Scottish pot still variations

Scottish whisky distilleries accommodate a variety of different pot stills. Volumes vary from the 30963 litre wash still of Glenkinchie to the 2179 litre spirit still of Edradour (artisanal sma' stills excluded) and height from a couple of metres to the 8m tall Glenmorangie stills. Most are roughly onion shaped, but there are significant differences from the tear-shaped Bunnahabhain and Lagavulin to the slender Glenmorangie and Bruichladdich stills. Many stills have a wide bottom and a constricted neck, while several have a bulbous boil ball (aka reflux ball, Milton/Balvenie ball or bulge) in the middle section. Overall, the Scots are quite traditional with their stills, but occasional purifiers, still-neck coolers and a variety of condensers are still used. Most have converted to steam coil heating, while some still apply direct fire to the stills. In the history there has been a greater variety of stills, sadly more often to avoid taxation or speed up the distillation than to improve the distillate. In the 20th century the influence of North American distilling companies brought some interesting experiments with the reflux or Lomond stills, but the traditional pot still prevails in Scotland.

Tall Glenmorangie stills (photo: BBC)

Early distilling stills were usually quite small and direct-fired. There was not much of a commercial distilling until the 17th century. From 1644 the spirits in the United Kingdom were taxed by the gallon of proof spirit and the taxation did not really affect the distillation methods. Anyway, most distillers did not pay the taxes, as many distillers were just farmers saving the surplus grain for the winter as a spirit. In 1725 the malt tax was raised in Scotland to the English level. This caused riots and decreases in ale drinking, leading people to consume illegal spirits instead. In 1780 wine was taxed heavily and again the illegal distillers gained customers. A year later all private distilling was made illegal, though not to much effect in the Highlands. The use of mostly illicit stills affected the size of the stills used from the 18th century in the Highlands. They should be easy to transport or hide, so increasingly smaller stills were used as the Excise control became stricter in the late 18th century. 

Sma' still (decoration at Glenlivet, photo by mrtattiehead)

Due to rapid increase in illicit distilling, the crown allowed to licence over 20 gallon (91 litres) stills in the Highland area in 1784. As this did not have much effect, the limit was raised to 40 gallons (182 l) and all spirit exports from the Highlands were prohibited to England in 1785. At the same time the spirit duty was calculated according to the size of the still and the stills were assumed to be used seven times a week. This led to the use of very shallow 'Millar' pan stills from the 1790's, especially in the Lowlands, where the Excise surveillance was effective at least to some extent. The Lowland still was claimed to operate in 3 minutes, providing significant tax benefits, but extremely coarse spirits. The pan still was wide and shallow, usually just a few inches inches deep and usually just about over the minimum legal capacity. Additional upwards expanding coils or pipes were introduced into the still to maximize the evaporation at the bottom and condensation at the top.

Millar shallow stills (Forbes, 1948)

Lowland still sure was fast, but offered minimal reflux, copper contact and virtually no chance to cut the spirit correctly. So the coarse Lowland spirit often had to be rectified, ie redistilled or spiced heavily. Since the crown could not catch most of the illegal distillers and lost huge revenues because of the legal Millar stills, they decided to prohibit all stills under 2000 gallons (9092 l) in 1814. This effectively stopped pan distilling in the Lowlands, improving the quality, but put legal quality Highland distilling under ground until 1823, when taxation was eased considerably. In fact the over 40 gallons stills were legalized in 1816, but this had not much effect on the Highland stills or their desire to go legal.

Conversion to steam heating
*previously used steam jackets
**spirit still converted 2001

Another major improvement in efficiency was the use of steam, first directly on the pot or via a steam jacket, but later by indirect heating by steam coils. Direct steam heating for distillation was first implemented by dye manufacturers in the late 18th century with good heat economy. The first distillery to use direct steam heating of wash was English Mesly distillery in 1801. Indirect heating by steam jacket was used in Irish Roscea distillery in 1818, but the Excise Board rejected it because of difficulties in estimating the still capacity. The Coffey stills were heated by steam, but the pot stills were mostly direct-fired up to the mid 20th century. It was until 1887 Glenmorangie was the first Scottish distillery to use steam heating. Auchentoshan had steam jacketed heaters from early 1900s, but the majority of distilleries converted to indirect steam as late as the 1950-60s. In continental Europe and Scandinavia the steam heating became more widely used, especially after Savalle's invention of steam regulator in 1857.

Steam coils inside a spirit still

There are still Scottish distilleries using direct-fired stills; Glenfiddich, Glenfarclas and Macallan use direct-firing for both wash and spirit stills, while Springbank, Glen Garioch and Tobermory use direct-fired wash stills. Direct firing provides more temperature fluctuation both in the still and the contents. High temperatures can lead to burning and excess formation of furfural (nutty,burnt) or sulphurous and vegetal notes, especially if there is lots of sediment (dead yeast, grains) in the wash. To prevent this burning, direct heated wash stills have been installed with rummagers, ie rotating chains to keep the solids moving at the bottom of the stills.

Early 19th century was the golden era for still experiments. The still heads were adjusted in many ways; there were soap trays and stirrers to minimize frothing, steam coats to enable more even distillation and most importantly several means to enhance the reflux with boil balls, cooling condensers, refridgerators, trays and series of boiling chambers, which probably eventually led to the birth of the continuous stills by Adam, Fournier, Blumenthal, Stein and Coffey.

Balvenie spirit still with a boil ball

A common way to increase reflux was to shape the stills so that the rising vapours were cooled or exposed to lower pressure and copper. This was easily done by adding bulbs or balls in the still head. They were and are still common in the Speyside. Boil balls could be one reason for the perceived fruity and light "Speyside"-style of spirit, since they probably increase copper contact, reflux and ester formation, while decreasing the heavy oily and sulphury notes.

