Scottish whisky mash bill

Malted barley is the main ingredient in Scotch malt whisky. Barley (Hordeum) is a member of grass family, just like most cereals in the world. There are two main types of barley: two-row and six-row. Both have six rows of seeds, but in the two-row varieties only two are fertile. The two-row varieties have usually plumper grains, less protein and husks and more fermentable sugars than the six-row varieties. The British malting barley varieties are and were almost exclusively of the two-rowed type, and the protein-rich six-row barley is mostly used for cattle feed. Barley can be sowed during the winter or in the spring, depending on the variety and the climate. Most distilling malts are made of spring barley, because they malt better with less dormancy issues. European brewers mostly use two-rowed barley, while Americans utilize mostly 6-rowed. Some varieties are naked, ie they do not have so much husks.

During the 17th and 18th century the main cereals grown in Scotland were barley, oats and rye. It is likely that all of them were used to produce distilled spirits (and whisky), although barley was probably favoured for its better enzyme activity. Additionally oats had too much husk for efficient mashing and rye tended to produce excess yeast growth. Mixed fermentations were probably often used, after all distilling was merely a way to preserve excess crop. Martin Martin in 1702 describes the practice on the Isle of Lewis: "The corn grown here is barley, oats and rye... Natives brew several sorts of liquors; as common Uisquebaugh, another called Trestarig, id est Aqua Vitae, three times distilled, which is strong and hot; a third sort is four times distilled Uisquebaugh-baul; id est Uisquebaugh...The Trestarig and Uisquebaugh-baul are made of oats". The oats were likely to produce a wash lower in alcohol and higher in congeners, so the process of three or four distillations makes sense. Multiple distillations and narrower cuts were most likely used to produce a palatable spirit, not so much to reach high alcohol strengths.

Chevallier barley was recently revived in Norwich by Dr Chris Ridout

During the 18th and 19th century the barley varieties used were local landraces, which were selected by the local farmers. In Scotland local landraces, probably most of the variations of Scotch Common, a two-row, narrow-eared, small-grained, early ripening variety, dominated until the 19th century. In colder climates, especially in the Northern Highlands some bere barley, a six-rowed landrace, was cultivated, but it was mostly used as cattle-feed. Most early 19th century English landrace varieties were probably close to Czech Hanna variety, a two-row, early ripening barley with a quite brittle straw. First generally successful variety in Britain was Cheval(l)ier, discovered in Suffolk, 1819. It spread across the country quite rapidly and most of the barley sown in the 1840's Britain was Chevalier, especially in the South. The other widely spread variety in England was Annat (1830) and in Scotland some of the Hanna varieties were still used in the late 19th century.

The price of maize and grain whisky (Weir 1995)

Malted barley was the main ingredient in both pot-still and column still whiskies in the 1830-40s, although column distillers began adding unmalted barley into the mash. In 1848 adjuncts, such as molasses, treacle and sugar were permitted in whisky production (1847 for beer) and further tax cuts made it possible for especially column distillers to produce whisky from a variety of  raw materials, mainly from cheap American maize. Maize was about 30% cheaper than barley at the time and as the production in the USA increased during late 19th century, it quickly became the major ingredient of column still whisky. By 1877 the average grain whisky mash-bill was: maize 77%, barley 20%,oats 2,5%, wheat 0,4%, rye 0,02%, malted barley 0,14%. The grain for column distillers was bought predominantly from abroad, less than 1% of the total grains and 2-6% of the barley were sourced from UK at the time. Oats, rich in fibers, were in mainly to improve the draining. The role of rye was to propagate yeast, while barley provided the enzymes. The cheap maize, efficient continuous Coffey still and the crisis in wine/cognac industry helped the boom of grain whisky in late 19th century. Brewers turned to foreign barley in the late 19th century mainly because of better quality of the Danish malt, not so much for the price. The  Irish distillers used a mixed grain bill from the late 19th century, usually consisting of barley malt (30-50%), unmalted barley (30-40%), oats (20-30%), rye (3-6%) and wheat (5-10%).

