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 

Fermentation waters

Glenlivet is one of the few Scottish distilleries using hard water,
but nobody told the AD.

Water is used in several phases of whisky production: steeping, mashing, cooling and dilution. Formerly water mills provided much of the energy needed in many distilleries as well. Distilleries have often been founded into places where water is easily available and it is believed at least in the marketing departments that fresh spring water or picturesque peaty burns play a significant role in the manufacturing process.

The most important attributes of steeping and mashing water are its hardness, pH, overall mineral content and microbiological purity.

Water hardness means the concentration of multivalent cations in the water, ie the amount of ions with a charge of +2 or more (mainly calcium and magnesium) and it is usually expressed as concentration of calcium carbonate (CaCO3) in the water. Soft water is defined as containing under 40-100 mg/l and hard water over 80-200 mg/l of CaCO3, depending on the source.

The pH (pondus hydrogenii) of water means the activity of hydrogen atoms in the water. The pH value describes the acidity of the water in logarithmic scale, ie pH 4 is ten times more acidic than pH 5 and hundred times more acidic than pH 6.

The malt or grain is another source of acidity in the mash. The darker the roast of the malt, the more acidic it gets. Therefore soft alkaline water is often preferred for brewing pale malts and hard water for darker acidic malts. The malts used in whisky production are as pale as possible to ensure the best alcohol yield. The commonly desired pH for mash is about 5-5,5, a lower pH might cause excessive lactic acid bacteria production and a higher pH a slower or incomplete fermentation. Calcium is the most important mineral affecting both the pH and water hardness. Calcium itself does not taste of anything at usual concentrations, but it lowers the pH, increases water hardness and yeast flocculation and might reduce magnesium making the flavour less sour.

Other important ions in the brewing waters are sodium (Na+) and the common anions; sulphate (SO4^-2), chloride (Cl-) and carbonate (CO3^-2). Sodium softens the water by decreasing the effect of CaCO3 and at higher concentrations (over 50 ppm) makes the water sweet, or even salty (>150 ppm) and sour (>250 ppm). Sulphate enhances bitter, dry and sulphury flavours, complimenting the hoppy aromas of beers and providing antibacterial influence in  both fermentation and bottle-aging, reducing the lactic acid bacteria growth. Chloride enhances malty flavour, but at high concentrations it might give pasty, salty or chlorine aromas. None of Scottish distilleries use chlorinated water for their fermentations.

The local water quality was probably one of the reasons why brewers in Burton-on-Trent and Edinburgh went for bitter highly hopped IPAs (high CaSO4), in Pilzen for light crisp lagers (extremely soft water), in Münich for darker lagers (higher CaCO3), in Dublin for dark stout (high CO3^-2, low Na+ and relatively low Ca+2) and in London for dark sweet porter (high CaCO3 and NaCO3).

Ion concentrations in typical brewing waters (Maltman 2003)

All rainwater is soft, it is in the water reservoirs it acquires its hardness. The longer the water spends in rivers, lochs or underground aquifers, the more time it has to gain solubles from the ground. The geology also plays a significant part, as hard granite or quartz is less soluble than limestone or chalk and very different from young basalt. 

Spring	Burn/River	Loch	Well	Mains
Ardmore	Aberfeldy	Ardbeg	Auchroisk	Devanha
Balvenie	Aberlour	Auchentoshan	Glenlivet	Dundashill
Benriach	Allt-a-bhainne	Bruichladdich	Macallan	Oban
Benromach	Aultmore	Cambus	St Magdalene	Strathdee
Cardhu	Balblair	Cameronbridge	Saucel
Convalmore	Balmenach	Caol Ila	Strathisla
Craigellachie	Benrinnes	Port Dundas
Edradour	Bladnoch	Millburn
Fettercairn	Blair Athol	Garnheath
Glenallachie	Bowmore	Glen Flagler
Glenburngie	Braes	Islabrae
Glencadam	Brora	Killyloch
Glendullan	Bunnahabhain	Kinclaith
Glen Elgin	Caledonian	Nort Port
Glenfarclas	Caperdonich	Port Ellen
Glenfiddich	Clynelish	Provanmill
Glen Garioch	Cragganmore	Pulteney
Glenglassaugh	Daftmill	Riechlachan
Glen Grant	Dailuaine	Rosebank
Glenkinchie	Dallas Dhu	Springbank
Glenmorangie	Dalmore	Longrow
Highland Park	Dalwhinnie	Springside
Longmorn	Deanston	Strathclyde
Mortlach	Glen Albyn	Tobermory
Pittyvaich	Glendronach
Royal Lochnagar	Glen Esk
Strathmill	Glengoyne
Tamdhu	Glenlochy
Tamnavulin	Glenlossie
Teaninich	Glen Mhor
Tomintoul	Glen Moray
	Lochside
	Macduff
	Mannochmore
	Man O'Hoy
	Miltonduff
	Royal Brackla
	Scapa
	Speyburn
	Talisker
	Tomatin
	Tormore
	Tullibardine

Water sources for mashing, hard waters in bold (Modified from Udo, 2006)

Scotland is divided into various different geological areas basically by several southwest-northeast-lines as illustrated below.

