A great paper, Character in Pot Still Whisky Part II, from Hastie and Dick in 1928 which provides a lot of information on furfural and some real gems on the state of distillation at the time.
The main section is sort of technical and won’t interest the non distilling connoisseur but the comment section at the end is full of wonderful gems that explain the state of the industry in 1928. I hope to find as many of these papers with comment sections as I can.
“There was one thing Mr. Hastie had remarked upon early in the paper which provoked a smile, and that was with regard to the cleaning of the stills. He himself could give a case in point in which the absence of cleaning of the stills might have a very considerable influence on the character of the whiskey produced. He was in a certain distillery for about a week some years ago and a very conscientious still-man was in charge. At the end of the period the whisky was not what was desired, and one of the proprietors told him that the whisky tasted in a manner which they had been trying to prevent for the previous five years. When the still-man was cross-examined it turned out that he had been rather too energetic in his cleaning, and had cleaned beyond the point to which he should have gone in order to maintain the characteristic flavour of the particular whisky.” The impact of copper on distillation is very complex and apparently copper can be too clean. One other paper concerning copper more specifically describes their priming of their experimental still before they studied what effect copper had on the distillate versus stainless. So far I haven’t come across any hard and fast rules of thumb. I suspect over cleaning might be a problem for new distilleries because they are often sharing one still among many products that they make such as a vodka, whisky, and a gin.
“He decides to discontinue the collection of “foreshot” and to commence collecting potable whisky when the distillate no longer turns blue and clouded when water is added in time-honoured fashion. He later decides to cease collecting potable spirit and to proceed to collect the third and final fraction by observing the alcoholic strength of the distillate, experience telling him at which particular strength to affect the change over for the particular plant with which his is concerned.” I had never heard this about a blue distillate identifying a heads cut. It makes sense because that is when corrosive fatty acids are at their highest but I wonder how this rule of thumb overlaps with approaches now based on mass-spec and empirical taste thresholds.
“It was a pity that samples could not be taken during the actual distillation, but he was afraid that the easy going ways of the South of France would not be allowed in this country.” This gets revisited later but excise rules were so strict that there were no provisions to legally collect samples for research.
“It seemed, however, that whisky was produced more by tradition than by science, and a man who had a distillery which could produce a full whisky had a valuable asset.” I suspect the audience is mostly full of brewers and their science was much further ahead of distilleries. Success back then of a distillery seems to be mostly by chance.
“Mr. Hastie had suggested that furfural was largely produced by caramelization and he
wondered if it were possible to remove the rousers from the stills. Years ago all the
coppers at his Chiswick brewery were fitted with the rather alarming chain rousers,
which were practically impossible to to keep clean and needed constant renewal.
Contrary to all the traditions of the place at that time, he had insisted on removing
the rousers, and the coppers were much easier to clean in that they were unhampered by
the rousers, and except that the bottoms of the coppers showed a certain amount of
caramelization, the rousers were never missed. Possibly the little extra
caramelization which was obtained in this way would produce more furfural.” The “he” here is not Hastie but another commentor with brewery experience. Rousers basically stir the pot to prevent burning. They are hard to clean and I guess this brewer thought he could do without them.
“He seemed rather to have given the impression that distillers never cleaned their plant. He should, perhaps, not have said that the stills were never cleaned, but that it was not the custom to remove the deposit which was automatically left in the worm and in the lyne arm by the action of distillation. It was that, rather than that the distilleries were not cleaned, because the fermenting and other vessels were scrupulously clean.” So distilleries were clean, but deposits were just left inside the stills because it was known to effect flavor. No one knew the science of this back then and it still isn’t well understood.
“A curious thing was that certain countries which import whiskies in large quantities now insist upon a signed analysis by and independent analyst showing that the particular whisky imported contains a certain percentage of furfural, and if this whisky does not show, on analysis, the prescribed proportion of furfural, it is rejected.” Peter Valaer, the IRS chemist, touched upon this and furfural content implied the methods of production and whether a spirit was cut down or not. Genuine pot still whisky, which will have more furfural than something like patent still whisky, is worth more because it is typically uncompromising and gets a longer time under heat which is expensive. Stocks of pot still whiskys were often bought to be blended.
“The yeast used by distillers was mentioned by Mr. Reavenall who stated that distillers did not seem to care what sort of yeast was used. The fact was, however, that Mr. Reavenall probably knew more about distillers’ yeast than the distillers themselves, because they bought their supplies from brewers and had to take what they could get. So far as his own particular process was concerned it did not matter where the yeasts came from so long as it was good, and sound and clean. There was no question of a pot distillery requiring anything in the way of a pure culture. As a matter of fact, better results seemed to be obtained by taking a mixture of yeasts obtained from different sources rather than from one source only, although why that was so he did not know.” I’ve heard only a little of the importance of distillery yeast and have wondered what new American distilleries were using. I wonder if Bourbon producers hype the importance of their yeast strains to create almost false exclusivity or if they have actually experimented widely and truly know the differences.
“He also agreed with Mr. Reavenall as to the annoying Excise restriction. The fact was that the distillery was hardly controlled by the distilling firm. Everything must be done in accordance with the Excise regulations, and as an example of the difficulties, he mentioned that he had once desired to take samples every quarter of an hour from a still during a four hours’ operation, in order to examine the samples, but although he tried every possible way to get permission they would not allow him to take 20 cc. samples at quarter of an hour intervals throughout the run of the still.” Really fascinating is how the excise restriction shaped the spirits industry and caused them to lag behind breweries in terms of a scientific understanding of their craft. I wonder though if it ended up being a positive and preserved traditions that are more fragile that people think.
“The question of fire heating versus steam heating was of importance in connection with pot still distilling, and it had been found that the character of the whisky was frequently detrimentally affected by reverting to heating the wash still wit a steam coil, where it had previously been heated by an open fire. They were not prepared to explain why that was so. The would not say that it made the whiskey worse, but that conservatism of the distillers was such that if there was an alteration of any sort in character they would want to go back to where they were originally.” Really interesting, direct fired pot stills are thought to produce a more complex product and that idea persists today. I remember coming across new literature that shows other reactions happening due to encountering super heated hot spots other than the production of furfural. I suspect that the distilleries were stodgy because they were trying to scale up, like increase production 10x, and, true they had new equipment options, but they want to keep their product as consistent as possible even thought it was in new vats and passing through new stills. They new their character was valuable but they didn’t now exactly how they got it.
“As to the removal of rousers from a still, if that were done, it would be impossible to carry on at all because the burning and charring that would go on in the still would be so excessive that the whisky would actually taste not only of furfural but of burning. In the case of the brewer the wort was put into the copper without any yeast, etc., but the distiller was putting into the still a liquid which by comparison, was almost a semi-solid. It was carrying suspended yeast and other matters which came from the mash tun.” […] “therefore it would not be feasible to remove the rousers.” Here is a look at the rousers (stirrers) from the distillers prospective instead of the brewers prospective seen above. If agitation by the rousers is so important, what I wonder is what did the distillates of tiny five gallon farm stills taste like if they had no rouser. Were the farmers straining their wash or how else were they tackling the problem?
This chart from the paper, which you unfortunately have to enlarge by clicking on it, has furfural statistics for a variety of very interesting spirits. I cannot interpret the data but it does point to new authors: Goot, Heron, Fernbac, Schidrowitz & Yeed.