Sugars in whisky

There are small amounts of sugar in all whiskies. Scottish whiskies have some sugars dissolved from the oak cask and often some from optional caramel colouring (E150a). Total amount of sugars is quite low, usually well below 1 g/l, but in certain cases it is quite possible to reach a few grams per liter. The sweet aromas of whisky matured in refill bourbon or new oak casks mostly come from sweet aromatic vanillin and fruity esters, not from the sugars. However, sugars can have a significant role in the case of casks previously used for sweet wine or sweetened spirit.

Typical composition of a liquid E150a colouring

Sugar gets to whisky from the oak cask used in maturation and its possible previous contents, especially sweet wine, and often from optional caramel colouring. New make spirit does not contain significant amounts of any sugars and it is not legal to add sweeteners to Scottish whisky, Irish whisky or bourbon, unlike to most rums, other American whiskies, Canadian whiskies, cognac, armagnac, vodka and so on. However, caramel colouring is an allowed additive in Scotch whisky. The E150a colouring used in whiskies consists of mostly of water (30-50%), carbohydrates (50-70%) and ash (0-4%), depending on the manufacturer. The colour comes mostly from furans and furfurals, mainly 5-hydroxymethylfurfural (5-HMF). The carbohydrate composition varies a lot, but usually the amount of simple sugars (mono- and disaccharides) is about 10-20% of the total volume and about 20-40% of the total carbohydrates. Caramel colouring as such is not sweet but rather bitter, although it probably enchances the perception of vanillin and some other sweet notes while supressing some sulphury notes. The amount of caramel added to whisky is usually well below 1 g/l, but there is no legal upper limit, although 2g/l of E150a (0,2-0,4 g/l simple sugars) would render the whisky very dark. In one independent study the highest caramel solids amount found in a Scotch whisky was 0.97-1.10 g/l (simple sugars ~0.2-0.4 g/l) depending on the analysis method (I suspect L*******g, but no names) and the average amount was 0.278 g/l caramel (from 0.01 to 1.10 g/l). According to Valaer in 1940 there was a legal maximum of one pint of liquid caramel per barrel of whisky permitted by the British Customs and Excise Regulations (0.15% or about 1.5 g/l).

Caramel content of various whiskies (Boscolo et al 2002)

Another source of sugars in whisky is wood. Oak is composed of three main macromolecules; cellulose is a long-chain D-glucose-fiber. Hemicellulose is a mesh-like branched chain of 5-carbon sugars (xylose, arabinose, galactose, ribose, rhamnose) and glucose. Lignin is a complex matrix of polypropane and polyphenols. Cellulose breaks down very slowly in alcohol-water solution extracting very small amounts of glucose to whisky. Most sugars extracted from the cask come from hemicellulose, hence most of them are 5-carbon sugars. Arabinose, xylose and rhamnose taste about half as sweet as glucose, where as fructose is almost twice as sweet compared to glucose.

About 100 mg/l of solids (including sugars) is extracted from new charred oak casks during the first year of bourbon maturation and after 1-3 years typically significantly less and only as little as 4 mg/l/year extraction has been reported from old refill casks used for example for cognac (or Scotch) maturation. A toasted cask extracts considerably more sugars compared to a charred cask, but typically about 150-250 mg/l/year is reached for the first year(s) of maturation. For comparison, a 40 years old brandy matured in a toasted oak cask had 2 g/l sugars (averaging 50 mg/l/year), while a 30 years old cognac (probably mostly matured in a refill casks) had only 0.5 g/l (17 mg/l/year).

Sugars dissolve in water better than in ethanol, so for example 55% ethanol-water solution can extract almost two times more sugars from the wood compared to 70% abv solution. The difference between 40% abv and 15% abv seems to be just about significant, so the alcohol strength is probably important only for high proof spirits. High entry proof is likely to significantly diminish the sugar extraction. Toasting and especially charring of the oak lowers the amount of extractable sugars, converting them to for example furfurals ("caramel"). On the other hand, charring contributes to sweetness by increasing the formation, extraction and perception of other sweet-tasting compounds, especially vanillin.

Analysis of different spirits by GC-MS (Savchuk 2001) Note the high levels of vanillin from new charred casks.