Geological map of Scotland (www.scottishgeology.com)

Speyside and the eastern part of Islay lie on the Dalradian rocks, formed about 570 million years ago and consisting mainly of metamorphosed sedimentary mudstone (schist and quartzite) with some granite hills. The rocks are old and resistant, therefore contributing little to the water, rendering it usually very soft, slightly alkaline and low sulphur. Notable exceptions are Glenlivet and Aberlour, which lie on top of granite-rich soil containing some limestone, rendering the water somewhat harder, especially from wells. 

Geology of River Spey (www.snh.org.uk)

The Moray Firth at the Great Glen Fault there is essentially a river delta with mud and sand carried by the rivers, consisting of especially old red sandstone. The red colour comes mainly from iron, but the porous sandstone is also rich in calcium and magnesium, rendering the water in the Northern Highlands and Orkney significantly harder than in the Speyside. The water of Islay lies somewhere in between.

Typical waters from Scotland (UisgeSource)

Several American distillers believe in hard, low-iron water

However, many distilleries do process the waters they use. Apparently all the distilleries use at least ion-exchange methods for their bottling (dilution) water, but not necessarily for the reduction right after distilling (to bring the new make spirit down to 63.4% abv). None use chlorinated water for mashing or dilution nowadays. In the earlier part of the 20th century local bottling water was used and there were complaints that London water turned the whisky blue and cloudy whereas Speyside water did not, probably due to harder water of London. Although there are several breweries applying reverse osmosis (demineralization) and specifically mineralized (Burtonized) waters, these methods are not used in the distilling industry, or at least they are not made public. Water softening with resins is not used, and it could be detrimental because it tends to increase the sodium levels. Grain distilleries might benefit from hard water, as the calcium induces enzyme activity and lower malt contents and faster fermentations could be possible, although it is not entirely clear whether the mineralization of mashing waters is allowed by the law and the Scotch Whisky Association.

So, fermentation waters affect the quality of mash. The minerals themselves do not significantly distill into the spirit, but they affect the fermentation process before it. Soft water probably produces more faster fermentations and lactic acid bacteria growth generally resulting in heavier spirits, as the harder Highland waters produce cleaner and sweeter spirits. Iron is considered as a fault in brewing water and it is likely to produce less estery, fruity spirits. Zinc might do the same at higher concentrations, but is vital for yeast cells in lower concentrations. Peaty water does not provide enough phenols to render the spirit peaty, but higher amount of organics in the fermentation water does produce more esters and less higher alcohols, probably due to greater bacterial growth and yeast autolysis. Fermentation water quality is important to the quality of whisky, but in a different way it has been marketed.

Effect of brewing water to the spirit sensory quality (Wilson, 2010)

REFERENCES AND FURTHER READING
Cribb, S&J. Whisky on the rocks. Earthwise, 1998
Geikie, A. The Scenery of Scotland viewed in connection with its Physical Geology. Macmillan 1887.
Goldamer, T. Brewer's handbook. Apex, 2008
Maltman, A. Wine, beer and whisky: The role of geology. GeologyToday 2003;19;1;22-29
Palmer, J & Kaminski, C. Water, a comprehensive guide for brewers. Brewers Assoc., 2013
Scottish Natural Heritage. http://www.snh.org.uk/pdfs/consults/spey/speyreport.pdf

Wilson, CA et al. The role of water composition on malt spirit quality. 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.

Sulphur

Sulphur candle

Sulphury notes are a controversial part of whisky aroma. Individual differences in perceiving the sulphury flavours seem to be great and easily arguable. Sulphur in its natural S8-form is quite stable with an odor of matchsticks. Most organic sulphur compounds however have usually very low perception tresholds and pungent odors. Organic sulphur compounds have been associated with meaty, burnt, rubbery, rotten aromas, but also some unexpected aromas such as grapefruit. Often low levels of sulphur are associated with mature, rancio, complex and meaty notes in whisky.

