Month: April 2015

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An interesting article appeared in Wired recently about the accelerated aging techniques being developed at the Lost Spirits distillery. It was flung around the web and possibly shared sixteen thousand times yet didn’t generate much critical comment except polarizing reactionary one liners. I was really disappointed that the spirits industry didn’t take the time to better frame or contextualize what was being done at Lost Spirits because interest in spirits is at an all time high and there are so many supposed experts out there. The claims of the article bring up some real weighty issues. What happens if in six days we can make spirits taste like they’re 20 years old? Can it really be done? How sophisticated were previous attempts? Does more age really make a product more extraordinary at the sensory level? And what would it mean for the industry?

The article made Lost Spirits seem like a sophisticated operation, but taking a look at previous works they’ve published on their investigations (part I, part II) shows a giant lack of involvement, poor research skills, hasty conclusions, gross reinventing of the wheel, and a general naivety. All those same descriptors have been used to describe my work as well so… After reading a lot about Lost Spirits, I hope they keep messing around and investigating things, but I also hope the rest of the industry and people that write about them are better able to frame and contextualize what they are doing. Standards right now in spirits journalism are very low. I really hope to taste the rum and would pay a premium price for a bottle in a heartbeat. Actually experiencing it would help make sure my ideas about aging can scale.

Some of the visceral reactions to the lost spirits article make me think that we haven’t really been able to articulate what aged spirits mean to us. Is it all in their sensory values or is it largely a symbolic thing? Lost Spirits is trying to duplicate the sensory values but they are going to lose all the symbolism and much of the ability to retrieve memories. Were the spirits in oak during the Clinton era? I remember those days. Was it in oak since my birth year? So many people buy pricey birth year products and don’t care if they taste good because it means so much more to them. Do we admire the producer’s patience? Most other businesses erode all foresight to the short run, but distilleries keep massive inventories, think so far out into the next generation and that inspires people whether they can articulate it or not. The spirits and wine industries are an exemplary and vital pillar of long run thought. They are a template we need to maintain if our governments are going to be able to plan for us and future generations. So much of a vineyardist’s career is making decisions whose fruit only the next generation will taste. When those who truly appreciate a wine contemplate it, they think of all it symbolizes and not just its sensory values. All that it can symbolize is actually a large part of the price even though most consumers can’t wrap their heads around it. We all practice very selective forms of aestheticism where we only focus on sensory values. Exclusivity of expensive bottles is a thing, and very cheap to write about, but don’t let its attention whore nature distract you from the symbolic beauty of artifacts of great foresight.

So if we could pull off the sensory values of very old spirits on the cheap, would it really shake up the industry? After spending enough time in the wine business I’d say no. There are manipulated wines of effort and very pure wines of terroir and the latter, though smaller, riskier and dauntingly hard to produce, have rabid fans and are economically very significant. Said another way, there are commodity wines and fine wines and each has a place in the market. Near anything goes in commodity wine production and the largest amount of science is applied to them. They are also typically abstracted to lowest common denominator tastes. Commodity wines don’t typically flirt with aging because aged wines are so often an acquired taste.

But aren’t people going to get rich and isn’t it going to shake everything up and give new producers a foot hold on the market? No, because if connoisseurship isn’t dead, the laws of perfect information will suppress the price and producers practicing accelerated aging won’t make significant amounts of extra money. Likely consumers will finally figure out what aging really means to them and there will be invigorated thought and education on the topic, thus moving the market. But hell, I do drink and pour handle upon handle of commodity spirits so bring it on if you can truly deliver on the sensory values. Have fun with your razor thin margins, you’re still in commodity spirit production hell.

Aren’t we making some assumptions that more aging is always better and the product will always be more enjoyable on a sensory level? Big assumptions that are bunk! In the wine world, wines gets too old all the time or a wine is old and very much alive, but just not extraordinary. Then there are adages like there are no great wines, but only great bottles. There is so much chaos in the systems that create wines, even during the aging process, that some hook left and some hook right. Maybe accelerated aging could be called controlled aging and it would eliminate the chaos and variability? If that is true, those products will alienate all the single barrel consumers who wanted to dip their nose into chaos whether they can articulate it or not. Do they say fuck your inevitability engine! with every drop they drink or are we all just taking most of our drams for granted?

I think on the technical end, Lost Spirits inspiration for pursuing fake aging came from their second investigation which I recently took a look at and wasn’t very impressed by. One line in the paper grabbed me as significant.

We learned that the VOC range aroma compounds (primarily fruity esters) mature concentration appears to be predetermined prior to barreling.