Still head cooler at Dalmore

Water cooling of the still head was probably first tested in late 18th century, the first patent is by Pontiflex from 1798, but the first Scottish distilleries to commercially cool their still heads were Hazelburn (1837), Dalmore (1839), (Ben) Nevis (1878), Fettercairn (1890) and Littlemill (1931). They used different methods for this, as Hazelburn had basically a tube condenser installed at the top of the still, where the spirit passed through pipes, which were cooled by water circulating in the condenser unit. Dalmore simply had a water jacket around the still head. Nevis, an extension of the Ben Nevis distillery, probably used a water jacket similar to the one in Dalmore, although there have been (unconfirmed) claims of a Lomond style cooled plate systems inside of the still. Littlemill had an early version of the Lomond still combined with water jacket coolers outside the still.

Nevis (Barnard, 1887)
Purifiers in the front left row, still head-cooler in the back

Intermediate condensing vessels between the still head and the worm were proposed already in 1736 by John Payne. The distilled wash or spirit is condensed inside a water jacketed purifier situated in the swan neck of the still and the heavier stuff is returned into the pot making the spirit lighter and higher in alcohol. Cooled intermediate condensers (water cooled purifiers) are still used at Glen Grant, Glen Spey and Strathmill distilleries.

Glen Grant uses purifiers on all stills

Glenugie purifier

Uncooled purifiers (basically a pipe descending from the lyne arm back to the still) are used in Ardbeg, Glenlossie and Talisker.

Ardbeg purifier (photo by www.coolhunting.com)

After the distillate leaves the still and there is no turning back via reflux or purifier, the spirit must be cooled. The traditional cooling method is a worm tub, consisting of a pipe wound into a spiral and immersed into a cold water tub. German chemist Christian Ehrenfried Weigel invented a worm tub in which the the cooling water was circulated to keep it cold (the Liebig condenser). The tube condenser with multiple straight copper pipes inside a cooled shell instead of a single coiled one in a tub was invented in 1825 by William Grimble. The shell and tube condenser provides more copper contact and is much more durable. A dozen Scottish distilleries still use worm tubs.

Disused worm at Auchentoshan

The Lomond still is a pot still with several horizontal (often perforated) plates inside the still neck. They became more popular in the Northern America and several bourbon and Canadian whisky distillers continue to use reflux stills, as they are often called over there.

Lomond stills at Glenburgie

The first commercial reflux still in Scotland was installed in Littlemill distillery in the early 1930s. American Duncan Thomas bought the distillery and apparently tried to produce light bodied Lowland whisky by two distillations with the reflux column and water jacketed cooler on the spirit still, instead of the traditional triple distillation previously used at the distillery. The double distillation with reflux column pot still was used at Littlemill until its closure in 1994. A similar experimentation was conducted in the 1950s by the Canadian company Hiram Walker & Sons. Their agenda was to produce a variety of different malt whiskies for blending purposes. To increase the control of the distillation reflux they used rotating rectifier plates, which could be turned to vertical or horizontal position for less or more reflux. The first such still was installed at Inverleven malt distillery situated inside the grain distillery Dumbarton in 1956. The resulting spirit was called Lomond whisky, hence the name Lomond still used later to describe all the Scottish reflux still whiskies. The experiment was successful, and the Canadians went on to install Lomond stills at Glenburgie (to produce Glencraig), Miltonduff (to produce Mosstowie) and Scapa. Scapa was different from the others, as it used a Lomond still in the wash distillation to render the spirit "sweeter and cleaner".

Lomond wash still at Scapa

Littlemill distillery owner Duncan Thomas founded the Loch Lomond distillery in 1966 with the American company Barton distillers to produce a yet wider variety of spirits (7) by altering the settings of the rectifier plates, but also the length and angle of the lyne arm by a peculiar turning telescope lyne arm. These adjustable lyne arms were also installed in Mosstowie and Glencraig later on.

The Scapa reflux wash still experiment was discontinued in 1971. The official reason for removing the rectifier plates was that the tube and shell condensers made the wash still plates futile. That sounds odd since the tube and shell condensers had been used for a century by then. The Lomond stills in Miltonduff and Glenburgie were mothballed in 1981, as the surplus of whisky resulted in rationalisation of the business and eventually forced Hiram Walker to sell out all their Scottish distilleries in the mid 1980s. Littlemill was mothballed in 1994 and destroyed in a fire in 2004. Duncan Thomas and Bartons sold Loch Lomond in 1971 to a private company, which keeps the reflux still distilling alive in Scotland.

A hybrid Holstein still from Germany
Copper pot still with a rectification column and a dephlegmator (cooling head) and a steel condenser

REFERENCES AND FURTHER READING:
Barnard A. The whisky distilleries of the United Kingdom. Birlin ltd 1887
Forbes, RJ. Short history of the art of distillation. Brill 1948

Hume JR, Moss MS. The Making of Scotch Whisky

Morewood S. A philosophical and statistical history of the inventions and customs of ancient and modern nations in the manufacture and use of inebriating liquors. Longman 1838.
Nettleton, W. The manufacture of spirits. London 1893
Reaich, D. Influence of copper on malt whisky character. In Proceedings of 5th Aviemore Conference on malting, brewing & distilling. 1998
Ronde I. Malt whisky yearbook 2015. MagDig 2014.
Russell I. Whisky. Elsevier 2003.

Townsend B. Scotch missed. Angel's share 2000.
Townsend B. The lost distilleries of Ireland, Neil Wilson 1997

Udo M. The Scottish whisky distilleries. Black&White Publishing 2006.

Weir, RB. The history of the Distillers Company 1877-1939, Oxford Univ Press 1995

Chill filtration

Same whisky, chilled with a drop of water on the left

Most of the Scotch whisky in the market is filtered in some way before bottling. The methods vary from crude physical filtering (ie spirit is run through a cloth or a cellulose sheet) to temperature and pressure controlled nanofiltering systems. 

The main reasons for filtering the spirits are removing any solid components, improving the flavour and avoiding the haze formation later in the bottle or glass. 