The pot-still malt whisky distillers were more traditional, even superstitious in their grain purchases compared to brewers and grain distillers. They used mostly local barley throughout the 19th century, although during the periods of bad harvests and/or higher whisky demands, as during the 1890's whisky boom, they were forced to use some foreign barley, mostly from Denmark, the Baltic and Morocco. There were other significant reasons for pot distillers to use local barley: They were trying to ban the grain distillers from marketing grain spirits as whisky or Scotch and proposed that only whisky made from Scottish grain could be called Scotch. The local farmers also bought much of the draff (waste product of the first distillation, great cattle feed) from the distilleries, so both benefited from direct sales to each other without any mediators. One likely explanation for the local sourcing of barley is the traditional and frankly sometimes superstitious approach on any improvement or change of the process or the product.

Beaven 1947

In the beginning of 20th century the predominant varieties were Annat, Goldthorpe, Archer, Spratt and Chevallier. After the World War I hybrid selections began to be made. Spratt-Archer and Plumage-Archer were popular and together comprised of 80% of malting barley until the World War II. The selections were made mostly based on the yield per acreage and the carbohydrate yield of the malt, flavour was rarely discussed. The foreign barley entered the distilling malt markets in 1920s, sourced mainly from Denmark and Chile (probably 6-rowed), and to some extent from Romania, Tunisia, Canada and Australia. Danish and Australian were preferred of for their quality, but for trade protectionist reasons the distillers (lead by DCL) agreed to by preferentially Scottish and English barley.

In the 1920s the prices of cereals varied widely and grain whisky was made from various ingredients based on the world market. Barley from California and Canada (small 6-row), maize from US and Argentina, oats from Scotland and Canada, even Brazilian manioc were used. The column grain distillers used the cheapest available raw materials, for example the maize bought from USA was usually grade 3, while the US domestic distillers used grade 1-2 maize.

During the WW II, Danish Kenia was grown widely for its better yields, however it was not good for malting and after WW II Pioneer (Kenia x Austrian Tshermarks) and Proctor (Plumage-Archer x Kenia) dominated until 1960 with a acreage up to 70%, although DCL seems to have preferred Zephyr. Due to rapid growth in whisky production in the 1950s, more English and foreign barley was used. If six-row barley was used, the smaller grains were sold to the distillers (more enzymes) and the plumper grain (more yield) to the brewers. Golden Promise and Maris Otter were introduced in 1965. Golden Promise became the barley of choice for distillers for its yield and enzyme activity until 1980s and Maris Otter was the brewers' malt, allegedly for its flavour. In the 1980s German Triumph and its many hybrids (Corgi, Natasha, Optic, Prisma, Camarge) surpassed the Golden Promise for their better yield and some winter varieties were introduced in Southern Scotland (Melanie, Halcyon, Regina). After that many different varieties have been developed and the suitable varieties for distilling and brewing are declared annually by Institute of Brewing and Distilling.

Improvement of spirit yield (Russell, 2003)

Brookes 2005

During the 20th century the acreage yield of barley has increased rapidly. Archer gave less than 3 tonnes per hectare as modern barleys for distilling malt give up to over 8 tonnes per hectare. Also the alcohol yield has improved drastically, from 300 litres of pure alcohol per tonne of dry malt to about 460 lpa/t.

Recently old varieties have been revived, mostly due to growing craft beer movement, but also by some malt distilleries. Bere barley was used in whisky production in Highland Park until 1926 and has since been used mainly for bere bannocks, but also for malt whisky. Bere was 6-row barley variety originating probably from northern Scandinavia with long stem and rapid growth (therefore also called 90-day-barley). Michel Couvreur revived the bere whisky in 1985 when he used bere from Orkney to distill whisky at Edradour. Since then at least Arran, Springbank and Bruichladdich have released bere whisky.

