The Application of Chemistry to Pot Still Distillation by S.H. Hastie, O.B.E., B.Sc.
This is another newly digitized paper accessed from the Wiley Online Library.
In this paper from 1925 Hastie kicks off the systematic exploration of aroma/congener-centric pot still operation. This work is unique because Hastie is particularly smart and presents the paper in front of very illustrious people yet somehow does not make it into bibliographies that follow. Maynard Amerine did not reference Hastie in the 1941 Commercial Production of Brandies, Peter Valaer never referenced Hastie in any of the IRS papers, and Roseworthy Agricultural College never referenced Hastie in the decades to follow where they conducted similar work even though they were aware of Joseph Nettleton’s works.
The paper is not specifically useful to a new distiller but it does set the scene in the history of modern distillation and explains what was known and unkown at the time as well as implies how much control and consistency distillers had over their process.
What is particularly interesting to me is how advanced brewing was relative to distillation. So much science was already applied to malting and brewing but science hadn’t even explained the effect on character of running the pot still fast or slow. Art had produced many good rules of thumb but science had not explained them. Joseph Nettleton’s works predates Hastie’s and because of these giant gaps in knowledge that Hastie identifies, Nettleton’s tomes come across as basically just a treatise on brewing for distillers (not that that isn’t important!). Whiskys back then were probably damn good as proven by the recently analyzed Mackinlay that once belonged to Ernest Shackleton, but they still had one foot in the dark.
Hastie is very tactful and pragmatic when he lays out his plan for advancing distillation. He carefully fragments the process so analysis can be conducted at every step of the process instead of just with the end result. That way if something goes wrong it is actually possible to pin point the cause and correct it which he acknowledges is difficult is these stodgy, conservative operations. I suspect a lot of the new American distilleries running on no sleep and shoe string budgets do not conduct much analysis or are even aware of what is possible. If that is the case, these new distillers will greatly benefit from brushing up on Hastie and Nettleton. Analysis currently is so advanced and can be cross referenced against so much great data that the team led by the Scotch Whisky Research Institute was even able to identify the peat source of a hundred year old whisky sample.
Few people read the original papers so let me extract and discuss some choice quotes. The chemistry at the end of this paper gets pretty dense and I suspect Hastie errors a bit so I will try to compare Hastie’s work to that of Roseworthy Agricultural College and even the most current explanations as best I can.
We should probably first begin at the end:
“If I should have succeeded in arousing interest in this complicated problem sufficiently to attract any additional workers to this field of investigation, then I will be more than satisfied.”
“Subsequent to the war, however, science has forced itself upon the attention of the conservative distiller, and efforts are now being made to apply laboratory control to pot still distillation.” It is strange here how the war is credited as a catalyst for advancement. More than a decade later, war is credited again as steering W.O. Graham into exploring distillation for his thesis.
“Perhaps at this time of day it is not necessary to point out that a scientist must not be expected to enter a distillery and after a few months effect fundamental changes, for nothing short of a magic wand will operate in this way, and fundamental results arrived at thus rapidly, are in the light of experience in other directions, very likely to prove misleading.” This is really interesting because so much great work was conducted at Roseworthy on pot still operation and many of its graduates entered the industry but the Australian distilling industry was barely changed. Patience and tact might be of the utmost importance in the distilling industry.
“In a word, if we are to advance at all, the pioneer work must be carried out by technical men with scientific training in biology, chemistry and physics, with, and this is of the first importance, practical connection with and knowledge of the daily operations of the distillery.” And here we reach the limitations of any advice I can give anyone. I’ve learned a ton about distillation but I certainly have not operated a distillery and have no clue how my ideas can scale to the day to day of hundreds of gallons of this and that. I’ve heard so many similar anecdotes from the wine industry. Lots of kids graduate from oenology school but they can’t take apart, repair and fix the pumps that move the wine around.
“This state of affairs resulted from a very superficial knowledge of a very complex and conservative rule-of-thumb series of processes, of the precise workings of which the general information was, and still is, very meagre.” Hastie starts to make his case for science and analysis by examining what happens when a certain amount of grain produces a less than expected yield. Previously it was pass the buck and the blame game and distillery operations were not well fragmented or systematized to identify where the problem started.