Spirits have been chill filtered at least from the late 14th century. Russian vodka was traditionally rapidly cooled after distillation with ice. The excess water transformed into ice and most of the oils hardened on top of that. Filtering became common before the 17th century. The early filters were usually made of cloth (felt, cotton), but also of paper, sand and charcoal. Chemical purification was also used quite early on, just as with wine, mead or beer. Spirit cleansing additives of the 17th and 18th century included ash, potash, burnt wormwood, and the gentry also used milk, eggs, fresh black bread, soda and isinglass to produce top quality vodka. 

Charcoal in Jack Daniel's distillery (alcademics.com)

Coal filtering was also widely used in USA and Canada in the early 19th century. In 1810's Kentucky "layers of white flannel, clean white sand and pulverised charcoal (about 20 inches thick layer) from good green wood such as sugar tree hickory" were used as a filter. The now famous Lincoln county process consisting of maple wood coal filtration at a thickness of 10 feet was invented in 1825 by Alfred Eaton and is still used by Jack Daniel's and George Dickel. Active charcoal was widely used from the start of the 20th century. The first written evidences of active charcoal filters are from 1785 from St Petersburg, Russia. Farmacist T.Y. Lowitz found that raw distillates became clearer and less harsh tasting after treatment with "raw coal".  The activated coal filtering was patented in 1901 in Austria and in 1907 in Russia and used widely ever since, especially in vodka production.

Sand and coal filter tanks in Zhitomir vodka distillery

The distillers filter their spirits for various reasons, most of which are based on traditional practices and empirical evidence, not much has been released as scientific papers. In Tennesee, the Lincoln County process is believed to reduce fusel oils and harsh flavours, resulting in a "less grainy" spirit, according to John Lunn, the master distiller of George Dickel. Most bourbons are filtered before and after aging with active charcoal, usually said to "mellow" the taste. In China, Japan and Taiwan the rice spirits are filtered to remove higher alcohols (fusels) to enhance the flavour. The vodka producers usually just try to remove any colour or taste to render the spirit "clean". Scotch whisky producers claim that their filtering does not affect the flavour and only prevents the haze formation in the bottle or glass. Actually, charcoal is not very efficient in removing oils from the spirit, at least at higher alcoholic strengths and the normal filtration of rice spirits removes only a small fraction of higher alcohols, although an extremely efficient nanofiltration can reduce higher alcohols up to 44%. Interestingly, the amounts of higher alcohols has quite dramatically dropped during the 20th century, which probably diminishes the clouding, but also must affect the flavour, both directly and through lesser high chain ester formation.

	EU limit [g/l]	Modern spirit, est.	Analysis 1905	Analysis 1966
Scotch malt	10	~ 1	1,5-3,5	2,7-3,9
Scotch blend	10	<1	0,5-1,9	1,7-2,2
Scotch grain	10	<1	0,5-3,0	0,7-1,3
Bourbon	10	~ 1,5		5,9-6,8
Rice spirits	10	2-5
Rum	2,25
Fruit brandies	2
Marc	1,4			3,5-4,5
Brandy	1,25	<1		1,5-5,7
Canadian whisky	10			1,15
Irish whisky	10			6,95

Amount of higher alcohols in different spirits [g/l]

The haze formation occurs when the long chain fatty esters become insoluble in lower temperatures or at lower alcoholic strengths. The most crucial esters in haze formation in whiskies are ethyl laureate (ethyl-dodecanoate), ethyl-palmitate (ethyl-hexadecanoate) and ethyl-9-hexadeanoate (ethyl-palmitoleate). Alcocol content of 45% abv is believed to be a crucial limit for these long chain esters to percipitate in room temperature. Other compounds responsible for the cloudiness are high molecular weight lipids, especially sitosterol beta-D-glucoside (probably cask-derived) and slightly ethanol-soluble lignins from the cask.

The haze-forming long chain esters are not very aromatic, ethyl laureate gives some floral, fruity and waxy aromas, as ethyl palmitate and ethyl palmitoleate mostly contribute to the mouthfeel (waxy, oily), although they are reported to give some aromas of coconut and fruits. Probably the more important factor is their ability to act as a surfactant and to enhance/suppress other aromas.

(Coal) filtering increases the formation of short esters and the conversion of aldehydes and ketones to alcohols, probably because of the slight oxiditation caused by the process. On the other hand, some (7%) ethyl acetate (pear-drops) was removed in a typical Scotch filtration, so the net effect remains unclear. The highly efficient nanofiltration and active coal filtration techniques used by brandy and vodka industries remove great deal of long esters and some terpenes. Even a light filtration removed all of the nerol (rose,lemongrass) from apricot brandy and the same probably happens in Scotch whisky filtration. Studies on Glenlivet malt whisky indicate that significant amount of gallic acid was removed in filtering, but the same study found no difference on nosing aroma.

Plate and frame filter in a bottling plant

A typical filtering method used in Scotch whisky industry is a plate and frame filtration with cellulose sheets, medium pressure and cool temperature. Depending on the source the temperature of whisky is lowered usually to +5 - +10C, although some apparently use even colder temperatures (down to -10C?). According to Glenmorangie the cold stabilisation time is 3 hours and apparently up to 24h in some other bottling plants. In the 1990s all of the filters used in Scotch whisky industry were of the plate and frame type. Some distillers have at least experimented with easier and cheaper membrane filters, but there is little information about whether they are in use at a larger scale. The pressure use in the plate and frame filters is usually between 20-60 psi (138-414 KPa), a higher pressure means faster but less complete filtration. The particle retention size is 5-7µm, at least in one bottling plant. Compared to the modern nanofilters at 10nm (0,001µm), that is quite crude.

Plate and frame filter (whisky.com)

Because the filtration processes are not uniform in the Scotch industry, it is not clear how much the process affects the flavour. Certainly you can change the flavour profile and the mouthfeel of an estery and oaky whisky with slow cold filtration. A too strict filtration would likely dimish waxy/oily mouthfeel and floral, fruity and oaky aromas. Whether the current filtering practices do that, is uncertain.