Sadly, there are no scientific comparisons between the flavour of different barley varieties. The early malting varieties were proportionally higher in protein and fat but lower in carbohydrates. Steeping times were much longer, probably because lack of knowledge and to some extent because of dormancy-prone barley varieties. The germination times were longer and the temperatures in floor maltings were more uneven than in modern maltings. These differences most likely made the wort more prone to infections of wild yeast and lactobacilli, along with mostly longer fermentations and lower starting gravity. The consistency was probably more viscous due to greater proportion of betaglucans to alpha-amylases. So the wort was likely to have more husks, dead yeast, autolysis products, lactobacilli, oils, diacetyl, esters (from acids and alcohols) and thicker in consistency causing easier burning in the wash still. The result was likely to be oilier, more sulphury and fruity spirit with more higher alcohols (fusels) and more furfural (from the husks, providing nutty aroma), assuming that the other factors were kept constant. It is unlikely that there are considerable differences within the modern barley varieties in terms of distilling, since the specifications for malting barley are quite strict. However, there is proof that the change of barley variety also changes the lactobacilli flora in the distillery, which might have at least some effect to the spirit if long fermentation times are used. The practice of malting (floor malting/industrial malting) has probably greater effect on flavour than the barley variety.

Maize mill at Dumbarton (I.Hume)

Because the use of enzyme additions is prohibited in Scottish whisky, the grain distilleries continue to use about 10% of malted barley in their mashes to guarantee sufficient enzyme content for starch degradation. Maize from the USA dominated the Scotch grain whisky mash bill from 1860s until early 1980s, excluding the war years. Since then, wheat has surpassed it, mainly because the trade regulations and taxes, not so much because of the actual cost of raw materials. Actually the price of unmalted barley has been quite competitive against maize and wheat in recent decades, but the processing problems have steered most grain distillers to wheat, mainly from France in the 1980s, but lately predominantly from the UK, with a fraction imported from Germany and France. North British is the last Scottish distillery to use predominantly maize, as the other "maize distillery" Dumbarton was closed in 2002. Some maize is still used at least occasionally in most grain distilleries, most likely to minimize viscosity problems. Maize has lower viscosity of mash compared to wheat and malted barley, because of lower amounts of betaglucan and pentoses. Since 1990s the Scottish distillers' maize has been bought exclusively from southern France due to trade barriers of EU. Bakers and farmers prefer high nitrogen wheat, so there is not a serious competition over low-nitrogen grains and distillers' wheat does not carry a price premium.

Biernacka&Wardencki 2013

The differences between wheat and maize spirits are surprisingly clear, there are less differences between wheat, triticale and rye spirits. Maize spirits contain about ten times less higher alcohols than the other grain whiskies, but have proportionally higher levels of esters (fruity). The higher amount of pentoses in maize also contribute to the higher furfural (nutty) content. The greater variety and amount of higher alcohols in wheat spirit account to more harsh, spirity and solventy notes in young spirit, but a likely to develop to a variety of acetals and esters, with more fruity aromas. The popcorn aroma sometimes present in blended whisky is likely to come from too much feints from the malt whisky involved, not from the grain component. The mouthfeel of wheat whisky can be oilier or waxier due to more arabinoxylans, while corn whisky is usually described cleaner and shorter.