“Considered as a rule-of-thumb process without guarantees of yield, the process is very simple, but considered as a problem in the production of full yields of a definitely uniform product the subject bristles with difficulties of the most complex kind.” Cooking is slowly being elaborated in a similar way these days with the advent of temperature controlled cooking and baking scale style recipes popularized by Modernist Cuisine. I’ve talked about this in the past with classic cocktails where recipes go from dynamic towards static.
“Quality and character are the prime essentials of the business, and all that I may say as to the value of control is to be taken subject to the proviso that this control is of economic value, and where it has affected existing character it has improved it, and has certainly not proved detrimental.” This relates to my notion of involvement. I think people thought character was the product of a lot of chaos and mystery. Things were made with a low degree of involvement so the magic could happen by itself. Being too conscientious risked stripping the magic away. If something could be more efficient, bureaucratics would push it that way to a point which compromised character. But this was a lot of short sighted thinking. Control and systematic study could help eliminate flaws, regrets, missed opportunities and ordinary aroma thus cultivating extraordinary, singular character, terroir.
Hastie goes on to subdivide the production of distilling material into malting, mashing, and fermentation where maximum theoretical yields are calculated for each segment to isolate problems. “We thus ascend from art to science.”
Hastie starts to explain the analysis of the fragmented processes which I think was well adopted by brewers but not yet by distillers. Examine barley and determine starch percentage and germinative capacity. Assess nitrogen percentage. Kiln barley to assess moisture content using a moisture standard of 3 per cent for extract obtained. Grist is evaluated because malt is subject to change with storage. During fermentation gravity is examined to be compared against gravities for ferementation completion.
Control of the yeast supplies is where things get really interesting to me.
“Hitherto the scientific care of yeast both as to storage and control in pot still distillery work simply has not existed.”
Previously I had no idea how distillers were getting their yeast. I thought they must have proprietary supplies not related to beer brewing. I suspect American whisky producers had all the same practices though I’ve never read anything to confirm it.
“As soon as the brewer has finished skimming and pressing, the yeast surplus is dumped into the general sump which is the distiller’s source of supply, from there it is forwarded (in casks or pressed in sacks) by rail and to the Western Isles by cargo steamer. It is frequently on deck in the heat of the sun, uncovered, it is collected at leisure and stored in the distillery yard regardless of temperature or anything else, and is finally drained off in buckets through a cock in the cask, the mouth of which is filthy as a rule with dried yeast, etc., from previous buckets. It is then tipped into the wash back to ferment the wort and is by this time a mixture of doubtful cleanliness, of very uncertain vitality, and certainly always a seething mass of organisms of every description. Truly a picture black enough to make Pasteur, the scientific father of our allied industries turn in his grave.” Wow, very surprising.
“There is no doubt that the yeast used is frequently blamed for defective fermentation, when the wort is the real determining factor, and so long as worts are prepared, may I say scientifically, blindfold, the distiller cannot definitely say whether the yeast or the wort is the cause of unsatisfactory results, but by controlling each of these factors he may strengthen his position enormously when complaints have to be made to the provider of his yeast.” I think that these days the yeast companies are so good that we almost do not have yeast problems.
“In the application of the system, graphs are plotted of efficiency coefficients which are kept throughout the season, and afford immediate comparisons of various distillery productions in all departments of process on a basis strictly comparable, and independent of the nature or quality of the barley employed. Distillers are prone to compare the produce of different distilleries, although the materials may vary so much that such a comparison is unfair to the operative distiller and quite worthless.”
“…control is the desirable jumping off point and must precede research. Control must come first and be complete and research must follow as the outcome of control.” I wonder how Hastie would feel about new distilleries. Do they have enough control and involvement to justify new explorations and attempts to be differentiated in the market place. Can organoleptic analysis via tasting panels be counted on for control?
And now we to Hastie’s research ideas some of which are really interesting:
“The mashing process. The question of extra yield.”