They kind of think of aging as a two part process (though it isn’t). You have the most volatile fraction which is pretty much the distillate you put into the barrel and then you have the semi volatile fraction which comes from the wood and the chemistry gets a little more complex and even maddening. Their idea hinges on the volatile fraction just ending up in one predetermined inevitable equilibrium place while the complicated part, which is the significance of their process, is getting the semi volatile fraction where it wants to be (choosing how many years). The whole system is oversimplified and cuts out the role of the angels share though they do acknowledge that.

Davis says that’s because the Model 1 does not allow for any substantial evaporation: Put in 100 liters of white dog and you get back about 98 liters of aged spirit. Without the “angel’s share”—equating to about 50 percent evaporation in a 33 year old rum—it just doesn’t seem possible to push a spirit any further.

So there are dramatic acknowledged limitations but that doesn’t void anything, though it does remind me of when you find a wine with interesting aroma and then you taste it, and its flabby because of not having enough acidity. Its just not a total package. It doesn’t beg you to drink more, but could it be a fraction for blending? One reason I use this flabby analogy is because of the lack of angels share, I bet these spirits are flabby with an incomparable amount of total acidity relative to the spirits they are aiming at.

Lets back track before we dive into some science. The best look at aging for the layman I’ve ever seen came from a 1954 State Board of Equalization correspondence which I highlighted in a post called Barrel Aging / Rhetoric / Information Design. I was so taken by how well and concisely the paper summed up the process for a court case. So much tax money was riding on the explanation that it was whittled into a masterpiece. Is the barrel just a manufacturing aid to hold spirits that should be taxed or is it a primary ingredient in spirits making that shouldn’t be taxed? The paper provides background and makes barrel aging seem less like voodoo. In Lost Spirits white papers, they had characterized spirits aging as something that little was known about and couldn’t produce a bibliography.

For one stop shopping, lets turn to the 1980 4th edition of Technology of Wine Making which has spectacular sections on the accelerated aging of wine and the accelerated aging of spirits. This is no lost esoterica, the text is pretty much the most widely read industrial compendium on wine making (and brandy production) and has been the bible of countless producers. The chapters are excellent reviews of the literature and all end with a bibliography written by Maynard Amerine who was known to be obsessed with collecting literature and compiling bibliographies.

The funny thing about bringing up the great UC Davis bible of wine making and distilling is the the Wired article had a UC Davis professor of engineering, Greg Miller, vouch for Bryan Davis of Lost Spirits as “the real deal”. It makes me wonder if Miller read any of the Lost Spirits papers or was aware of the seminal work on distilling done at UC Davis over the years.

The most interesting thing about the chapter on the accelerated aging of wine is the comments on how techniques, developed at the repeal of prohibition to jump start the industry and more rapidly bring products to market, have become adopted, not as tricks or gimmicks or even associated with aging at all, but as absolutely standard wine making procedure across both fine and commodity wines. Examples of such techniques are early clarification, tartrate stabilization, and malo-lactic fermentation. So there is plenty of room for new ideas to be adopted in spirits production.

Other techniques widely used in wine production now, that relate more to what Lost Spirits is doing, involve the controlled micro oxidation of wine to develop more mature aromas. The techniques aren’t one size fits all and the options get rather complex requiring deep involvement and lots of experimentation to be to cohesive and harmonic with a wine’s style. Other more severe techniques like baking in the presence of oxygen (this resembles how Madeira is made) are sometimes used. Baking is not applied to 100% of the final product but rather to create blending stocks. Amerine et al. provides strong words of caution that “rapid aging cannot be applied by rule of thumb, but must be used with intelligence, skill, and care, adapting the severity of the various treatments to the product at hand.”

To give a glimpse of what’s been tried for wine over the years, lets quote a passage:

Most of the older treatments for accelerated aging involve some induced oxidation: exposure to sunlight or ultraviolet light, aeration at low temperature to allow easier oxygen absorption followed by raising the temperature to induce oxidation, use of ozone, hydrogen peroxide, catalysts, etc. Many of the treated wines have a “faded” or “over-aged” character which is unpleasent.
[…]
Singleton (1962) has reviewed physical methods of accelerated aging. Claims of success have been variable; overtreatments are invariably bad. Working with a variety of types of wine, Singleton and Draper (1963) found ultrasonic treatment in combination with various gases (air, oxygen, nitrogen, carbon dioxide, and hydrogen) tended to give a “scorched” flavor and undesirable results. Similarly, using ionizing radiation (Singleton 1963; Paunovic 1963) at sterilizing dosage produced color bleaching and off-flavors. Such exotic treatments appear to have little future unless the new flavors are considered attractive in their own right or are so restrained as to be an unidentifiable contributor to complexity. More promise is held for “dissecting” traditional aging into its component reactions and managing each for optimum results.”