Biernacka&Wardencki 2013

REFERENCES
Agu RC et al. Production of grain whisky and ethanol from wheat, maize and other cereals. J Inst Brew 2006;112;4;314-323
Beal, AD & Mottram DS. Compounds contributing to the characteristic aroma of malted barley. J Agric Food Chem 1994;42;2880-4
Biernacka P & Wardencki W. Volatiole composition of raw spirits of different botanical origin. J Inst Brew 2012;118;393-400
Beaven, ES. Barley. Duckworth 1947
Briggs, D. Malts and Malting, Blackie 1998
Bringhurst TA. Barley research in realtion to Scotch whisky production. J Inst Brew 2015;1;1-18
Brookes, P. Barley Breeding and development in the UK, an historical perspective. Brew Hist 2005;121;25-39
Bryce JH et al (ed). Distilled spirits: Production, technology and innovation. Nottingham Univ Press 2008
Campbell I (ed). Proceedings of the Third Aviemore Conference on Malting, Brewing and Distilling. Intitute of brewing, 1990.
Collins TS et al. Profiling of nonvolatiles in whiskeys. Food Chem 2014;163;186-196
Cramer ACJ et al. Analysis of volatile compounds from various types of barley cultivars. J Agric Food Chem 2005;53;7526-31
Dong L et al. Characterization of volatile aroma compounds in different brewing barley cultivars. Sci Food Agr 2014
Hoff S et al. Influence of barley varieties on wort quality and performance. J Agric Food Chem 2013;61;1968-76
Hornsey, IS. A History of Beer and Brewing. Royal Society of Chemistry 2003
Lloyd, WJW. Adjuncts. Centenary review. J Inst Brew 1986;92;336-345
Mallett, J. Malt. Brewer's Publications 2014.
Martin, M. A description of the Western Isles. 1702
Martin, P & Chang, X. Bere whisky- rediscovering the spirit of an old barley. Brew Dist Int 2008/4;6;41-43
Mather, RT & Willkie, RT. Distillers' grain manual. Seagram, 1942
Piggott JR et al (ed). The science and technology of whiskies. Longman 1989
Priest, FG & Campbell I (ed). Current developments in brewing and distilling. Aviemore conference 1982.
Robson, F. Cameronbridge, a distilling giant. Brewer Int 2001;1;4;16-19
Russell I (ed). Whisky, technology, production and marketing. Academic Press 2003
Weir, RB. History of the Distillers Company 1877-1939. Oxford 1995.

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
www.practicalwinery.com/janfeb09/page1.htm

http://www.smws.co.uk/your-society-adventure/article-archive/A_matter_of_taste.html

Lactic acid bacteria

Lactic acid bacteria (LAB) are a diverse group of bacteria capable of lactic acid production. They are found for example in cheeses, yoghurts or decomposing plants. They are non-respiratory (anaerobic), but tolerate also aeriated environments and can survive high acid (pH 3-6) and high ethanol concentrations. The Lactobacillales can be divided into different genera, such as Lactobacillus, Leuconostoc, Pediococcus, Lactococcus and Streptococcus etc. Of these the Lactobacillus and in lesser extent the Pediococcus are dominant in distillery environment, although many others survive alongside them. The LAB are present in small quantities in the raw materials, especially the grain, but generally the contamination of wort with LAB comes from the distillery environment (pipes, washbacks etc) and therefore the LAB population in whisky distilleries remains quite stable and the dominant strains of LAB are practically unique in any one distillery.

The yeast dominates the early fermentation and LAB starts to grow significantly after about 36-48 hours as the yeast starts to drop out or die. At the start of the fermentation there are usually various types of LAB in the wort, but many of them die out as the ethanol concentration rises. The first LAB to grow are usually heterofermentative ie they metabolise sugars into lactate, acetate and CO2, the most common species being L.fermentum, L.paracasei and L.brevis. The homofermentative LAB, such as L.acidophilus and L.delbrueckii, producing only lactate from sugars appear later after about 70 hours of fermentation.

Microbes in whisky fermentation, MB-stained=dying cells (Priest 2004)

The heterofermenting LAB can also use pentose sugars, which the Saccharomyces cerevisiae can not ferment, so they are not necessarily competitive. The homofermenters use only hexoses and they always reduce the spirit yield a bit, although they can also use the autolysis products of the dying yeast for their metabolism. The usual amounts of LAB at the start of the fermentation (below 10^6 cells/ml) do not affect the spirit yield, but amounts greater than that could cut the yield up to 20%. The usual amount of LAB in the wort are usually 10^4 to 10^5 per millilitre and rise up to 10^9 at the end of a long fermentation.

