point and relative solubility. Many compounds have boiling points well over that of water and at no point is the birectifier operating beyond 100c. A birectifier or any stil with a fractioning column change the volatility of congeners by changing ethanol concentration and thus exploiting their relationship with solubility to move them around in the distilling run. The lower the proof, like a typical pot still, the more spread out and the increased ability to be selective.

    Don’t forgot, the birectifier is a just an analysis tool for counting congeners. Once you get information from it, you have to extrapolate back to the still the distillate came from to understand what was where and how to impact the product for the future. The birectifier differs from a vodka still which has intense fractioning only because it can work on the micro scale and be extremely repeatable relying mostly on energy input to pace output so that different distillates can be faithfully compared.

    When Arroyo found rum oil in the later fractions, now the task is extrapolating and understanding where that would be on a spirits still. The big lesson is that it is less volatile than higher alcohols so it is therefore bound to decisions governing higher alcohols. Higher alcohols cannot be neglected and have to be optimized as much as possible at fermentation and yeast selection. According to Kervegant, muck usage elevates higher alcohols and must only be used alongside ferments that are below average in higher alcohol content.

    When we examine the late fractions of the distilling run, we need to consider tufo as well as volatile acids. Is that acidity mostly acetic acid or more noble volatile acids that are pleasant?

    With a pot still, higher alcohols (fusel oils) can be in the heads when distilling the wash, but on the second distillation, when the alcohol content increases, their position shifts to the rear. They can form esters, but they are also likely to break unless their is enough noble volatile acidity pressuring the equilibrium to keep them in place. This means many can form iso-amyl-acetate in the still, but do they have other features that allow them to hold onto it once the distillate moves toward equilibrium? Higher alcohols are also perceived differently with Amyl being the roughest and lowest value in an ester.

    We’re learning more about practical molasses clarification and liming. Right now I’m establishing best practices for model ferments with a microbiologist but we haven’t published anything yet. It is mostly based on Arroyo’s advice in Circular 106.

    When we encounter rums with acidity, we need to determine whether its “noble”. Rum oil (rose ketones), according to perfumers, have exhibit a perceptual “radiant” phenomenon where they valorize compounds alongside them. Many acids and esters will be perceived as more extraordinary with rum oil. We don’t know much about the state of this in lighter rums because nobody is achieving it. A lot of knowledge was lost.

    Ethyl acetate cannot too easily be compared to long chain esters. Its role is different. It supports them. Its about how much is there and how they build perceptual bridges supporting other congeners. When excessive, ethyl acetate can also spoil everything and that is why many full bodied rums (often derived from Grand Aromes) benefit from being stretched.

    Right now, we have 20 Pombe yeasts to compare from a historic collection. We need to figure out which are low fusel oil producers in general and then how to optimize by yeast nutrition among other variables to hit their potential minimum. We’ve gotten the advice that fusel oil can vary within a given yeast by 30% according to the other factors.

    Cheers! -Stephen

  5. Thanks for the long answer.

    Yes, it was not 100% correct what I wrote about “sorting the compounds simply by their boiling point”. I’ll try again:
    Probably you know this graph from “The alcohol textbook”:
    (If you don’t like such links in the comments feel free to delete it.)
    The situation at the right end of this graph is pretty similar to what one expects from the boiling points of the pure substances. High boiling point compounds are less volatile than ethanol, low boiling point ones are more volatile than ethanol. But at the left end of the graph they behave surprisingly different.

    What does this mean for a birectifier-distillation?
    It means, the high boiling point compounds (and rum oil is a high boiling point compound, right?) remain in the boiler or in the column as long the ethanol isn’t distilled over. Then the alcohol content of the distillate suddenly drops to zero and therefore everything changes. Now we have the rules of the left end of the graph: Many high boiling point compounds suddenly become very volatile. (And the boiling point suddenly will be constantly around 100°C as long there is water in the boiler). So the fusel alcohols and also Rum oil comes over. Which one first is interesting of course, but I doubt it tells much about the behaviour of those compounds in a potstill.

