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

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

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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