“there is the question of treatment of mash and mashing water with inorganic salts. Nettleton in his book on distilling states that 20-40 grains per gallon on salts such as NaCl or CaCl2 will enhance the diastic power and increase the amount of protein matter dissolved in mashing.” Hastie goes on a little more and I am definitely in territory I know very little about. I’ve learned quite a bit about operating a still, and of fruit based wine making but I know comparatively little about brewing. I was under the impression that NaCl seriously inhibited yeasts but it would be interesting to see how these amounts translate to g/L and therefore how much of an interesting water source could be used such as ocean water to also add organic material as well.
“From further work carried out on this question and not recorded here, as being still in progress, the opinion has been formed that the hydrogen ion concentration of the mash water and mash materials was the real factor operating in these experiments and in those of Nettleton, as adjustments of the Hydrogen ion concentrations of the water taking into account the mashing materials has a greater and more definite effect upon the yields than the addition of salts alone, and further the effect of these additions is found to be largely due to their influence upon the pH of the mash, and is, in fact, an inefficient “trial and error” method of adjusting the pH. The adjustment of the pH of pot still distillery mashes and worts is of the utmost importance to distillers and is at present the subject of investigation, but it is regretted that further details cannot be set down here meantime.” Super interesting! What I think they are arriving at here is the sour mash process. The pH is adjusted not just for microbiological stability but also for yield, and from other papers I suspect as a catalyst for esterification in the still. I was under the impression that Scotch whisky distillers did not exactly sour mash but that might not be the case or maybe they just adjust it by different means. What is also interesting is about the same time in Australia, Alan Hickinbotham of Roseworthy Agricultural College was revealing the significance of pH to the stability of wines. Prior, something like 20% of wines were sent to distilleries because they were essentially spoiled but after acid additions were made to adjust pH, that number went down to 3% and still wine product increased very significantly.
“It must be remembered, however that the success of the treatment of the mash is determined not by the water composition alone, although this is of importance, but to a much greater extent by the pH of the mash as influenced by the malt used.”
Hastie acknowledges skipping fermentation in the paper because he wants to focus on the operation of the pot still.
“When a definite scientific method of control has been arrived at, then attention may be turned to the origin of the substances stamping the character on spirit, but so long as the distiller is in the dark as to the precise effect of varying the distillation process with a given fermented wash, it is premature to enquire into the origin of the character producing impurities in the wash.” Hastie starts to propose working backwards.
“That is to say, we must deal with the second and final distillation first, wherein separation and interaction of substances takes place, before we are in a position to deal with the primary distillation where separation and interaction of substances also takes place, but where in addition new substances are actually produced not previously present in the wash.” Hastie sees the second distillation simpler than the first. A lot of magic happens in the first distillation and it is probably not fair to relegate it to a “stripping run”.
“In this way the control of the selection of the different desirable materials from the wash, and the exclusion of the undesirable, must be definitely settled, and then the origin and nature of the substances can be tackled.”
“To digress for a moment in explanation of what follows, it appears to be the case that after the Royal Commission on whisky had given its findings the tendency was to attempt to eliminate partially or wholly many of those impurities from pot still whisky which constitute its commercial asset and as the amounts and nature of these impurities are of first importance, the endeavour of the distiller is now to attempt to retain definite proportions of them in his whisky where such is already in active demand, or to attempt to incorporate the desirable and eliminate the undesirable, where the existing demand for his particular product is small.” I wonder if the popular press created a demand for lighter spirits once they had namable compounds to write about and falsely implicate in hangovers. David Wondrich could probably give us some nice background on this idea. Hastie goes on to say that whiskys with undesirable character could be stripped of it and used for blending with other whisky of more desirable character.
About congeners: “They are doubtless largely derived from the peats used in drying the malt and also found in the water which in the large majority of cases (in Highland whiskies) drains through peaty soil.” This paper pre-dates Hastie’s other paper where he spends more time on water.