So these guys experimented widely and truly knew their options to manipulate different reactions related to aging. The interesting comment here is about the creation of new flavors. Do the products of the Lost Spirit’s accelerated aging produce any new aromas? And could they be features and not flaws? I’ve mused on the philosophy of flaws many times. Nothing can be a flaw until symbolic value is attached and it becomes a regret, a missed opportunity, or a what could have been. The wine industry is grappling with this issue. They’ve eradicated so many basic flaws that now critics have no experience with them and when they’re found, they are mistaken for terroir. So when we are mimicking traditional aging, new aromas are flaws, unless we start to value them in their own right which we should never discount as a possibility.

I vividly remembered the weirdness of the section on the rapid aging of spirits and it was fun to revisit. I first read Technology of Wine Making eight years ago and I distinctly remember thinking I want to taste that! All of that! I’d pay money! The ideas are captivating and I could just imagine being a student back then and tasting your way through all the cryptically labelled bottles of Vernon Singleton’s experiments. Andrew Quady of Vya Vermouth fame was a student back then and I bet he could tell us some cool stories. (One of Quady’s student projects (1973) under distilling great, James Guymon, was cited in Amerine’s bibliography at the end of chapter.)

From the section on rapid aging:

Various mechanical, physical, and chemical procedures have been used to age brandy more rapidly. Mechanical vibration (even by long ocean transport), variable temperatures, ultrasonics, adsorption, ion exchangers, ultraviolet and infrared have been tried (Singleton 1962). Ozone, peroxide, permangranate, electrolysis and metallic and biological catalyzers have also been used.

So a lot of the same processes used for wine have also been used for spirits. We don’t exactly know what Lost Spirits is using but here are some options (though the section of the Wired articled on Prior Art casts aside a few). One thing to note is that I don’t remember any of the big modern distillation texts having any sort of similar sections on rapid aging.

No statistical data were given. The best that can be said is that some of the results have been encouraging. The economics of the treatment and unprejudiced sensory examination of the products have not always been adequately considered. Further work can profitably be done.

This is very UC Davis language. They were optimists but the were definitely rigorous scientists and didn’t fall in love with their ideas becoming biased. Some other distillation texts have no such language and sometimes you wonder if they truly every tried an idea or if it was just armchair speculation. Amerine et al. definitely sets a standard we should all aspire to.

The Soviet literature recommends using oak chips (treated with alkali or untreated) in the early aging of brandy. Oxidation of tannin substances during aging was responsible for the darkening of color. Ethanolysis of lignin and hydrolysis of hemicellulose also occurs. Ethanolysis of lignin results after oxidation in formation of aldehydes of the vanillin type.
[…]
This was considered the equivalent of 3 to 5 years’ aging in wood. Lashki (1963) found that lack of oxygen during storage slowed the rate of aging but that too much oxygen resulted in loss of bouquet and the harmonious relation between components.

The Soviet Union collapsed possibly because everybody was subjected to fake aged spirits. We see so many producers experimenting with oak chips but are they treating them to enhance the process? The part I omitted are the finer chemical parameters to use as a template. As widely used as oak chips are, I don’t think anyone in the new scene has deepened their involvement enough to treat them properly.

Heat treatment of young brandies of 20 days at 38°-40°C (100.5°-104°F) with or without oak chips (30 days) improved their sensory quality (higher volatile esters, aldehydes and furfural and less volatile higher alcohols) according to Abramov et al. (1976)

Here, heat changes the reaction kinetics and modern immersion circulators make this easy to perform on the small scale. Lately I’ve been exploring this simple enclosed heating to hasten post distillation esterification in my cocktail centric distillates. In the Wired article, it was mentioned that the Lost Spirit’s process could be used for “prototyping” but I have also developed a similar process where I simply sacrificed a portion of already aged spirit to a food dehydrator (low temp evaporation) to create a semi-volatile and non-volatile fraction of high fidelity. It works astoundingly well and is spectacularly affordable. It has already been worked into my Distiller’s Workbook.

Pro and Etienne (1959) have shown that distilled spirits produced before 1954 can be dated with reasonable accuracy from their tritium contents. After 1954 the tritium content of the atmosphere was affected by hydrogen bomb explosions. Further, it is not possible to determine accurately the age of spirits which have been diluted with post-bomb water.

Are they messing with us? We call so many hacks these days “mad scientists” and these guys were hip to tritium contents?