References and further reading.
Braus H et al. Isolation and identification of a sterol glucoside from whiskey. Agr Food Chem 1957;5(6);458-9
Da Porto C. Effects of chill filtration on the composition of grape spirit. Wein-Wissenschaft 2000;55(1);7-12
Duarte FC et al. Physicochemical and sensory changes in aged sugarcane spirit submitted to filtering with activated carbon filter. Ciênc Tecnol Aliment.,2012;32(3);471-477
Glaub, R et al. Effects of various filter systems on sensory quality of fruit brandies. Kleinbrennerei 1998;50 (1);6–12
Himmelstein L. The king of vodka. Harper 2010
Hsieh CW et al. Develop a novel method for removing fusel alcohols from rice spirits using nanofiltration. Food Sci 2010;75(2); 25-29
Ko W et al. Removal of higher fatty acid esters from Taiwanese rice-spirits by nanofiltration.  p353. In Distilled spirits, ed Walker GM et al NOttingham Univ Press 2012.
Lachenmeier D et al. Defining maximum levels of higher alcohols in alcoholic beverages and surrogate alcohol products. Reg Tox Pharm 2008;50;313-321
Miljic UD et al. The application of sheet filters in treatment of fruit brandy after cold stabilisation. Acta per tech 2002;44;87-93
Taylor AJ, Mottam DS. Flavour science: Recent developments, RCS 1996
Persson KM. Med kol och kolonn. Spiritus 2005;7
Piggott JR et ak. The science and technology of whiskies. Longman 1989
Pirie G et al. Membrane filtration of whisky. Food & Drink 2000; p9-13. IChemE 2000.
Pokhlebkin W. A history of vodka. Verso, 1992
Puskas V et al. Influence of cold stabilisation and chill membrane filtration on volatile compounds of apricot brandy. Food Bioprod Proc 2013;91;348-351
Schidrowitz P, Kaye F. The determination of higher alcohols in spirits. Analyst 1906;31;181-194
Singer DD. The analysis and composition of potable spirits. Analyst 1966;91;127-134
Wisniewski I. Filtering out. Whisky Magazine 2011;97;27
Malt Maniacs E-pistle: http://www.maltmaniacs.net/E-pistles/Malt-Maniacs-2011-06-Chill-filtration-and-cloud-formation-in-whisky.pdf
Whisky.com study: http://www.whisky.com/information/knowledge/science/study-on-the-chill-filtration-of-scotch-single-malt-whiskies.html

Copper

Glenfiddich still room

Scotch malt whisky is distilled in copper pot stills. Copper is used for its malleability and heat conductivity, but mainly because it is believed to render the spirit less sulphury and more refined. Surprisingly little is known about the mechanisms and chemistry behind the positive effects of copper to the spirit.

Copper is the traditional material for Scottish stills, but the first distillers of aqua vitae were most likely using pots of clay or glass. In Asia, clay and porcelain pots with bamboo condensers were used. Quite minute quantities of spirits were prepared before the 14th century. As metallurgy improved and distilling became a larger scale operation, the stills were forged from tin, iron, brass and copper. Copper was easiest to keep clean, not too heavy and relatively easy to forge, so it became the common still material, at least in Britain and France quite early on, probably in the 15th century.

Indian still from 18th century

According to Samuel Morewood in 1838, most European distillers were using copper stills, although poorer distillers still used some tin, pewter and even wooden stills. Copper was preferred and Scottish illicit distillers considered that at least the bottom and the worm of the still should be copper, but tin was often used in the body of stills. At the time Indian distillers preferred clay pots with copper head, which was cooled by cowdung which was kept moist by cool water. In Java copper stills and Banca tin worms were used. In the British Caribbean (Jamaica, Trinidad, Barbados) mostly copper stills were used, but in the French and Dutch Caribbean (Guadaloupe, Marie Galante, Martinique, Guyana, St Martin) there were many different still types, probably of French inspiration, constructed of copper, iron and wood.

Copper is often claimed to suppress the amount of sulphury compounds in the spirit, but there is really quite a little research or even theoretical understanding about the phenomenon. The most predominant effect promoting the sulphury aroma in spirits is dimethyl trisuphide (DMTS). Its perception treshold is about 0,1µg/litre and the typical concentrations in spirits vary between 1-6µg/litre. The amount of DMTS has been shown to diminish in the spirit by the copper influence. However, not just any copper influence has that effect. For example, by using copper salts in a glass still increases DMTS, but copper wool in a glass still decreases DMTS, just not as much as a copper still. In addition, an used and patinated copper still seems to be more effective in DMTS-reduction compared to clean copper. To make things even more complex, the other metal ions and the antioxidant potential of the wash change the settings of the system once more. For example, iron decreases the copper effect, but ascorbate (by acid or antioxidant effect?) increases the DMTS formation. Most common aromatic sulphury compounds present in the wash are (pot) distilled just about in the same quantities over to the spirit, whether a copper or steel still is used, including DMS, DMDS, MMFDS, thiophene, thianaphthene and S-methyl thioacetate.

Levels of sulphur compounds in new make from copper and stainless steel stills (Harrison 2011)

Another important effect of copper is its catalyst role in converting thiols and mercaptans to usually less pungent compounds in presence of carbonyls. Methanethiol (CH3SH) is abundant in nature and in small quantities it contributes to the aromas of nuts and cheeses, but in higher concentrations it smells like rotten vegetables. Mercaptans and thiols are formed in some extent by the yeasts as byproducts, but especially in the event of anaerobic (non-lactic) bacteria infection of the wort.

There is some evidence of increased ester formation from acids and alcohols during the distillation, but that may happen in higher temperatures anyway and have nothing to do with the copper. Copper seems to have some effect on phenols, decreasing slightly the amount in the distilled spirit.

Copper plates in a column still

Ethyl carbamate (EC, urethane) was a hot topic in the 1980s, as it was found to be carcinogenic and to increase during maturation phase of spirits. At the time various whiskies, especially grain or bourbon whiskies from stainless steel column stills were producing spirits with way too much EC and the concentrations seemed only to increase during maturation. It was found that copper in the ascending phase on still decreased EC dramatically and copper was (re)introduced into column stills. Adversely copper salts in the new make does catalyse the EC formation during the maturation, so most grain distillers use only stainless steel in the condensers to dimish the amount of copper residues in the new make.