    What does this mean for a potstill plus two retorts -distillation?
    It means, the higher alcohols easily distill over into the retorts. But there, a good portion of them remain until the end of the distillation. Depends mainly on the abv in the second retort at the end of the distillation. But because the lees are recycled again and again, the total amount of higher alcohols will build up continously.
    And the Rum oil? I don’t know. All I know is, that it doesn’t come over close to the ethanol-water-azeotrope. But a potstill Rum distillation is never in this area. And at 0%abv it is less volatile than higher alcohols. But this doesn’t tell much, because at a potstill distillation the higher alcohols are already distilled over when the abv goes down.
    Only a lab analysis could find out, where the largest portion Rum oil distills over. But it seems, it is not 100% clear, for what the lab has to search for. You write that Rum oil is rose ketones. I am not able to have an opinion about it. But of course I am happy that it seems that there are progresses in the research.
    Or sensory analysis could find it out. But the other compounds also change in the fractions. So it seems impossible for me to compare sensorily the Rum oil content from a heads and a tails fraction. The birectifier could help here: It could analyse for example 10 samples of different fractions of a complete potstill Rum distillation and search for the fraction with the highest Rum oil content. If I had a birectifier and had a good contact to a high quality Rum producer, I would contact them and ask for fraction samples.

    Yes, ethyl acetate pure has an ugly glue smell. But without it, a Rum would be like a Coke without CO². The ethyl butyrate alone is very synthetical, like Red Bull, but together with ethyl acetate it gets some complexity. I once mixed a few carboxylic acids with ethanol and a few drops sulfuric acid for a better understanding of them. It was very interesting.

    In summer when I will make a Rum again perhaps I will prolong a stripping run with sulfuric acid addition to get very acidic zero abv distillate. Something like 8%abv wash, 20-25%abv low wines, then adding sulfuric acid and collecting in another container 0%abv distillate. After that I try to add the correct amount of lime to this 0%abv distillate, boil it down, probably not to powder, it would scorch. Then awakening it with sulfuric acid, mixing it to the low wines, distilling it to something like 40-50vol% high wines. And then perhaps again collecting 0%abv distillate to get acids for the spirit run. Yes, I like triple distillation. Three long runs taste better than two short ones to the same final abv or achieving it with rectification IMO.

    Experimenting with Schiz. pombe would be great too of course. But I don’t think I will get it in my area.

  6. …and I am interested in your definition of “fusel oil”. It’s a fuzzy term IMO. “Fusel alcohols” are another word for higher alcohols, which are (simplified) a bad thing except they are esterified. Esterified they are a good thing. Fusel alcohols are a part of the fusel oil. What’s the other part? In general the other part is considered as a bad thing. Both parts you can keep down in the boiler or at the downer part of the column as long you keep the abv very high. But at low abv the fusel alcohols tend to be in the heads and the other fusel part tends to be in the tails, right?

  7. Fusel oil is indeed fusel alcohol or higher alcohols. It is just an older dialect. They are not necessarily good when esterified and considered a flaw in some column distilled brandied (and rums) where excessive higher alcohols build up on a tray. Esters like iso-amyl acetate, in excess, can be plebian and ordinary. They are a reason continuous column distilled spirits can never match pot stills.

    When fusel oil is in the heads is a pretty extreme phenomenon only encountered in the first state of pot still double distillation. Amerine at UC Davis and other authors presented by Kervegant did work explaining the phenomenon. They even add math. A related phenomenon is that of “demisting” where higher alcohols and long chain acids are stuck to the surface of the column and are rinsed out by the high ABV first runnings of the still. For many heavy spirits, the heads cut is only as long as the demisting phenomemon lasts.

    So higher alcohols presenting themselves in the heads fraction of a low ABV pot distillation does not effect production decisions too much. One goal of fraction recycling for these pot distillation runs is actually to average ABV upwards which expands the collectible hearts fraction.

  8. I’ve seen that chart which is often presented to illustrate the volatility of methanol.

    When you consider boiling points, the fascinating thing is the ability for ester to increase the volatility of a volatile acid. A degree of esterificaiton in the still may work to push things out of the way or pull them into the hearts fraction. Not enough is known because we seem to only have chemical analysis of complete spirits and not what is cut away and/or recycled. I have analyzed a few different tail fractions with the birectifier (donated by a commercial American producer) and the results were absolutely fascinating. They merit a lot of further investigation.

    Some distillers of the past noted the importance aqueous “tail waters” and then Arroyo firmed it up in Circular 106 and described a fourth fraction after the tails that had value. We don’t know enough about this and how it relates to the tufo phenomenon. My microbiologist colleague and I are designing a lot of small scale experiments to learn. I have a nice three liter centrifuge that will be used to both explore extreme molasses clarification as well as wash clarification.