The most interesting ideas in Technology of Wine Making were not in the rapid aging section, but another section titled Changes During Aging. I think this is the best hint of what Lost Spirits is doing.

Dzhanpoladyan and Petrosyan (1957) believe the aging process begins with the extraction of phenolic compounds from the wood, followed by their oxidation by atmospheric oxygen to peroxides and participation of the peroxides in subsequent reactions. Lignin was shown to decrease during aging and it is considered to play an especially important role as vanillin is one of its oxidation products.

Petrosyan et al. (1976) found more free-radical products in aged brandies. Irradiation of wooden barrels with UV or γ-rays increased the oxidative reactions, enhanced maturation and gave higher free-radical products. Similar effects were found when the barrels were heated with oxygen for 12 days. Mndzhoyan et al. (1977) heat-treated the oak in an autoclave at 120°C(248°F) for 100 hours at 15 atm oxygen pressure. This reduced the cellulose and increased the lignin and aromatic aldehydes. Ethanol extracts of the treated wood were very high in aromatic aldehydes–comparable to 20 to 50-year-old brandy.

This last paragraph is my best bet of what is being done at Lost Spirits. Their reactor simply accelerates the breakdown wood into aroma compounds and an extract is prepared. The extract is married with the rest of the distillate and then esterification is taken to a new equilibrium perhaps by baking. Keep in mind these particular experiments were not conducted as a means of faking aging, but rather to study the various reactions by creating some sort of nth degree scenario that made them easier to look at. Maybe they weren’t considered for accelerated aging because expense made it nowhere near viable at the time.

I know I want to taste it, but would the results of a such a process really compare to a 20 year old rum? Could you spot the fake in a line up of real McCoys? Let’s back track to James Guymon’s classification of the changes occurring during aging:

1. Physical
a. Losses by evaporation or soaking
b. Changes due to concentration by evaporation or to dissolution of substances from the wood.
2. Chemical
a. Oxidation of original or extracted constituents.
b. Reaction between original and oxidation product or dissolved substances.

Well in the Lost Spirits process, we are already missing 1.a., the angels share, therefore critical ratios are out of wack. So there is the shell of an aged product, but none of the divine details. Van der Rohe said God is in the details. We have well intentioned stick figures, but no Vitruvian man. #GrapeDrink

When Chromatography and mass spectroscopy became more prevalent to the study of spirits, many of the papers started look at the correlation between objective counts of chemical compounds and their correlations to organoleptic assessments of sensory quality (because that is the final verdict). The researchers all threw up their hands in frustration. They are confident in their ability to count chemicals but they can’t find straight forward correlations between the compounds and quality. Phenomenology kicks their ass. Our percepts are so infiltrated by recollections and other complexities, and though we can demonstrate astounding sensitivities at times, at other times we can have terrible contrast detection abilities. There is also a nitty gritty of attention within perception where just accumulating too much acetaldehyde can start to overshadow other rare and extraordinary aromas rendering the experience flat. You’d think the ratios would be pretty easy to figure out but they’re not. They’re also subject to little understood fixative effects where one obscure ester bridges another creating a unique percept. Everything becomes wildly interdependent and modeling it eludes our current abilities. Nothing beats traditional time in the barrel and the only thing that beats that is the massive amount of experimentation and data analysis large distilleries have privately conducted to maximize traditional time in the barrel.

The only thing I couldn’t really figure out was the oak catalyzed esterification term that was thrown around in the article. I don’t think it is an accepted industry term, but rather something Lost Spirits came up with themselves, possibly because they are confused and denying oxidation as a process. I suspect it implies the oak extraction product’s ability to induce acid catalyzed esterification, which is a thing. There could also be some sort of heterogeneous catalyst like tin, but that easily gets beyond my knowledge and I don’t recall ever seeing anything like it in the beverage literature though this paper on producing perfume esters seems especially encouraging.

New-make distillate is distinguished by short-chain molecules called carboxylic esters and short-chain fatty acids. In a white dog or unaged whiskey, these have aromas that include overripe fruit and paint thinner and vinegar. Drinkable, but rarely worth savoring by the fire. Still, you need these chemicals to start with, because the interaction between these compounds and the wood in the barrel results in two processes: extraction and esterification.

Various parts of the Wired article, like the above quote, embrace over simplifications. Extraction produces no magical results without oxidation as we saw in the classification of aging changes from James Guymon. Aging is about tons of slow oxidation reactions and then further reactions from those products. The new make distillate is also not at equilibrium but rather rearranging from the time it leaves the still. The whole process isn’t a straight forward relay race you can simply run faster, its a dance with multiple partners trading partners all the time due to chaotic variables. Spirits aged differently during the Clinton administration than they did under Bush.