Sulphur in the whisky is mostly sourced from the aminoacids of the grains used in fermentation. The barley used in the whisky production are usually spring varieties and typically very low in protein and thus low on sulphury aminoacids (cysteine, methionine), too. However the yeasts metabolise the available aminoacids and in the process produce a variety of organic sulphur compounds. Typical byproduct of anaerobic sulphur metabolism is hydrogen sulphide (H2S), which has a strong unpleasant odor of rotten eggs and can further metabolise into thiols and other organic sulphur compounds. Excess amounts of yeast or the use of brewer's yeast or long fermentation times tend to increase the autolysis of yeasts and therefore add to the sulphur content of the wash. The lactic acid bacteriae can produce sulphury compounds, especially Lactobacillus brevis tends to impart a sulphury aroma.

Some sulphur is used during the kilning process, especially if peat is used to dry the grains. The anaerobic bacteriae in a peat bog produce sulphury compounds and obnoxious nitrosamines and by burning some sulphur with the peat the off-notes (and toxins) can be converted mainly to sulphur oxides, which do not spoil the grain.

The copper used in the distillation stills reduces the sulphury content of the whisky most likely by acting as a catalyst in processes resulting in insoluble copper sulphates. On the other hand copper has been associated with an increase in some sulphur compounds in the spirit, such as dimethylsulphate (DMS). Low copper contact (small/squat stills), fast distillation and high temperatures increase sulphury notes on new make spirit. Direct heating probably increases sulphury notes as there is bound to be some burning of grains at the bottom of the still and temperature variations between different parts of the still.

Cask maturation significantly reduces the amount of most sulphur compounds in the whisky, even so that in a recent study all of the dimethyl sulphide (DMS), 3-methylthiolpropylacetate, dihydro-2-methyl-3(2H)-thiophene and ethyl-3-methylthiol-propanoate had disappered after 3 years of oak maturation. Most organic sulphur compounds such as DMS decrease gradually during aging. This is most likely due to evaporation and to a lesser degree to oxidation or reactions with the carbon layer of the charred cask.

Key sulphur compounds in new-make spirits and single malt whiskies (Masuda & Nishimura 1982)

The individual perception of different sulphury compounds appears to be very different. As experienced tasters rated different sulphur compounds (in a study by Jack FR et al 2008), there was considerable variation between individuals and compound.

Sulphury character of different sulphur compounds, modified from Jack et al 2008

The most perceived MMFDS and 2-thiophene-cis-aldehyde, 4-methyl-thiazole, 4-methyl-5-vinyl-thiazole as sulphury and the mix of all was statistically the most sulphury of them all. At least one taster did rate the sulphury taste less than 1 out of 10 for all but two compounds. Several tasters were non-tasters for some compounds that the others rated highly sulphury. It is to be noted that all but one tasters rated one individual compound more sulphury than the mix of all, so the sulphury taste is not an add-on characteristic but rather a combination. For example 2-pentyl furan distictively suppresses the sulphury character of DMTS, just like salt suppresses a bitter taste (just try a tiny amount of salt in your coffee).

Sulphury character of different sulphur compounds, modified from Jack et al 2008

However, there has been controversy about sulphury casks in the whisky industry. Especially Jim Murray, the author of The Whisky Bible has been worried about sherry cask-derived sulphur-taints. Sulphur is widely used in wine industry to prevent bacterial growth in must and to improve the stability of wine. It is usually used in the form of sulphur dioxide, usually soluted in to a liquid form for ease of use. Sulphur dioxide acts as an antioxidant and antibacterial agent in wines. Excess sulphur dioxide content may intensify some allergic reaction and impart off-notes into wine. Sulphur candles or brimstone sticks have been used to preserve casked wine and to prevent bacterial contamination of casks stored empty.

Fumigation of casks with sulphur has been used probably from the Roman era. The use of sulphur matches and candles for preserving wines and other perishables was common in late 18th century Europe. Wine writer André Jullien describes the fumigation of wine casks in 1825:

"Fumigating wines is impregnating them with sulphurous vapours, obtained by the burning of brimstone matches... aromatics are often mixed with the brimstone... the Strasbourg [violet scented matches] are to be preferred for wine... When old wine runs clear, it is sufficient to burn a bit of match in the cask you are going to fill. To hasten the fermentation of new wine, burn several matches and shake the wine in the vapour... Many vineyards produce wines of a sulphurous taste, which goes off in time" (as cask maturation/storing was common at the time). This practice reduced the oxygen in the cask and prevented lactic bacterial brettanomyces contamination, therefore enhancing the stability and quality of wine.

Sulphur burners are still used
by amateur winemakers.

