Aroma Breakage and Rum Design

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A curious topic that I’ve never seen discussed in other research papers is the topic Arroyo spends a lot of time on of aroma breakage due to diluting spirits with water. Apparently, the sudden shock of adding water to spirits, particularly rum because much of its character is dependent on esters and rum oil, is capable of splitting the esters via hydrolysis and possibly precipitating aromatic substances as salts.

The ideal raw distillate, however, would be one needing no dilution or treatment of any kind before proceeding with its curing, either slow or natural; or accelerated or artificial. These conditions are attainable through proper yeast and raw material selection, appropriate methods of fermentation and post fermentation treatment of the beers; followed by carefully controlled distillation technic based on the principle of selective extraction. Present manufacturing methods with few exceptions, have not come to this high state of development as yet. Hence, mention must be made of the important changes occurring during the diluting, or the diluting and carbon treatment process during rectification.

I was first casually introduced to the topic many years ago by Ed Hamilton who explained to me the phenomenon as a past problem with Martinique rhums shipped to France for bottling. According to Ed, these rhums would be improperly diluted, rushing the process, and the aroma would be detrimentally effected. The science on the topic so far is not as easy to fully explain as I’d like, but there is one overall solution pointed out above and that is to distill at lower proofs so much of the water is already integrated. Easier said than done, lets let Arroyo drop a little more science:

When a freshly distilled rum is diluted, its chemical composition as well as its physical characteristics are affected. The action of the diluent is felt to a greater or less extent, in accordance with: (1) original proof at which distillation took place; (2) chemical composition of the original distillate; (3) nature of the diluent, and manner in which it is applied. The deleterious action of rum dilution is twofold: chemical and physical. The first consists in a dissociation of part of the ester content through the hydrolytic action of the diluent acting in an acid medium; the second operates by salting out or separating certain essential oils through shock, and by the lowering effect on the alcoholic concentration of the raw distillate through the addition of the diluent. Among these oils we have some of the most valuable  natural constituents of a genuine rum. When the raw rum has been distilled at a very high proof, say between 170-180 degrees, a very large amount of diluent must be added in order to bring the proof down, say to 110 degrees. Now, the more diluent added the stronger will its hydrolytic effect be on the esters present in the raw distillate, and the stronger will be the tendency toward separation of essential oils. Hence, the caution previously given in the chapter on rum distillation that rum should be distilled at the lowest possible proof compatible with high quality of distillate. When the original chemical composition of the raw rum in its relation to the process of dilution is considered, it will readily be seen that the higher the free acidity and the ester content of the raw distillate, the faster and the more intense will become the hydrolyzing effect of the diluent on the ester content of the raw spirit. The same holds true on the salting out of valuable essential oils.

Lets stop him for a minute. It appears that the fullest flavored rums have the most to lose. It also seems like little inhomogenous zones get briefly created in the spirit where there isn’t enough ethanol to keep certain things in solution like the rum oil and though brief it is enough to shock stuff out. With the esters it is a little different and my favorite explanation of ester hydrolysis comes from Peter Atkin’s Reactions: The Private Life of Atoms. What I would think is that everything would eventually come back to equilibrium and that would easily re-dissolve the rum oil. I guess it doesn’t happen fast enough and there is a danger of stuff getting left behind when spirits are being only temporarily held in a vat that needs to be turned over for another process.

The nature of, and manner of adding the diluent, will also become a factor of importance during the process of dilution. There are at least six classes of diluents commonly used for this process: (1) ordinary tap water from the city mains; (2) well water; (3) rain water; (4) distilled water; (5) chemically treated water; (6) alcoholic solution in distilled or rain water, previously cured by either natural or artificial means. This last mentioned diluent is the least harmful and best recommended for this purpose, but is the one less used on account of the trouble of preparing and storing under suitable conditions large quantities of these weakly alcoholic solutions. Good practice should restrain the number of diluents to be three of the six mentioned above, and these should include; (1) distilled aerated water, (2) rain water, and (3) alcoholic solutions. Of the two plain water diluents, rain water is to be preferred, as it contains plenty of air and, therefore, lacks the flatness of taste peculiar to distilled water. Thoroughly aerated distilled water has the advantage of being readily available at all time. Diluting with aged mixtures of alcohol and water, or rum and water, will be the best method to follow; but as explained before, this method has its shortcomings especially for the large producer.

I remember reading this and wondering if Arroyo’s ideas like the ethanol-water mixture were arm chair ideas, dreamed up but never tried, or if anyone got it off the ground. Could it be worked into a strategy that would give a small producer an advantage when they typically lack any advantage due to scale? I could see column distilled relatively light rums being easily diluted much under 40% and then average up with stocks of aged, extra heavy, pot still spirit (to protect the pot still spirit which has more to lose). Sadly, I suspect not many small new Continental producers are making anything at risk of aroma breakage or using that template.

Now, whatever the nature of the diluent used, the manner of its application will have considerable influence in the extent of ester hydrolysis, and especially as to the degree of separation of valuable essential oils constituents. Cold diluent, suddently added in bulk or added in a very short period of time, will prove the most harmful. The opposite conditions of applying the diluent, that is, slightly warm, slowly and in an atomized form, will prove the least harmful.

The water so many distilleries use is at the mercy of the seasons. They aren’t really in a position to raise a large volume of distilled water much above room temperature. I suspect the cheap alternative would be to use the still’s condenser as a heat exchanger and warm diluting water during distilling runs. I can’t imagine rigging up a atomizer with an agitator would be too difficult.

In the course of these studies on rum we have observed that the harmful effect of the diluent in rum diluting last over an appreciable period of time, never less than for three moths, and extending up to six months. It is really a very important matter that has been lightly, too lightly, considered up to the present time.