Lost Spirits doesn’t seem to acknowledge oxidation as a process. In the section of the Wired article titled Prior and Future Art, the work of a competitor, Terressentia, uses “ultrasound and oxygenation to purportedly induce the production of long-chain esters”, but “based on their patent, Terressentia is where we were five years ago,” says Bryan Davis. For some reason that is the only acknowledgement of oxidation in the entire article and it relates to the techniques of their competitor. Is Lost Spirits naive and not aware their process uses oxidation or are they being cagey and evasive until they can make some money off their process? Or could I be wrong in interpreting Amerine et al.’s explanations that oxidation is absolutely a paramount part of the aging process. They could also be the victim of a shoddy writer who said, “Bags of sugar are easier to come by”, regarding a distillery that makes a molasses based rum.

Did I even make any progress getting to the bottom of this?

Wired used 2,200 words, I’m guilty of using 3,900.

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I aspire to eventually examine Lost Spirits new aging technique but I thought I should start by looking at their first white paper which I read a while ago. Here is a link to their paper: Trace Carboxylic Acid and Ester Origin in Mature Spirits.

This was my conclusion but I’ll move it to the beginning: I think this paper is really cool, but sort of naive. I’ve wanted to see new distilleries start doing investigations for a while now and I hope to do more myself. The sad thing here is that it isn’t that sophisticated yet made big rounds around the internet and that shows that the spirits community just hasn’t gotten very far. I saw no intelligent comments on the paper from industry peers. Lot of cheer leaders and then lots eye rolling, but nothing constructive.

The biggest disappointment in the paper is the bibliography. It kind of shows I haven’t achieved much. They cite one source when I’ve read & wrote in this territory for years and made countless papers available and annotated & commented on all of them. I’ve tried to create a culture of openness and constructive comment that I found in so many of the giants of distillation that I’ve read. It started with Amerine then it was Valaer, and Guymon, and Willkie and now Piggot. Openess and a high tide lifts all boats is the true culture of the industry and how all the research got lost and forgotten, I don’t know.

Oak matured distilled spirits are one of the least well-understood consumer products in the world.

I would say this statement is less true than people think. This blog hosts and uncovers unending mountains of scholarly research done by the industry. Its true that few in the industry, especially the new arm of the industry, are aware of the research body and I’ve talked to distillers that have been in the business thirty years and they’ve never had the benefit of any of the papers I dig up. They just don’t understand where I got them all from. The library? Inter library loan? I simply go to the library. And then I actually read the papers.

Oak maturation, by contrast, is not well understood. Much of the information printed on the topic also contains gross factual errors and flawed assumptions. Perhaps even less well understood is the potentially important interactions of chemicals formed during the fermentation with compounds extracted from the oak.

Oak maturation is far better understood than people realize. Big players in the industry right now even do tons of private research and use very sophisticated data analysis to learn more and more about oak aging. In the spirits industry, there is a tenuous relationship between tradition and innovation and much of the research that is done is down played and sort of hidden. There are some factual errors in the older literature and you will see some researchers point this out and update ideas as methods got betters. A lot of analysis methods used all over the field of chemistry were pioneered through studying alcohol and a lot of giants of spirits chemistry like Peter Valaer, Herman Willkie, Maynard Amerine, James Guymon, and now John Piggot have made massive contributions. Piggot is my absolute favorite. I love his writing style and he seems to have the best command of both chemistry and neuroscience while others are sort of lopsided.

The last comment, about chemical compounds produced during fermentation reacting with chemical compounds extracted from the oak, probably refers to esterification reactions the paper aspires to study. There is an equilibrium amount of esters a spirit can hold. To move towards the equilibrium esters are either forming or breaking apart (into fatty acids and alcohols). Compounds extracted from the oak change the equilibrium, increasing the amount of esters a spirit can hold.

The most comprehensive study on the topic was published in the Journal of the American Chemical Society in 1908 by C. A. Crampton and L. M. Tolman. Unfortunately Crampton and Tolman lacked modern tools such as gas chromatography and mass spectroscopy making their work very incomplete.

Crampton and Tolman is an interesting paper, but its far from the most comprehensive and so much has happened since it came out. One of the my favorite papers that will have gigantic impact on new distillers is: 1968 ANALYTICAL PROFILE OF CISTERN ROOM WHISKIES Schoeneman, Robert L. and Dyer, Randolph H. J. AOAC (1967), Vol. 51, No. 5, pp. 937-987. I keep procrastinating digitizing my copy (nag me and it will happen). At the end, the paper has a great reflection on the investigations of Crampton and Tolman and where the American whiskey industry has come since then.

