Flavour Components of Whiskey. I. Distribution and Recovery of Compounds by Fractional Vacuum Distillation
Flavour Components of Whiskey. II. Aging Changes in the High-Volatility Fraction
Flavour Components of Whiskey. III. Aging Changes in the Low-Volatility Fraction
This novel experiment explores how different components of a whiskey change over time in a barrel. The novel part is how they track the components which relates to experiments I have done in the past and my own fake aging technique.
The first part of the paper details how a whiskey can be separated into different segments via fractional vacuum distillation. What they perform is quite complex to execute and certainly beyond me, but actually possible with off the shelf components as they prove. They cut a whiskey into five distinct fractions while in my own greatly simplified experiments, I cut whiskeys only in half.
What is cool about this set of papers is that it validates my intuition that the bottom half, the least volatile fraction, represents a significant portion of what barrel aging contributes. I had taken this aqueous fraction in the past and added it to other high proof spirits to synthesize aging which can be just plain fun to explore or possibly a predictive tool for a distiller. I had also cut spirits in half down the lines of volatility, manipulated the fractions independently then rejoined the two fractions which this paper somewhat validates as representative with their own organoleptic experimentation though they did control for far more variables than I did.
The second paper, which looks at the most volatile fraction is a good read which I don’t have the time to completely detail. The most notable part of it for me, which I need to learn significantly more about, is this tidbit:
In the case of wine, acetates are considered more important than ethyl esters of fatty acids for intensity and quality of aroma (van der Merwe & van Wyk, 1981). The same is likely for whiskey because of the low sensory odour threshold values of these compounds (Salo, 1970).
I can’t speak in any real depth about acetates, but I think they form through more complicated aging reactions rather than relatively easier to understand processes like acid catalyzed esterification of ethyl esters in the still.
[Gary points out that acetates are simply the anions (negatively charged ion) of the acids we know so nothing too exotic. I definitely did not understand too much chemistry when I wrote this years ago.]
Part three is particularly cool because to some degree you can play along easily since they are concerned with aroma compounds in the aqueous solution. They isolate their aqueous solution with a complicated fractional vacuum distillation procedure but ball park approximations can be gotten by simply putting a whiskey in a food dehydrator until the alcohol is removed.
The paper starts to get really complex and starts offering new ideas for authenticating spirits based on ratios of congeners. Page 5 of part III has some major errors in the scanning that removes part of the page but its in a section that is very technical. Eventually they isolate a few congeners (phenolic esters) they believe are crucial to mature character and then syntheticaly add them to younger spirits to organoleptically test with a tasting panel whether they increase the perception of maturity. The relationship of their contribution is not straight forward but eventually, at high concentrations, they do increase the perception of maturity.
One of the big takeaways here is how we might design educational tasting experiences for spirit tasting rooms and educational seminars. These papers validate my idea that spirits can be cut into pieces along the lines of volatility and then reconstituted in various ways. The fractions can also participate in mash-ups and when abstracted in different ways, teach us new things about perceptual thresholds which I’ve only explored in the past at the lowest level.
Also, check out the bibliographies. This team references older material I’ve never seen, possibly because they own unique collections. One of their books is a rare gem I’m now trying to acquire, bet you can’t spot it!
3 thoughts on “The Flavour Components of Whiskey in Three Acts”
The acetates – are the acids – acetic acid (acetate = the anion of the acid). 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.)
Great to hear from you Gary. This acetic acid buildup which leads to an ethyl acetate increase is quite fascinating. Your hint about the source may give the starting point to answering a lot of questions about maturation and spirits like high-ether rums that have massive surpluses of volatile acids and ethyl acetate.
When Arroyo designed spirits that were quick to mature, did they get a high start because they entered the barrel with a head start of low pH from noble volatile acids?
What can we expect when a spirit with surplus ethyl acetate (like a high-ether/grand arome rum is put in a barrel? Will it’s ethyl acetate ever go down via the angels share or does it always increase similarly to a bourbon before it eventually plateaus?