“We will therefore start with the product of the first distillation that is, the low wines which in practice is normally collected and mixed with the foreshot and feints, that is, the first and last runnings from the second and final distillation of the previous period.” Here we see acknowledgement of the recycling of fractions. The Roseworthy papers explain a lot about recycling because it was not common practice in Australia despite being integral to Cognac production. It is also super important to realize that whisky is the product of interlocking batches.
Hastie presents a chart that gives some numbers for the composition of low wines + feints + foreshots (volatile acids, esters, higher alcohols, aldehydes, furfural).
“[…] in addition to which a small proportion of other very important character giving bodies are present of which practically nothing definite is known beyond their undoubted existence, […]” He realizes due to analysis constraints he is not working with a complete picture.
“The function of the second distillation therefore is to select primarily, in the whisky or second fraction an alcoholic distillate containing the above, and to exclude from this fraction by collection in the foreshot and feints and rejection via the spent lees, the undesired balance of impurities.”
Hastie presents more great data sets. One particularly cool data set looks at the second distillation (only via laboratory still) and shows the accumulation or trailing off of every major congener class over the course of 19 fractions. We should probably compare Hastie’s data against the brilliant charts of Robert Léauté’s 1989 James Guymon Lecture.
“[…] general uncertainty of the distillation as a process of separation.” All these things are being thrown at you at different rates and you have to catch them. There are lots of moving parts.
Hastie presents another data set of 80 fractions taken at 15 minute intervals from an actual spirit run in the distillery. The previous data set was only from a laboratory setup. Getting real world data is a remarkable feat back then because of excise restrictions on sampling. Esters do some very erratic things in his data set. He notes that laboratory results and real world results differ.
“One of the obvious methods in practice by which a given character may be altered always presupposing a definite low wines and feints and foreshot mixture is by collecting less foreshot or more foreshot, less feints or more feints, etc.”
Hastie spends some time explaining what happens when you enlarge or contract the cuts but then notes that those options are obviously limited and other methods need to be sought out for modifying character (changing starting proofs by altering recycling, altering time under heat, altering lyne arm to effect subtle reflux rate).
“One can readily understand that any factor tending to greater or less rectifying effect of the apparatus will at once alter the character. Such factors are increasing the height or diameter of the still neck, and inclining the lyne arm; and the use of plant designed to partially condense the spirit and so return a proportion to the still will have similar effect.” The very last part here I think refers to what is sometimes called a brandy ball. It isn’t exactly a reflux column but rather just a simple way to add more reflux to a pot still. Usage was described in the Roseworthy papers but I haven’t seen one described anywhere else don’t think any producers currently use them.
“The speed at which the distillate is driven off from the still will also have its mechanical effect on the product. As an instance of the effect of one of these factors a few tests of runs of laboratory still using the types of head and lyne arm detailed are given to show clearly how one of the variable impurities of the character producing substances, namely acid, actually reaching the whisky is varied with different apparatus.” The speed has a two-fold effect. Firstly changing the time under heat, by changing the speed, varies congeners creation in the still and secondly increasing the speed challenges the natural reflux of the still head. Explanations for these phenomenons where hard to come across but were explored in the Roseworthy projects. A pot still has more reflux options than you’d think and besides the rate of distillation, changes to the lyne arm such as angle or length can change alcohol content of distillate and thus congener distribution markedly and this was again explored in simple experiments at Roseworthy. Hastie provides drawings of different laboratory lyne arm options and shows a chart that illustrates how each option varies in volatile acids collected. I think his chart could be set up better. The options with the least amount of reflux collect the most volatile fatty acids. The volatility of these fatty acids, it must be remembered, is a function of both their boiling point and relative miscibility in water/ethanol so when reflux is varied, and thus alcohol content of the distillate varied, this relative miscibility becomes a big factor in explaining volatility. My favorite better explanation of the subject comes from Amerine’s Commercial Production of Brandies.
“[…] as the impurities tending to come over in the distillate vary with the alcoholic strength of the vapour some tending to remain in the still at the higher strengths, and others tending to pass over, consequently more or less rectification will mean corresponding differences in the amounts of the different impurities actually passing into the distillate.”