Maybe I should whip up a brief & incomplete bibliography to give people ideas about what is out there:
Changes in Whiskey stored for Four years (Peter Valaer 1936)
A study of Whiskey stored for four years in Plywood Barrels (1950)
Changes in Whiskey while maturing (1943)
Comparison of Scotch malt whisky maturation in oak miniature casks and american standard barrels (Piggot 1995)
Effect of cask charring on scotch whisky maturation (Piggot 1993)
Flavor components of Whiskey I (2001)
Flavor components of Whiskey II
Flavor components of Whiskey III
Foreign & Domestic Rum (Valaer 1937)
Influence of distillation system, oak wood type, and aging on composition of cider brandy in phenolic and furanic compounds.
Origins of Flavour in Whiskies and a Revised Flavor Wheel: A review (Piggot 2001)
Role of Organic Acids in Maturation of Distilled Spirits in Oak Casks (1999)
Volatile Fatty Acids in Some Brands of Whisky, Cognac and Rum (1968)
Feed stocks, fermentation, and distillation for production of heavy and light rums
Production of Heavy Rums (Arroyo)
Robert Leuté’s 1989 James Guymon lecture

I could go on and on and I’d list some of the more modern complete grad school text books on making spirits which are really impressive. Then we could also list papers on accelerated aging and why they worked or didn’t and that would give us more clues into what we’re ultimately looking for. There is a cool section on accelerated aging in the Technology Winemaking.

So its safe to say there is a lot more than the work of Crampton and Tolman in 1908. One reason we know so much about aging from the IRS chemists such as Peter Valaer is that to detect fraud in spirits, they had to know what legitimate aging looked like to find the outlying fraudsters. If you say it was aged for X years, why doesn’t it have the chemical hallmarks of a X year product? We didn’t yet say anything was an ordinary, sub par, or extraordinary product, we just counted chemicals to test a claim that is symbolic as well as sensory.

Carboxylic esters are the compounds responsible for fruit flavors found in nature. They have long been observed to form during the oak maturation of distilled spirits and are thus of great interest to us as spirits makers. Carboxylic esters are formed when an alcohol chemically bonds to a carboxylic acid.

Keep in mind esters form as well as split apart. The equilibrium of what can be held together changes as the other variable change due to aging. Besides during aging, esters and their precursor caboxylic acids are inherited from the fruit with some fruit having more than others. Esters and carboxylic acids (also often referred to as fatty acids) are formed during fermentation. Esters also form in the still, especially a pot still because of the longer time under heat seen relative to the typical operation of a column still.

So you can track these aroma compounds and their precursors at every stage of the process and research has done that. And don’t forget, some are more noble than others. Some of the fatty acid ester precursors even get removed during chill filtration of superbly aged spirits so it isn’t all that simple. It would be great to learn more about what gets removed and why they didn’t form esters.

While it is well known that esters form during oak maturation, what is not known is the degree to which precursor carboxylic acids originate from the charring/toasting of the barrel vs from bacteria and yeast in the fermentation and which ones originate where.

This is known and has been the subject of a lot of investigation. This is asking, is there carboxylic acids in the wood? I would say not as significantly as the other steps of the process. Keep in mind, we use new oak, second use, and third use. And none is more superior, each has its purpose, especially the latter in rum aging. So by the third use, tannin is reduced, vanilla like compounds are reduced, and the barrel which can be re-charred is mostly a vessel to soak up congeners (in the char) as well as a vessel with special porosity to get just the right effects of the angels share and slow oxidative changes. Equilibrium has so many variables and you don’t want to change one too fast. The slowness of barrel aging means little reactions keep marching around in a circle and we can catch it at its most beautiful point before things run amok.

In order to study them in more detail 5 commercially available rum samples were subjected to direct inject mass spectroscopy and compared. The instrument also picked up peaks of some relevant aldehydes with similar volatility values.

The problem with direct inject mass spectroscopy is that the reading gives tons of biases. Lots of stuff overlaps and it takes serious computer modeling to be able to untangle a reading. When the industry uses inline monitoring of product with spectroscopy (which feeds them massive amount of data), they can only untangle the reading into something meaningful because have done tons of leg work with chromatography to create robust models to apply to the spectroscopy.