    Off to work. Cheers! -Stephen

  9. Isn’t that true for all esters, that pure they smell synthetical? Not especially the esters from higher alcohols, but also ethanol-esters? I think, we need a complex mixture, also including esters from higher acohols. And because there are of course way less higher alcohols than ethanol in a ferment, the higher alcohol esters are harder to get. I don’t think we have to fear to overdo those esters. On the other hand, their odor threshold is way lower as far as I know, so it doesn’t need much of them…

    I don’t think, higher alcohols in the heads is something extraordinary.
    Or at least it’s impossible to get both:
    1. reducing the higher alcohols by distilling.
    2. distilling down at least to barrel strength, so that there is no water addition needed before barreling.
    Looking at the graph (and believing it’s true), the point, where the volatility is “1” is for the higher alcohols at around 40%abv. 40%abv means around 79%abv in the vapor. So if you want to keep the higher alcohols in the boiler, with a potstill you have to hold the abv in the boiler over 40%, or when using a reflux still you have to hold the abv in the upper part of the column over 79%. With a double retort setup you have to hold the abv in the second retort over 40%.
    Double retort Rum distillation is relatively high abv. So here it’s possible to keep the higher alcohols out of the distillate. But then you have a middle cut with perhaps 85%abv. And this of course needs diluting before barreling. And because all higher alcohols made it at least into the first retort, all the higher alcohols get recycled again and again. So they build up and more and more also find their way into the middle cut.
    In a Whisky double potstill distillation or a Bourbon continuous column with thumper distillation you will get all higher alcohols into the heads and the middle cut, because you distill the whole time below 79%abv.
    And it is smellable IMO: Not the tails smell like higher alcohols. It’s more smellable in the heads. And I don’t mean the glue smell from ethyl acetate, which is undoubtely in the heads. It’s something solventy besides the glue smell.

    Here two download-links with scientific papers:
    Table 2 shows the low higher alcohol content of tails compared to the heads and hearts.
    The second graph shows how the amount of higher alcohols is huge at the beginning and then drops down.

    So all you can do is to find a yeast and circumstances which produce less higher alcohols. But then you also don’t get their esters. The cleaner fermentation gives you the opportunity to distill at lower abv. So you get additional “good tails” but a less complex ester profile.
    The opposite would be a dirty fermentation and a higher abv distillation. Less “good tails” but more complex esters.
    I in general see more hope in the second method. At least for abstract spirits like Rum and Whisky. For sure not for fruit brandies.

    Yes, I also have read much about a usable fraction after the tails. There is also a source about such a fraction in plum brandy distillation BTW. So it is not a special Rum oil thing I think. Unfortunately I never found something like this. The distillate there was always only musty and acidic.

    We differ in a few thoughts. Something like a different philosophy. And perhaps I am biased. But I really would like to see your success with your ideas. The more success with other ideas than mine the more I can learn from it.


  10. I have not seen that plum paper which looks like a great read.

    Something to note is that perceptually, a spirit can justify more higher alcohols if it contains more long chain esters and rum oil in its sensory matrix. I’m learning the titrations for acids and esters, but fusel oil titration is looking quite involved. Very tricky to measure before you jump to GCMS.

    We’re on a long road to success. Right now I’m still collecting the literature because I don’t feel I know enough. I’m still expecting two different Arroyo papers that present his understanding of the Jamaica process and I think he confronts ideas like vinegar, and skimmings. Hopefully he will explain why he did not go the route of extremely low pH.

    Kervegant also has a large chapter coming up that looks like it can address some of the stuff we were just discussing. I also found a series of citations that are Jamaica’s reply to Arroyo in the 1940’s J.A.S.T. Journal. This journal is only at the Jamaican national library and I’m trying to get access.

    I’m just about to move into a new house where I’m building a lab. I’ll be able to do a lot more experiments. Since I’m waiting to move, I’m trying to make bigger headway on translating the literature.

  11. Here the plum brandy information:
    They write that they use the last distillate at around 10%abv partially for diluting the 63% middle cut. Unfortunately there is no information, what or how much was between the middle cut and the 10% stuff.
    And unfortunately not everything sounds logical here. They write the spirit run starts at 10%abv, then rises to 70% and then drops down again to 10%…

    Yes, when I remember right, I also wondered, why he uses so little sulfuric acid before distillation. If this is it what you wonder about.
    My washes needed so much lime to hold the pH at around 5.5, I had to use very much acid before distillation. I also had muck buckets: Mixtures from water, dunder, molasses, yeast, vinegar bacteria, cheese (lactic and propionic bacteria) and soil (clostridia). They needed so much lime to keep the pH up and the bacteria happy, and after adding sulfuric acid, the gypsum layer at the bottom was huge… and yes, when adding the acid I recognized not only an huge and sudden rise in fruitiness (mainly ethyl butyrate probably), but also a loss in other flavors.
    During fermentation the flavor of a highly limed wash is really low. Without lime the CO² blows out many nice aromas. If I had more experience, probably I won’t need a pH meter, the smell alone wold tell me the pH. Actually this is what I did after some experience: I only measured pH when I recognized a good amount of fruity flavors. And my nose was never really wrong. If there was no fruity flavors, it was sure, that the pH is still high enough.