There are many references from the 1700s and the 1800s describing different cask sulphuring methods. Usually sulphur was introduced into the cask through the bunghole in a wire containing a linen cloth, which had been coated with sulphur. The cloth was burned and the bung closed, resulting in oxygen-deprived cask with some sulphur dioxide and some sulphur trioxide gasses. A fresh cask usually used first for fermentation was considered quite clean, so they were only slightly or not at all sulphured. Sulphur dusting of the vines was used as a cure against oidium (powdery mildew), the first of the fungal diseases from America, in the 1850s.

The effects of sulphur in casks were not completely understood and in 1873 there was a scandal in Britain, as Dr Thudicum wrote that the sulphuring, plastering (adding calciumcarbonite into must) and fortification of sherry was to be considered as adulteration and that the sherry wines were inferior to the French wines and probably dangerous to health. The fact that also the French were sulphuring their casks was not discussed and there were probably some trade-oriented motives behind the argument.

Different types of sulphur used in winemaking

Adding sulphur dioxide into wine has been common from at least the 1890s. It prevents bacterial and wild yeast growth and acts as an antioxidant preventing overoxidation and browning. During early 1900s some wineries used (hugely) excess sulphur dioxide in order to use bigger tanks and less strict oxygen control, but it resulted in sulphur tainted wines with overly "reduced" aromas. Sulphur dioxide content is limited by EU under 160mg/l in red wines, 210mg/l in whites and 400mg/l in sweet wines. Most wineries use concentrations below 100mg/l, but non-sulphured commercial wines are rare as they easily become oxidized. Sulphur dioxide was obtained by burning sulphur candles in the late 19th century, but since the early 1900s it has been mostly used in liquid form or as potassium metabisulphite; Californian wine expert Maynard Amerine stated already in 1970 that no burned sulphur is commonly used in wine making anymore, and there is no evidence that the major sherry cask suppliers or whisky distillers had used sulphur candles for several decades. Theoretically excess sulphur dropped from a candle might be reduced to H2S or mercaptans by yeasts producing sulphury off-notes.

Since 1986 Spain has been a member of EEC and the shipment of sherry has been made very hard by the Denominacion de Origen to encourage bottling in Spain. Bottling of sherry is done almost exclusively in Spain and full sherry casks are no longer imported. The sherry shippers had already started their own bottling plants in Spain in the early 20th century. Pedro Domecq started their bottling operations in Jerez in 1920 and Gonzalez Byass was to follow gradually during the interwar period. Sandeman bottled some of their sherries and ports in location as early as 1880, but the bottling of sherry in England by Sandeman ceased in 1969. Harvey's were the last big shipper to bottle their sherries in England, as they bought a winery in Jerez from MacKenzie in 1970 and since then have been bottling practically all of their sherries in Spain. Therefore since early 1970s many distillers have been maturing whisky in sherry casks made to order in Spain. Both American and Spanish oak casks are coopered and usually the sherry used in seasoning is oloroso, but sometimes lower quality blending sherry called raya, which resembles oloroso. Some bodegas, for example Gonzalez Byass and Pedro Romero trade their old empty solera casks, which are made exclusively of American oak and usually 80-100 years old and probably very different from a typical sherry shipping cask or a seasoned cask. Another quite popular way of producing sherry casks was to rejuvenate old exhausted cask by scraping the inner surface, toasting it again and seasoning it with sherry. Aeriation of whisky, during bottle maturation or in greater extent after the bottle has been opened, usually decreases the highly volatile sulphury notes.

In conclusion, there is good and bad sulphur in whisky. To simply pin one or two sulphur compounds responsible of the good or the bad aromas would be an oversimplification. Similarily the origins of sulphury notes seem to be impossible to track to just one source, such as sulphury cask and there is no evidence of excess use of sulphur candles in the sherry industry during the last decades, in fact quite the opposite. More likely is that there are some bad batches distilled too fast or in too warm climate that are over-sulphury, or maybe a cask has not been properly sulphured and has been contaminated with brettanomyces.

REFERENCES AND FURTHER READING
Harrison, B et al. Impact of copper in different parts of malt whisky pot stills on new make spirit composition and aroma. J Inst Brew, 2001;117(1);106-112
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.
Jack, FR. Understanding Scotch whisky flavour. Food Sci Tech 2003;14;28-30
Jullien, A. Wine merchant's companion and butler's manual. 1825
Labuza, T et al. Maillard reactions in chemistry, food and health. RSC 1994.
Masuda, M and Nishimura, K. Changes in volatile sulfur compounds of whisky during aging. J Food Sci 1982; 47(1); 101-5
Reaich, D. Influence of copper on malt whisky character. In Proceedings of 5th Aviemore Conference on malting, brewing & distilling. 1998
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