Growth of lactic acid bacteria in whisky wort (van Beek 2000)

The effect of LAB on the flavour profile of whisky depends on the species and even the strain of the LAB. Also the availability of metabolites via yeast cell death affects the flavour profile. Probably the most important and common effect of LAB is the increase of lactic and acetic acid, which together with sufficient amount of alcohols leads to increased levels of esters. The lower pH also affects the volatility and activity of various aroma compounds during fermentation and distillation.

The yeast cell death allows the LAB to metabolise the autolysis products, for example the cell membranes containing lots of fatty acids. The LAB hydroxylate these fatty acids into gamma- and delta-lactones, especially gammadecalactone and gammadodecalactone, which produce a heavy sweet and fatty aroma also found in tropical fruits (apricot, peach). The use of brewer's yeast in the fermentation leads to faster yeast cell death and subsequently to higher levels of gammalactones with sweet and fatty notes.

The LAB can alter phenolic aromas as they can decarboxylate cinnamic acids to 4-vinyl guaiacol or 4-vinylphenol and further to 4-ethylphenol. Ferulic acid and p-coumaric acid are common cinnamic acids in malted barley and a typical distiller's yeast (DCL M) and most wild yeasts, but not most brewer's yeasts, can decarboxylate them into 4-vinylguaiacols (smoky, spicy, clove). The LAB has the same decarboxylation enzyme, but they can reduce 4-vinylguaiacol further to 4-ethylphenol (guaiacol, barn-yard, band-aid, brettanomyces), which usually softens the smoky aroma. The smoky aromas are dimished especially if the fermentation is allowed to continue longer.

Amounts of guaiacols in whisky fermentation with DCL M+LAB (Van Beek 2000)

	fruity	fatty	green	sweet	sour	sulphury	meaty
L.paracasei	+		+		+
L.plantarum	+		+		-
L.brevis	(-)	+	(-)	++		++	++
L.casei	+	+
L.fermentum	+	+	+
L.acidophilus		+	+
T.delbrueckii (wild yeast)	-	(+)	+	+	-	(-)	+/-

Some effects of LAB and wild yeast on the flavour of new-make spirit (Van beek 2002, Priest 2004, Wilson 2008)

The growth of LAB depends heavily on the cleanliness of the distillery. Most of the LAB from the raw materials die during the malting and mashing and the main source for the LAB is from the pipes and the washbacks. Steel washbacks are easier to clean and probably lead to lower and different LAB colonies in a distillery. Long fermentation times increase the LAB growth, especially after 48 hours. Some distilleries have variable fermentation times, for example shorter during the week and longer over the weekend, which tends to produce slightly different wash profiles. Below is a table about different distillery fermentation practices.

Distillery fermentation times and washback materials (Udo 2006)

Variable fermentation times (usually weekdays/weekends)

REFERENCES AND FURTHER READING:
Booysen C et al. Isolation, identification and changes in the composition of lactic acid bacteria during the malting of two different barley cultivars. Int J Food Microb 2002;76;63-73
Bryce JH et al (ed). Distilled spirits: Production, technology and innovation. Nottingham Univ Press 2008
Simpson KL et al. Characterization of lactobacilli from Scotch malt whisky distilleries and description of L.ferintoshensis. Microb 2001;147;1007-1016
Smit G., et al. Flavour formation of lactic acid bacteria and biochemical flavour profiling of cheese products. FEMS Microb rev 2005;29(3);591-610
Udo M. The Scottish Whisky Distilleries. Black & White 2006
van Beek S, Priest FG. Evolution of the lactic acid bacterial community during whisky fermentation. Appl Microb 2002;68(1);297-305
van Beek S, Priest FG. Decarboxylation of substituted cinnamic aceds by lactic acid bacteria isolated during malt whisky fermentation. Appl Envir microb 2000;66(12);5322-5328
Walker GM, Hughes PS (ed). Distilled spirits, new horizons: energy, environment and enlightenment. Nottingham Univ Press, 2010
Wilson NR. The effect of lactic acid bacteria on congener composition and sensory characteristics of Scotch malt whisky. Thesis Heriot-Watt Univ 2008.