  12. I need to re-read the plum paper paper in case I missed a key point, but they don’t seem to account for the “de-misting test” phenomenon where the beginning of the spirits run rinses away congeners from the end of the previous run.

  13. Here two other pdfs with perhaps interesting information about the higher alcohols:
    Here on Table 1 you can see, where in a column with 34 plates the higher alcohols accumulate. At the downer part (low abv) they flow up, but then, when the abv is higher, they are not able to move upwards further.
    Even some hobby vodka distillers experiment with fusel side draws for this reasons. The more fusel alcohols they draw off at the downer part of the column, the cleaner is the spirit at the top.
    Stripping and spirit runs with a relatively low rectifying column still.
    At the stripping the higher alcohols are concentrated in the early distillate.
    Although the spirit run starts over 84% and remains long in the area over 80%, the higher alcohols are mainly in the hearts and also much in the heads. Only little are in the tails. Important: Under the tables is written, that the numbers are not absolute, but relative to the alcohol content. So the absolute numbers will be higher at the early fractions and lower at the late ones.
    Also interesting here is the constant rise of the volatile acidity. It seems there is no late fraction here with something like “sweet water”.

  14. Thank you for all the translation work.

    Finally it depends where we see a higher chance for whatever we are searching for: Either in the methods of today Rum distilleries like Hampden or Worthy Park (hot fermentation, probably no addition of mineralic yeast nutrients, probably unclarified molasses: producing a lot of higher alcohols) or like Arroyo suggested (a more clean “brandy like” relatively cold fermentation with clarified molasses and added nutrients: reducing higher alcohols).
    Of course this is not the whole story about making good Rum, but it is an in general important point, where he differs to succesfull producers of today.

    I wonder how Arroyos story ended. AFAIK Puerto Rico doesn’t have a Jamaican style Rum industry today unfortunately. So for whatever reason he was not successful to help his ideas to break through. But his studies look well financed. Did his ideas come over the small scale experimental stage?

  15. There are still big holes in our knowledge of what the Jamaicans actually do. For one, they use a ton of vinegar and their fermentations may feature chain elongation to change a percentage of the vinegar into longer chain acids. They also produce concentrates that they sell bulk or stretch with column spirit. These are distilled at fairly high proofs yet retain a ton of a flavor. What their recycled fractions look like is a bit of a mystery. Their molasses was also unique because they were connected directly to sugar houses but that eventually changed and therefore ingredients like skimmings went away (which we know to be full of sugarcane wax). There are lots of 1940’s papers regarding their practices and semi modernization, but they are all in the J.A.S.T Journal, which I cannot access yet.

    Its really hard to say what happened with Arroyo’s ideas after his untimely death. A big problem is that they took skilled labour that was scarce. There was a fad of clarifying molasses after Arroyo, even in Jamaica. The post war economy definitely played a role. I don’t think that Arroyo was connected to the Bacardis but the German firm, Specht, who evaluated Arroyo’s Jamaican style rums went on to represent Bacardi in Europe. This document tells Puerto Rico’s story in a broader context:

  16. Cousins suggests the right amount of lime added to the lees before evaporating the solution is when a sample with added Phenol Phthalein gives a pink color. According to wikipedia it needs pH 8.2 to switch from colorless to pink. So he rises the pH to clearly over 7. Doesn’t that mean all acids aren’t volatile anymore, not only the simple ones like acetic acid? I thought something like pH 6 would be a better idea? Do you know what other pH indicators they had at his time? Perhaps this detail is outdated?

    I recently stripped a lime buffered Bourbon wash. At the end of the run I cooled the still down a bit , opened it, added sulfuric acid (a bit more than only to neutralise the lime), closed it and continued the distillation. The distillate has 0% alcohol and a pH 3.5. I will add lime and evaporate it. Probably not to powder, but perhaps to 1/10 of the starting volume. Wonder what pH I should aim for.