I’m not qualified to say much. I know how to read the results but not to operate the equipment and I know a significant amount of their limitations from reading so much. Using advanced analysis techniques for spirits differs from other fields like biology. Spirits often require exotic sample preparation techniques because all the ethanol or sugar biases the results. If spirits are 99% ethanol & water and 1% congeners, you need to extract that 1% to get a better look with any real fidelity. Often you use serious organic solvents like hexane and dichloromethane to pull the congeners out of the ethanol and then you separate those organic solvent with a vacuum still to isolate the congeners.

I have played with hexane a lot. I wanted to see if I could explore sample preparation in a beautiful context. I tried to suck the congeners out of gins and cognacs and was going to isolate them and then add them to fernet or make a double cognac, cramming twice as much aroma inside. Well it didn’t work like I thought and became wildly expensive. I was getting to a point where I needed to explore continuous liquid-liquid extraction which required expensive glassware (and then I pretty much ran out of money).

NOTE: Traditionally ethyl acetate has been the most extensively monitored carboxylic ester, as it is the easiest to detect due to concentration. It almost certainly originates in the oak, because it is known to increase with every year that a spirit ages without stopping. However, ethyl acetate has a very high aroma detection threshold and thus has less impact on flavor than other trace carboxylic esters we are interested in studying in this paper.

Even a hundred years ago they were aware of the differences in esters and their contributing qualities. Ethyl acetate is not exactly the most monitored, but because esters used to be counted with titration, which can count esters, but not differentiate them, the number of esters was expressed as ethyl acetate which is a chemistry counting convention. Ethyl acetate is the most common ester by far and the most basic in its building blocks. Sometimes carboxylic acids are referred to as long chain or short chain. Acetic acid is the shortest chain and most basic. When winemakers count total acids with titration, they do something similar, counting everything as tartaric even though other types of acids are present. Simplifying total acidity is enough to give them useful data to base decisions on. It is not fair to say that ethyl acetate has less impact on flavor because there is so much of it relative to other esters.

There might be ethyl acetate in the oak, but that is not as significant as the other sources. Robert Léauté’s 1989 James Guymon lecture (page 11) gives an easy to understand chart examining the esters found in cognac wines after fermentation. Ethyl acetate is the most common ester out numbering other esters by giant magnitudes except ethyl laurate. Léauté even gives the advice that fermentation temperatures are carried out at a specific temperature so that some of this ethyl acetate evaporates and then eventually much of it will be removed from the hearts fraction with the heads cut. Léauté’s lecture is the greatest concise primer on distillation ever written.

One reason ethyl acetate can form as spirits age is due to the oxidation of ethanol to form acetic acid and ultimately linking up with an ethanol to become ethyl acetate. There is even some acetaldehyde in there as an intermediate step of the oxidation process. This is all governed by shifting equilibriums. Distillation doesn’t produce something that comes out of the still at equilibrium. Its more like all shaken up and therefore rearranges pretty quickly. Besides the porous nature of oak, which facilitates oxidation, compounds extracted from oak which lower the pH can be a catalyst for reactions and influence the various equilibriums.

The fact that the aging and distillation of these two products was so similar appears to suggest that the key difference originates in the fermentation (likely yeast strain choice).

This quote refers to two chromatograms shown in the paper. Yeast strain choice is a thing, but there are also many other variables that define spirits.

It is possible that a variation in charing of the wood could have provided the difference, or perhaps a subtle difference in distillation protocol. The warehouse climates are assumed to be highly similar so that was likely not a factor. Also idiosyncratic barrels could be ruled out as both products are blends of hundreds of casks.

These ideas are just the tip of the iceberg of potential production differences.

The fact that the fermentation and distillation of these two products was so similar yet the sample on the left is nearly twice the age of the product on the right, and is nearly identical in VOC fingerprint appears to suggest that by the 7-8th year of oak aging all of the volatile range carboxylic ester formation is complete. This would strongly suggest that the carboxylic acid precursors for these pungent trace esters originate entirely in the fermentation and are not derived from the oak. If the precursor acids were derived from the oak we would expect to see far higher peaks in the 15 year rum.

This quote refers to another set of chromatograms. I would say based on every paper I’ve ever read, that desirable ester precursors for rum come from the fermentation. And remember, post distillation esterification is a thing, but esters are also born in the still and when you have the right stuff in your fermentation that is why you go to the expense of a pot still distillation with a long time under heat if you want to make a heavy product. And don’t forget, a column still can be operated to achieve a lot of the same objectives.

The fact that the fermentation and distillation of these two products was so similar yet the sample on the left is over 3x the age of the sample on the right appears to further confirm the suspicion that the carboxylic ester formation is complete by 7-8 years of aging. It also appears to soundly confirm that the trace carboxylic ester profile of a mature rum are essentially predetermined prior to aging. Though it may take as many as 7 years to complete the process – further aging cannot form additional trace carboxylic esters beyond the level of precursors available from in the white spirit.