The most influential part of distillation in terms of sulphur (DMTS) removal is in the spirit still body and interestingly in the vapour phase of the wash still, but not as much in the wash still body or the spirit still vapour phase. Alcohol concentration might play a role in the catalyst properties of copper. The spirit still condensers at the end of the second distillation have the least effect to the DMTS removal, on the other hand (at least in the column stills) the late phase condensers are shown to be important in conversion of dimethyl sulphide (DMS) to less aromatic sulphide.

DMTS in the new make.(C=copper still, S=stainless steel still, S1=copper in wash still body, S2=copper in wash still lyne arm, S3=copper in wash condenser, S4=copper in spirit still body, S5=copper in spirit still lyne arm, S6=copper in spirit condenser) (Harrison 2011)

Reflux is important factor in copper influence. It means the amount of vapour condensed and trickled back down to the still from the head and lyne arm instead over to the condenser. Reflux depends on the charge (fill level) of the still, whether the wash is cooled or preheated, the shape of the still, the speed of distillation and the cooling of the still and the condensers. High reflux is achieved by low preheated charge, big tall narrow stills with boiling ball and steam coils, ascending lyne arm and efficiently cooled tube condensers. High reflux means lower DMTS and phenols, but higher esters and high alcohols, producing fruity clean spirit. Low reflux gives full, meaty, phenolic, robust new make. Esters apparently follow an U-curve, so that very low or high reflux produces more esters than an average one.

Lomond  wash still in Scapa

In the 1950s a Canadian company Hiram Walker tried to gain access to Scottish malt whisky markets. They owned six malt distilleries and the Ballantines brand. Only six different malts were considered inadequate for blend production and at the time competition was harsh, so they decided to experiment with pot stills installed with rectifier plates inside the head of the still. By turning and adjusting the number of the plates they were able to adjust the reflux and copper contact. First such still was installed at Inverleven (inside the grain distillery Dumbarton) in 1956 and the resulting spirit was called Lomond whisky, hence the name Lomond still. The experiment was successful, and Hiram Walker went on to install Lomond stills at Glenburgie (to produce Glencraig), Miltonduff (Mosstowie) and Scapa. Scapa was different from the other, as it used Lomond still in the wash distillation to render the spirit "sweeter and cleaner". Loch Lomond distillery was founded in 1966 and it produced a variety of spirits (7) by altering the settings of the rectifier plates, but also the length and angle of the lyne arm by a peculiar turning telescope lyne arm, which was also installed in Mosstowie and Glencraig later on. Scapa experiment was discontinued in 1971, as better condensers made the wash still plates futile. The Lomond stills in Mosstowie and Glencraig were mothballed in 1983, as the surplus of whisky resulted in rationalisation of the business. The rectifier plates did change the spirit qualities, bu according to still men, they were very hard to keep clean and they accumulated lots of residue when turned fully horizontally. The cleaning problem became even worse by the introduction of solid yeast in the 1970s. Probably tube condensers were easier and even more effective in sulphur removal, although maybe ester formation was theoretically better in the rectifier plates. Loch Lomond distillery still produces Lomond-style whisky.

Just to put the theory to the test, below are the lyne arm angles and spirit still sizes of 24 Scottish malt distilleries compared against lightness-richness value given for the basic ~12yo malt of the distillery by Dave Broom in The World Atlas of Whisky. There is some, but not significant correlation between the lyne arm angle and the richness of whisky, but no correlation between the spirit still size and the perceived richness. Of course there are many other aspects affecting the products of the distilleries. Would have been too simple, if there was a clear correlation between either one...

Some correlation between lyne arm angle and richness of the basic OB

No correlation between spirit still size and richness of the basic OB

References and further reading:
Alcarde A et al. Ethyl carbamate kinetics in double distillation of sugar cane spirit. J Inst Brew 2012;118;352-5
Broom D. World atlas of whisky. MItchell Beazley 2010
Bryce JH et al (ed). Distilled spirits: Production, technology and innovation. Nottingham Univ Press 2008
Forbes, RJ. Short history of the art of distillation. Brill 1948
Harrison, B et al. The Impact of Copper in Different Parts of Malt Whisky Pot Stills on New Make Spirit Composition and Aroma. J Inst Brew 2011;117(1);106-112
Hernández-Gómez L et al. Melon fruit distillates. Food Chem 2003;82;539-543
Jack, FR et al. Sensory implications of modifying distillation practice in Scotch malt whisky production. In Distilled Spirits, ed Bryce JH, Piggott JR, Stewart GG. Nottingham Univ Press 2008.
Lima U et al. Influence of fast and slow distillation on ethyl carbamate content and on coefficient of non-alcohol components in Brazilian sugarcane spirits. J Inst Brew 2012;118;305-8
Masuda, M and Nishimura, K. Changes in volatile sulfur compounds of whisky during aging. J Food Sci 1982; 47(1); 101-5
Monica Lee KY et al. Origins of flavour in whiskies and a revised flavour wheel. J Inst Brew 2001;107(5);287-313
Morewood S. A philosophical and statistical history of the inventions and customs of ancient and modern nations in the manufacture and use of inebriating liquors. Longman 1838.
Nedjma M, Hoffmann N. Hydrogen sulfide reactivity with thiols in the presence of copper in hydroalcoholic solutions or cognac brandies. J Agric Food Chem 1996;44;3935-38
Nóbrega I et al. Ethyl carbamate in cachaça. Food Chem 2011;127;1243-7
Prado-Ramírez R et al. The  role of distillation on the quality of tequila. Int J Food Sci Tech 2005;40;701-8
Reaich, D. Influence of copper on malt whisky character. In Proceedings of 5th Aviemore Conference on malting, brewing & distilling. 1998
Riachi L et al. Review of ethyl carbamate and polycyclic aromatic hydrocarbon contamination risk in cachaça and other Brazilian sugarcane spirits. Food Chem 2014;149;159-169
Russell I. Whisky. Elsevier 2003.
Walker GM, Hughes PS (ed). Distilled spirits, new horizons: energy, environment and enlightenment. Nottingham Univ Press, 2010 

Bengt Thorbjörnson in Scotland, 1929

Bengt Thorbjörnson (1891-1975) was a Swedish chemical engineer. After graduating from Kungliga Tekniska Högskolan of Stockholm he worked in sulphite factory in Bergvik (1916-1917), which manufactured sulphite spirits as a side product from 1911 at least until 1917. In 1917 he moved to Kramfors to work in a cellulose factory (1917-24) also producing industrial spirits as a side product. After a short spell at a margarin factory in Kalmar (1924-26) and a visit to Nashwalk Pulp & Paper Co in USA (1924-1925) he was appointed as the chief chemical engineer for Vin & Sprit AB (Wine & Spirit). He continued to work for the biggest Swedish alcohol producer for 30 years until 1957.