  17. Hi there, I give a primer on these issues in a post called Advanced Acid And Ester Titration Basics. It took me a while to figure out why 8.2 is chosen. Even though you are at the equivalence point, the resultant salts in this scenario (weak acid/strong base) retain an ion charge that is overall alkaline. There chosen indicator is still very much effective.

    In that post, I did mess up a few things I intent to fix (working backwards from historic data), but I hope I did the subject justice. Kervegant gives us some even better protocols in his analysis chapter I intend to test.

    Sulfuric acid may not contribute much because there is no alcohol around to participate with esterification. I’m not too sure about what to expect from the pH of a tales fraction. The pH may seem low because this distillate is unbuffered. The titratable acidity may tell you if you have something of value. H.H. Cousins scenario is unique because they have volumes large enough to make the effort worth while. Keep in mind, the ordinary acetic salts are soluble while the higher value salts are not. He separated ordinary from high value just by decanting. When he evaporated, it was mainly to remove water from influencing the kinetics within his retort. Before we even get to that last part, we need to verify there are enough high value acid. You may have to leave a small volume of liquid just to make the material possible to handle at the small scale.

    All these titration skills will pay off in many others areas of production and will help make the jump to accurately measuring esters.

    Cheers! -Stephen

  18. Again I have a question…

    as you write, one of the important things here is the different solubility of the calcium salts.
    I have found a few solubility numbers:

    calcium octanoate/caprylate: 0.00081g/lt 0.001193g/l
    calcium caprate/decanoate: 0.04789g/l
    calcium butyrate 0.7g/l
    calcium propionate/propanoate 31.3g/l
    calcium acetate 35g/l
    calcium lactate 30g/lt 58g/l
    calcium formate 170g/l

    So yes, it looks like it works this way. The less soluble salts will fall out and the remaining acids will evaporate. In the end we have a soup or a powder with a better ratio of the acids and after the spirit run a more complex rum.

    But one thing disturbs me:
    To release the collected acids with sulfuric acid. Calcium sulfate has a solubility of 2.4g/l. This is not very soluble, but more soluble than the precious calcium salts of butyric, decanoate and octanoate acids. So the logic that the sulfuric acids binds to the calcium and falls out while at the same time the precious acids go into solution, looks not plausible for me.

    What do you think?

  19. Ok, I think I got it by myself.

    Sulphuric acid is of course a much stronger acid than those carboxylic acids. A strong acid means an acid that dissociates to ions almost complete. And only ions are able to form a salt. The carboxylic acids don’t dissociate much (even less after dropping the pH with the sulphuric acid), so only few will connect to the calcium and fall out.

    Each acid will have an equilibrium of undissociated acid, dissociated acid, solved calcium salt and falling out calcium salt. And how this equilibrium is balanced depends mainly on the pH what means the additions of lime at the beginning and sulphuric acid at the end of the whole process.

    I personally think that there is a huge loss of acids somewhere in the process. But it seems that the ratio of valuable to less valuable acids rises. So this process doesn’t rise the ester level much but more the quality of esters.
    I think that because the Rum I have made with a similar process to Cousins is not as high-ester than other Rums I have made (for example with simple adding sulphuric acid to the low wines) but has a better quality of its fruit flavors.

  20. Solubility is not the biggest deal. It is only important at the point the salts need to be decanted from the first aqueous solutions. After that when the salts are transferred to a higher alcohol solution and released via the reaction with sulfuric acid, if the molar math lines up, solubility is no longer and issue and volatility becomes the issue. You have free acids you need to form esters by acid catalyzed esterification in a higher alcohol environment.

    What I would do is first slowly add an amount of lime to the tail waters to get to pH 8.2. This should take multiple increments possibly over multiple days because the reaction is so slow relative to NaOH. Then take that same quantity of lime dissolved in water and see how much sulfuric acid it takes to “back titrate” it to 8.2. This quantity of sulfuric acid should be added to release the volatile acids bound as salts. You don’t get the benefit unless you migrate those acids to higher alcohol solution that can drive more esterification.

  21. I fear I have to excuse me for those solubility data I posted. In the meanwhile I found many mistakes. Those are quotes from someone somewhere online. I now checked some values in the international critical tables and found out the solubilities of the calcium salts are much higher.
    It has happened to me often that afterwards posted chemistry online information was wrong. Researching online about chemistry is not easier than about distilling. Strange.

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