Whatever vats you have, you’d definitely need back sooner than three months and whatever precipitated would not be evenly distributed between the barrels or bottles. Whatever is precipitated could also be left as an oil clinging to the side of the vat. If the tail end barrel did get an appreciable extra quantity to try and re-dissolve it may not do it properly. Many blending practices where spirits are briefly re-barreled after marrying may be related to the concepts Arroyo is presenting. Whiskey’s may have different congener sets, but they may also be subject to similar forces.

Its will be noticed that strong dissociation of the ester molecules occur in every instance after the raw rums have been diluted, and that this state of original esters hydrolysis is not ameliorated even after three months of curing in an oak keg. The ester loss through hydrolysis is heavier in those rums originally high in ester content. Organoleptic tests on the undiluted and the diluted sample are consistently in favor of the former. Hence, rum dilution is really a complicated problem, and the ill effects of dilution interfere also with the proper and expected progress in quality during the first few months of the curing period. If to obviate the ill effect on the curing of the raw rum during the ageing period occasioned by the diluting process, the raw rums are barrelled at the high proofs of distillation, nothing is gained in the long run; for if it true that it will mature quicker during aging in this case, it is also true that its proof must be lowered before it is bottled up. When diluting the cured rum, the effect of the diluent will be more disasterous even than in the case when the beverage was diluted as a raw product. These considerations make the problem of dilution an arduous one. The solution must come during the distillation stage of rum manufacture. Raw distillates much be distilled at low enough proof so that no dilution, or at least very little dilution should be required during rectification and curing. And this must take effect in such a manner that the quality of the commercial rum stall remain unimpaired.

I have a feeling Arroyo was not always popular because he was usually advocating taking the long road and being thorough. To distill rums at a lower proof you’d have to design fermentations worthy of a lower proof. Or you might not have to if you’ve got the time. Arroyo mentions that rum, unlike a whiskey, can be enjoyed right from the still and will have no objectionable roughness like a white dog. On the other hand, Peter Valaer, in 1937 for an IRS survey, describes the legendary extra aged New England rums as being rough right from the still and distilled at 60% which is considered fairly low. Valaer also briefly mentions the use of “pure culture rum yeasts prepared from a single cell in some of the most scientifically controlled rum distilleries” in the U.S. Who knows if U.S. producer’s like Felton & Son’s conducted their own Olympiad to select a champion rum yeast, but it does look like they had the technology. I’m not sure if they used a Pombe yeast because I have not been able to find hints of their fermentation durations which would imply an answer.

Many spirits out there distill at curiously low proofs such as cachaça and many tequilas. They raise the question, are these cruder spirits like the New England rum Valaer describes or are they produced from unique ferments with less objectionable congeners than the average whiskey ferment? The answer is probably the latter. If one tried to optimize a fermentation to distill at a lower proof, what would it look like?

The answer lies in limiting ordinary esters and short chain fatty acids typically separated from the hearts fraction by the heads cut as well as limiting fusel oil which is hard to eliminate during distillation because it risks reducing rum oil. Fusel oil in rums is best reduced by careful yeast selection and then careful optimization of other variables like fermentation temperature with a lower temperature typically correlating to less. Fusel oil production tests were part of the yeast Olympiad I described recently.

Excessive ordinary esters get reduced in the ferment by salting them out. Short chain fatty acids like acetic and formic have a higher affinity for alkaline substances than longer chain fatty acids and thus combine to become non-volatile salts. If this is done with precision, which basically requires analysis and systematic trials, there will be less objectionable congeners in the ferment and distillation can proceed at a lower proof incorporating more water. Extraordinary esters of a lower frequency of occurrence, that form in both the ferment and the still, will suffer less occasion to split apart. New England rums in 1937 may not have been benefiting from the careful pH buffering that Arroyo was using to distill at lower proof. Harris Eastman Sawyer, who I identified as the architect of modern New England rum, sadly died in 1911. Though he was progressive, he was not likely to be that far ahead of anyone else.

By this point, most of you are probably thinking: why don’t you just super fractionate as explained previously, over dilute the central neutral fraction which is taking Arroyo’s advice of diluting with an ethanol water solution and see if that keeps more of the esters together? I didn’t realize it was that obvious, but what is left is to simply put it to the test and see what happens. And to hope the logistics aren’t a deal breaking nightmare.

Even more of you are probably thinking: where is Lost Spirits during these recent revelations on rum design? Lost Spirits has put most all their emphasis on post distillation curing ideas thinking that that is what makes a rum great. Arroyo would probably laugh them out the door. He time and time again explains that you need a distillate worth maturation to even bother, and there is little emphasis on that (so far) in the Lost Spirits camp. You also need to get a well crafted ferment to get a distillate worth a damn. But if you could bring all those things together it may well be more worth accelerated maturation and I hope they do. On the other hand, if you really nailed all those processes, you’d probably not feel the need to accelerate anything.

One of the major things I’m forgetting about maturation is that a significant change, according to Arroyo, during the first legs of curing in a barrel are excessive ordinary congeners, with a high frequency of occurrence, namely ethyl acetate and acetaldehyde, actually evaporating with the angel’s share because they are so volatile. Accelerated maturation techniques, like that of Lost Spirits, have no angel’s share and cannot benefit from this mechanism. If they need the same effect, they’ll have to spend more time with their ferments. If they develop spirits with significant ester contents which is their goal, I hope they are taking all precautions to prevent aroma breakage when they get diluted to drinking proof.

Next up will be Arroyo’s thoughts on curing, he didn’t like the term aging, and the ideas are more relevant now than ever.

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