Bengt Thorbjörnson on the left

 Thorbjörnson toured Scottish whisky retailers and distillers in 1929-1930. The main object was to investigate whether it was profitable to start whisky production in Sweden. After the tour the Finnish alcohol monopoly consulted Thorbjörnson on the same subject and the record of the Scottish tour is still available in Swedish from the Kansallisarkisto (The National Archive) of Helsinki. Thorbjörnson visited the warehouses of W.H. Chaplin, John Walker & Son and The Distillers Company, as  well as the distilleries in Caledonian, Mortlach, Cardow (Cardhu), Glen-Mhor, Glen Albyn and Adelphi.

He preferred the Highland malts and considered the Campbeltown malts were "lacking midtaste". The factors most affecting the flavour of whisky according to his studies were: 1) Water, which should be low in calcium. The water of River Spey was good as it ran through soil rich in granite and sand. 2) Climate, which should be quite cold but even to allow long stable distilling times. 3) Amount of peat used in drying the malt. 4) Bacteriae flora, as the local bacteriae influenced the quality of the brew. 5) Experience of staff. 

The first place to visit was the wine and spirit retailer W.H.Chaplin & Co in London, who were at the time the sole representatives of the popular Long John brand. Their warehouse at Tower Hill consisted of 10 floors, of which 3 were underground. Huge glazed concrete cisterns (136 000 l) were used to vat and cold-chill-filter port wine. The whisky was vatted on demand in smaller concrete vats of size about 22 000 litres from different casks and different distilleries. According to other sources, Ben Nevis was the leading malt for Long John.

At John Walker & Son Thorbjörnson was hosted by the manager Sir Alexander Walker. At the time their Johnnie Walker blend was the most sold whisky brand in the world. Only sherry casks were used at the time. About 20% of them were new casks seasoned with sherry and the rest were refill casks rejuvenated with a small amount (about 35 litres) of sweet dark sherry for six weeks during which they were turned regularly. After the sherry-seasoning they are treated with pressure to impregnate more sherry into the wood. The sherry in the cask was then poured off and used several times for other casks. The pressure treatment had been developed by WP Lowrie in late 19th century and at the time of Thorbjörnson's visit it was used by many other blenders and distilleries as well. The Walkers had recently shifted to mainly hogshead size casks to ensure even quality. At the present time the Johnnie Walker recipe consisted of 10 parts Highland malt (Mortlach, Benrinnes, Ord, Cardow, Glenlossie, Dailuaine, Aultmore, Coleburn or Clynelish), 2 parts of Islay malt (Talisker (classified as Islay!), Caol Ila or Lagavulin) and 2 parts of Lowland malt (Rosebank or Glenkinchie). The blended malt was then again blended with grain whisky (mostly Caledonian) and the malt content varied between 40-60%. Long John blend consisted of 65% grain, 15% Lowland malt, 15% Highland malt and 5% Islay malts.

Caledonian distillery in 1966 (scotlandsplaces.gov.uk)

Caledonian grain distillery produced 40 000 gallons per week, which equalled 9 000 000 litres 50% abv- spirit per year. Maize was the most common cereal, but wheat and barley were sometimes used, too. About 30% of the mash came from barley malt dried over coal fire to gain diastase power. The maize flour was pressure cooked to prevent bacterial contamination. Brewers' yeast from Edinburgh was used to ferment in covered washbacks of 225 000 litres capacity (Cardow used pressed yeast). Carbon dioxide was collected and sold to mineral water producers. Column distillation with 20 plates in the analyser and 40 plates in the rectifier was used to produce new make spirit of 67 degrees over proof (95,3% ABV). The spirit was cut with water to 11 over proof (63,4% abv) for maturation. Draff was given for free to farmers. At the Adelphi grain distillery weekly production was 36 000 gallons/week and the only significant differences were the cooking of maize (not pressurised in Adelphi) and the fermentation time (72h in Adelphi, 96h in Caledonian). About 125 men were employed in each.

Mortlach produced high quality Highland malt with "quite old-fashioned means". A total of 24 men were employed to produce 8 000 gallons per week. Production was bigger than at the Invergordon distilleries, as Glen-Mhor and Glen Albyn managed only 2 500-3 000 gallons per week each. Distillation was carried out from September to end of May and the spring production was considered to be of the best quality. Mostly foreign barley was used and floor malted on site. Two kilns were used to dry malt for 50 hours in up to 77C after 9 days of germination. About 18 kg peat for every 120 kg of coal was used in kilning. Fermentation time in seven 60 000 gallon washbacks varied between 46-56 hours. After each fermentation the washbacks were washed with lime and peat was burned on the bottom of the washback to avoid bacterial contamination. The spirit was double distilled (no mention of the Wee Witchie or even partial triple distillation) to a very high proof of 45 over proof (82,8% abv) and reduced to standard 63,4% before maturation. Rummagers for wash still and direct firing with coal for both stills were used. 

Thorbjörnson calculated that the blending and maturation was cheaper in big English warehouses compared to the Swedish Reymersholm or Slottet warehouses. He also thought that the flavours came mostly from the malt whiskies and therefore the malt content of the Swedish blends (Crown Blend and Black Label) should be increased. On the other hand Scotch grain whisky could be replaced with cheaper domestic neutral potato spirit to cut costs. He also made a a costs-analysis for building a Swedish malt distillery with a 500 000 litres capacity per 6 months, which apparently never came to be.