“Schridrowitz (loc. cit.) pointed out that the simple distillation of low wines, etc., gave rise to changes in the amounts of the constituents in spirit with elimination of impurities via the spent lees.” Distillation on the lees was also explored at Roseworthy because it was common practice in Cognac but not Australia. It may seem counter intuitive that distillation on lees could reduce impurities such as aldehydes.
“The process of distillation of the low wines, and feints in the spirit distill is essentially a process of hydrolysis of the esters giving acids and water of oxidation of the alcohol to aldehyde, of production of esters from alcohol in presence of acid, oxidation of alcohol to acetic acid, and many other subsidiary actions no doubt.” Hastie sets out to tackle the reactions taking place in the still. I am well acquainted with the esterification reaction but the hydrolysis reaction where esters split apart is somewhat new to me, but explained particularly well by Peter Atkins in his book on chemistry, Reactions. Hastie seems to think the splitting apart of esters is more common than the formation of esters in the still, but I’m pretty sure he is incorrect.
“Apparently the distillation in the normal courses in practice increases the acids at the expense of the esters and decreases the esters, due to the interaction taking place between an alcohol and acid mixture in presence of esters and water. When the low wines + feints + foreshot are subjected to hydrolysis under a reflux condenser a similar effect is observed on the total acids and esters. Further when hydrolysis for one hour is followed by distillation the cumulative effect is a smaller increase in the total acids and a smaller decrease in the total esters in the fractions.” One thing to note here is that I’m pretty sure Hastie is dealing with the second distillation where there is no non-volatile acids to catalyze esterification. So maybe esters are predominantly formed in the first distillation then unravel to a small degree during the second distillation then even reform post distillation as everything reaches an equilibrium. Non-volatile acids absorbed from the barrel, it should be remembered, will influence this equilibrium. The refluxing Hastie mentions has the effect of pushing the solution towards equilibrium but distillation is not at equilibrium because the alcohol water concentrations are always changing as vapor leaves the distill. The French also note that best results of double distillation are achieved if the second distillation happens quickly before the low wines can sit around and approach equilibrium.
“In these tests and in those which follow, the total amount of esters destroyed does not agree with the total amount of additional acid found, except in those cases to be given in detail below where alkali was added to the liquid before hydrolysis and distillation, the use of alkali limiting the number of possible reactions and allowing of more definite conclusions.” I don’t completely know how to interpret this. The only thing I can think of is that when ethyl acid is broken up it could become plain acetic acid or acetaldehyde. I can’t remember the names of the processes for aldehyde formation.
“This is probably a case of the reversible reaction known to occur between acids + alcohol and esters + water. The acid and alcohol heated together, yield esters up to the equilibrium point dependent upon the conditions of temperature and relative quantities of alcohol and acid present.” I think something he is missing is pH influence from other non-volatile acids. this comes into play during the first distillation where significant non-volatile acids are present and then again in the barrel where pH drops due to the accumulation of new non-volatile acids.
“[…] and although an equilibrium point should be reached theoretically after a definite amount of hydrolysis, this equilibrium point will never be actually attained in distillation as the total esters and alcohol vary in amount as distillation proceeds, and products pass to the distillate.”
Hastie goes on to explore distilling a low wines + feints + foreshots mixture in the presence of sodium hydroxide (lye) to see what happens. He determines that the formation of esters and the splitting apart happens simultaneously in the still.
“When the conditions are, as in practice, those of distillation, the hydrolysis of esters will occur, and the production of esters will also take place, but an equilibrium point will not in fact be reached, owing to the removal of varying amounts of the interacting substances to the distillate.” This lack of equilibrium is why new make spirits can change so markedly in the first few months.
One thing that definitely needs to be noted is that Hastie is only looking at the second distillation of double distillation. The first distillation is very different because of all the non-volatile material that influences pH and thus equilibrium and also possibly provides a fixative effect reducing the volatility of certain compounds.
from the discussion section worth noting:
“He did not agree with the suggestion that character might be determined by local bacterial conditions, so far as to account for differing whisky characteristics in the distilleries in a district.”