So you can’t put a light rum in a barrel for 25 years and get a heavy rum.

Given the prior observations comparing and contrasting various column distilled rums a final comparison was made against a 33 year aged pot distilled rum. As was expected the pot distilled rum showed significantly higher peaks for every target ester owing to the fact that the pot still provides much less efficient separation and allows far more of the chemical composition of the fermentation to pass into the final spirit. This observation appears to confirm that the trace ester density is not only predetermined prior to the spirit entering the cask but that the distillation cuts and level of rectification has a massive effect on the final character of the aged spirit. Given the conventional wisdom that aging can “fix” certain off notes in spirits, this is not surprising as many off notes are in fact carboxylic acids that have not yet been esterified during the aging process.

So many variables can come into play here, but one of the major ones again is time under heat. The cuts can be similar and you can distill with a column still at a very low proof but the time under heat in the boiler is going to be much shorter creating less time for acid catalyzed esterification in the still.

Trace carboxylic esters (excluding ethyl acetate) in mature distilled spirits are responsible for the fruit flavors often seen in desirable products. While it is true that the spirit must be aged in oak to increase ester density and convert off notes from carboxylic acids to desirable esters, it was found that their peak concentration is limited by precursor carboxylic acids generated in the fermentation.

One this this misses is the fixative role of ethyl acetate described by Robert Léauté. You want ethyl acetate as close to the recognition threshold as possible without going over. When you go over the recognition threshold, ethyl acetate will smell like nail polish remover, but when below (but well above the absolute threshold), ethyl acetate will be a bridge for the other aromas. Without ethyl acetate to bridge aromas, they will be perceived as disparate and possibly dissonant. The fixative term is used in many different ways but here it brings aromas together (spatially in the mind) to create unique and extraordinary percepts. A large part of distilling and blending is managing ethyl acetate.

It was further observed that pot stills are far better at capturing precursor acids from the fermentation than column stills. However, I would expect column stills designed for lower rectification as is common in Armagnac or Martinique produce to results more closely related to those shown for the pot still rum.

Not every distillery owns a pot still, but precursor potential is a big part of choosing to operate one or not and don’t forget about time under heat. One of the reasons California never had a lot of pot distilled brandy was that their wines were too low in acid to produce enough precursors to justify the added expensive of more time under heat that a pot still generates.

To achieve Lost Spirits’s goals of making the most heavy, robust, rich rum possible, it is apparent that a pot still is ideal. The observations also show that special attention must be paid to the bacteria and yeast strain choices in fermentation. Fermentations could be engineered to generate higher concentrations of favorable precursors. This optimized fermentation coupled with a pot distillation could then generate white spirits more suited to gain substantial flavor density through esterification during the aging process.

Awesome. One of my goals when I started exploring distillation was to explain all the nitty gritty operational differences of still operation which was sort of mystified so that producers could have enough clarity to start working backwards into deeper involvement with other aspects of production like fermentation and cultivation of raw materials. Still operation was just getting too much fetishization and I couldn’t find much intelligent written about it.

Attention will have to be paid to yeast of course, but don’t forget pH, fermentation temperature, the recycling of fractions, the use of dunder, and finally the quality of the molasses.

Of course esterification of trace carboxylic acids (excluding ethyl acetate) is only one component of the aging process. Oak extractives and phenolic compound reactions must be addressed with the same vigor to gain a full picture of the maturation process. The ethyl acetate formation must also be studied in the context of these observations as acetic acid extraction from the oak is likely influencing the equilibrium of the aging spirit (as a buffer solution) in an important way.

And luckily lots of papers address all these concerns. I think that acetic acid extraction from oak won’t be found like the authors think. It will come from other places like the ethanol itself or most definitely in the fermentation.

If you want to learn about any of these concept without having to run a large scale rum distillery, don’t forget to explore my distiller’s workbook. Some of the exercises like the cocoa bourbon or the marmite rye help to explain and explore acid catalyzed esterification in the still. I also did some other unpublished experiments like distilling walnut nut oil or a Sauternes that dramatically illustrate post distillation esterification and the march to equilibrium. After distillation, the nut oil distillate does not organoleptically resemble walnut, but then many months later, a dramatic change occurs and it does. Distilling the Sauternes reveals how much acetaldehyde and plain acetic acid it contains (hides!) and immediately upon distillation it smells horrific and undrinkable. Many months later the distillate mellows and comes to a new equilibrium. It does not end up delicious but it does end up different, illustrating relevant concepts.