References and further reading:
Kansallisarkisto, Helsinki. http://www.arkisto.fi/en/the-national-archives-service/arkistolaitoksen-vaiheet-2

Koch B. Från idé till produkt. Svenska Uppfinnarföreningen, 1963.

Morrice, P. Schweppes guide to Scotch. Alphabooks 1983
Spiller, B. Cardhu. John Walker & Sons, 1985.

History of the column still

Coffey still

Whisky can be distilled in column or pot stills. Grain whiskies are usually distilled in the faster and more economical column stills, which produce light or almost neutral spirit opposed to the heavier malt whiskies produced usually in pot stills. 

Distilling wine was invented in northern Italy during the 11th century, although the Arabs and the Alexandrians had probably used distillation before that to produce infusions and concotions, perhaps even as early as in the 1st century AD. The early stills were simple pot stills with a collection pot. The apparatus was often made of clay and/or copper, sometimes partly of wood, even of leather. The shape of still was usually onion-like; wide bottom to enable efficient and fast heating and narrower head to enable condensation and collection. Some kind of worm was used from the beginning, but efficient water cooling was probably invented as late as in the 18th century. The knowledge of distillation spread through Europe and Russia during the 14th and 15th centuries and malt spirits were probably distilled in Britain and Ireland at least from the late 15th century. The design of the stills remained quite constant from the 11th to the 19th century, although there were numerous experiments with different shapes. The onion pot still however remained the still of choice until the early 19th century. Heating was provided by a naked flame, often by wood fire in southern Europe, but more often by peat in the north and after the 17th century by coal.

Water-jacketed still was invented in 1526 by Paracelsus (alias Theophrastus Philippus Aureolus Bombastus von Hohenheim the Swiss) and it became known as the Baine Marie or balneum Mariae among the alchemists. The water bath allowed the still to be indirectly heated, thus preventing the wash from burning on the bottom of the still and allowing the distillation of pomace and other thicker washes. The risk of cracking stills, especially made of clay, was also diminished by indirect heating. The fractionating system was invented as early as 1553 by German chemist Philip Ulstadius, but it did not possess any significant advantages for spirit distillers and was used primarily by (al)chemists.

The condenser was improved by a German chemist Christian Ehrenfried Weigel in 1771. He placed the worm into a tube, which was cooled by circulating cold water. The invention was named Liebig condenser. Later an englishman William Grimble invented the tube condenser 1825 and it was later improved and distirbuted widely by the Dutch still-manufacturer Armand Savalle.


The Woulfe bottle

The evolution of the still gained pace during the early years of 19th century, especially in France. An illiterate French workman Edouard Adam from Rouen attended chemistry lectures given by professor Laurent Solimani. Adam understood that the principles of the Woulfe bottle, invented by Angelo Saluzzo and used in chemistry, might also work for alcohol distilling and in 1801 invented and patented the first still to produce alcohol in one operation. In principle, that was the first working column still, although the "column" was placed horizontally and consisted of several chambers or pots. It allowed single distillation for high alcohol spirit, more effective heat exchange and relatively simple fractioning of the spirit. Mr Adam was however not successful in commercializing his invention and several distillers, including Solimani, Bérard, Barré, Brugniére, Pistorius and Carbonel, built either direct copies or similar stills with just minor modifications. The three distilleries built by Adam were not successful and he died poor in 1807.


Nääsi distillery, late 19th century Finland.
Pistorius still on the right, Savalle still at the back

Pistorius improved the Woulfe bottle principle and patented his still in 1817. It had many properties of a modern column still; the wort was fed into the rectifying part of the system and divided by the steam rising from the lower pots into alcohols, feints and the rest was piped to be redistilled in the lower pots. The rectifying plates are unique, but quite efficient allowing good reflux but also thick worts. The Pistorius still was used in central Europe and Scandinavia throughout the 19th century.

Armagnac still

The first truly continuous still was made by Fournier, who used two columns, which were heated alternately and fitted with valves for removing the residues. Professor Solimani introduced indirect steam heating for an modified Adam still in 1814 in his own distillery. French Jean Baptiste Cellier Blumenthal invented the first practical continuous still in 1808 and patented it in 1813. Basically he combined Adam's principle of multiple distilling/rectifying chambers, the early ideas of fractionation by Ulstadius, preheating and the vertical columns and the residue removal of Fournier. The apparatus still had a pot still, but the wine was feeded straight from the top of the column while vapours rose from the pot to the vertical distilling column, which had 9 perforated rectifying plates. Thus the distilling column was cooled with wine, which was simultaneously preheated for the distillation. The first stills were built by Cellier and a Dutch sugar-trader Armand Savalle, later to become a global still-manufacturer. The patent was improved with fractionating plates and draff/residue outlets and sold to Parisian apothecary Louis-Charles Derosne in 1818, who succeeded in commercializing the product. Savalle and his family continued with the original apparatus and sold them to various distilleries around the world. Some of their stills are still in use at rum, brandy and neutral spirit distilleries. Many eau-de-vie, armagnac and bourbon distillers adopted a cross-over between column and pot stills. The wort is boiled in the pot and rectified in single column with a lot of reflux.



Savalle still in Demerara Distillery, Guyana
(www.cocktailsoldfashioned.de)

In England a version of the Cellier Blumenthal still was patented in 1815 by relatively unknown Mr. Dihl, but it did not gain commercial success at the time. In the same year James Miller patented a system for preheating the wash in the worm cooler and in 1818 Joseph Corty described a still with double pots and a Pistorius-like condesenser-reflux-system. So basically all the pieces for working continuous still were available in Britain in the late 1810s. In Ireland the big pot stills ruled, although there were some experiments made with continuous distilling. John Stein at Clonmel distillery developed a triple still, basically just three stills attached to each other and Joseph Shee of Cork had a quadruple pot still, in which the first pot acted as a steam source. In 1822 Irish Andrew Perrier patented his vertical continuous still, which strongly resembled the Fournier and Cellier Blumenthal stills and by 1823 a French immigrant, a veterinary surgeon Jean-Jacques Saintmarc build a variation of the Adam still. The Saintmarc's potato spirit was not a success in England and he advanced into Ireland in 1825 and marketed grain whisky distilled with a continuous column still, but that was considered "too pure". It was until 1828 that the first commercially successful column still was built on the British Isles as Robert Stein, a member of the Stein-Haig distilling family, patented his column still. It had three preheaters and steam boiled in a separate vessel was used to heat the wash, which was intermittently sprayed by pistons into a series of chambers. The chambers were divided by crude cloths (probably haircloths). The cloth permeated ethanol well, but less so water and solubles, therefore acting both as a rectifier and a filter. It enabled large amounts of distillate to be produced in a single run and improved the heat economy compared to the pot stills. The process had to be stopped for discarding the excess oily residue, so it was not exactly continuous operation. Surprisingly the Steins used only malted barley in their Kirkliston distillery for several decades, despite the fact that most of the output was sold for gin manufacturers.

Aeneas Coffey (1780-1852)

The French-born Irishman Aeneas Coffey had retired from excise officers duty in 1824 and bought into Dodder Bank distillery in Dublin. He also managed the South King Street distillery (1828) and the Dock distillery (1834) in Dublin. The first Coffey stills were made of wood and iron and consisted of a single column, but copper plates and metallic columns quickly became the norm, most likely because of the better malleability and spirit quality. By the time Coffey patented his still design in 1830, he had introduced perforated copper plates for rectifying and pipes to remove the residual oils during distillation. During the 1830s the system was divided into two columns as it was easier to manufacture, it had better rectifying qualities as well as better heat economy. Numerous designs for rectifying plates were later introduced, although the most common was the bubble cap design. The Irish distillers trusted their big pot stills and only some Northern Irish distillers experimented with the Coffey stills, first in Derry by Andrew Alexander Watt's Abbey Street Distillery in 1833 and later in Belfast at Avoniel distillery (1882) , The Irish distillery, The Royal Irish distillery (the 1890s) and and at Dundalk (the 1880s?) distillery just south of the present border. As his stills were not selling in Ireland, Coffey moved his business to London. The first Scottish whisky distillery to install Coffey still was Grange in 1834 and during the next few years Inverkeithing, Bonnington and Cambus followed. Aeneas Coffey Jr tried his hand at Lewisham distillery, London in 1840, but was not successful and the Coffeys established themselves as still makers. At first the columns stills were used by rectifiers and gin distillers, but during the mid-1840s the Scottish distillers really started building Coffey stills.

Distillery	Still	Year
Kirkliston	Stein	1828
Cameron Bridge	Stein	1830
Grange	Coffey	1834
Inverkeithing	Coffey	1835
Bonnington	Coffey	1835
Cambus	Coffey	1836
Yoker	Stein	1845
Kilbagie	Coffey	1845
Port Dundas	Coffey	1845
Seggie	Coffey	1845
Glenochil	Stein	1846
Haddington	Coffey	1846
Croftanrigh	Coffey	1846
Kennyhill	Coffey	1847
Sunbury	Coffey	1849
Carsebridge	Coffey	1852
Saucel	Coffey	1855
Glenmavis	Coffey	1855
Caledonian	Coffey	1855
Bo'ness	Coffey	1876
North British	Coffey	1885

The Scottish patent still whisky distilleries founded in 19th century

The column still was much more efficient compared to the traditional pot still, producing higher proof (usually 86-95% ABV) spirit about ten times more in volume compared to medium sized pot still distillery. Since the malting, heating and maintenance costs were a fraction of those of a malt distillery, the column still grain spirit cost about 50-70% less compared to pot still malt whisky, even if the set-up costs were included. The northern Britons were not used to the light column still whisky and at the beginning large quantities were sold to rectifiers and gin distillers, who spiced the spirit and sold it as gin or imitation brandy or cognac. As shown in the figure below, the English rectifiers and distillers quickly adopted the Coffey still, but the more traditionalist Irish and Scots remained loyal to the pot still at least to some extent.

(Weir 1995)

During the latter part of the 19th century several factors caused the rise of the column still whisky. Branding and advertising became important at about the middle of the 19th century Britain. Several traders begun blending the products of different distilleries and sold them under their own labels. Blending enabled the inclusion of raw grain column still spirits into the mix and on the other hand blended whisky was easier to sell in the big English markets used to lighter non-smoky spirits. The column distillers began to control their pricing, the first price cartel was formed in 1856 and by the 1890's the century the DCL controlled all but most column distilleries and had a virtual monopoly during the 20th century. The tax reform in 1860 raised the taxation of foreign spirits and fortified wines and allowed commercial yeast manufacturing in the distilleries, which became a substantial source of revenue for the grain distillers towards the turn of the century.

REFERENCES AND FURTHER READING:
Barnard A. The whisky distilleries of the United Kingdom. Birlin ltd 1887
Forbes, RJ. Short history of the art of distillation. Brill 1948
House, J. Pride of Perth, Bell's 1976
Kaukoranta, A. Sulfiittispriiteollisuus Suomessa. Polar 1981
Kauppila, O. Rajamäen tehtaat. Painokaari 1988
Laver, J. The house of Haig, Haig 1958
Morewood S. A philosophical and statistical history of the inventions and customs of ancient and modern nations in the manufacture and use of inebriating liquors. Longman 1838.
Nettleton, W. The manufacture of spirits. London 1893

Townsend B. Scotch missed. Angel's share 2000.
Townsend B. The lost distilleries of Ireland, Neil Wilson 1997

Udo M. The Scottish whisky distilleries. Black&White Publishing 2006.

Weir, RB. The history of the Distillers Company 1877-1939, Oxford Univ Press 1995
http://www.cocktailsoldfashioned.de/2011/02/demerara-distillers-limited-guyana-rum/

A modern Coffey still in North British distillery