Probably the most important factor considering the amount of sugars in Scotch is the previous content of the cask. The most usual type of cask, the ex-bourbon cask would impart minimal amounts of sugars, often well under 50 mg/l/year and overall well below 1 g/l even during a long maturation, usually in the range of few hundreds of milligrams per liter. The charred American oak cask used for bourbon is quite low on sugars to start with and the bourbon will extract a major part of the available sugars. A toasted cask previously used for cognac, armagnac, brandy of other non-sugared spirit could extract slightly more, but most likely still not over amounts 1 g/l during refill maturation.

Venezuelan rum, 40 g/l sugars

Rum can, and often does, contain added sugar or other sweeteners. Most sweetened rums are sugared at the bottling phase, but sometimes sugar (or molasses, cane juice, fruit etc) has been added already into the cask and some of that sugar is bound to get into a ex-rum refill Scotch. Up to 40 g/l sugar contents are commonly reported in rum (100 g/l in spiced rums), but the amount of sugar added directly to cask is likely to be in the range of 5-20 g/l.

Pedro Ximenez sherry,
 470 g/l sugars

Significant amounts of sugar can be extracted from a sweet wine cask. Sherry is by far the most used ex-wine cask in the Scottish whisky industry. Most sherries, such as fino, manzanilla, amontillado, palo cortado and most olorosos, are dry wines (0-5 g/l sugars) and add only little sugars to the cask, some might even extract more than impart. Most sweet blended sherries (cream, dulce, sweet olorosos) are often blended with sweet must prior to bottling, not in maturation casks. The sweetness perceived in the olorosos often comes from high amounts of glycerol, not as much from sugars. A notable exception is Pedro Ximenez wine, which nowadays is vinified almost exclusively in Montilla-Moriles. It is a sweet wine produced from late harvested dried PX grapes and it typically contains by law over 212 g/l sugars. It is quite sweet even compared to other sweet wines, such as port (usually 100-150 g/l), Sauternes (100-200 g/l), Tokaji (60-500 g/l) or icewine (180-320 g/l).

The Scotch whisky industry has preferred sweet sherries for seasoning of their whisky casks from the 19th century and while most modern sherries are quite dry, most ex-sherry whisky casks were used for (or seasoned with) sweet sherries. In the 1800s and the early 1900s sweet(ened) sherries were imported to Britain in shipping casks. Britain was a major importer of sherry and emptied shipping casks were often used for maturation of Scotch whisky. By the late 19th century sherry casks were used extensively in Scotland and the first attempts to rejuvenate or season used casks were made in the 1890s. After the sherry casks were used for Scotch whisky maturation, they were seasoned with sweet sherry or paxarette, sometimes using pressure to soak the wood with the wine. By the early 20th century the use of sherry casks was quite wide spread, for example in the late 1920s a big whisky blender Johnnie Walker matured all of their whiskies in sherry casks or sherry-treated casks.

Aberlour 18yo
sugars <2 g/l

Shipping casks were mostly Spanish coopered lightly toasted American oak (Quercus alba) butts or puncheons (often called bocoyes in Spain). In 1972 Manuel González Gordon stated that "in recent years some Spanish oak has been used, due principally to the difficulties of importing American timber, but its greater density and hardness and lower porosity make it less suitable than the American wood". In the 19th century and the early 20th century they were often used for fermentation prior to shipping. Oak influence was not that detrimental for sherry during fermentation period and the fermentation process was believed to extract some of the excess tannins and bitterness from the wood prior the use in a solera or shipping.

The fermentation phase added plenty of sugars to the oak. For example, a typical 1980s (arguably Spanish oak, but at least Spanish coopered oak) shipping cask previously used for fermentation extracted 2.25 g/l sugars to whisky during only 6 years of maturation (375 mg/l/year). On the other hand an American ammonia-treated cask without a previous fermentation use would extract 770 mg/l (154 mg/l/year) sugars from a fino-seasoned cask and even less 655 mg/l (133g/l/year) from a similar oloroso cask. According to the table below, the previous use as a fermentation cask is very significant in the terms of sugar extraction.

JM Philp 1989

Ardbeg Dark Cove
4 g/l sugars

The most important factor considering the sugar extraction is probably the sweetest liquid to occupy the cask previously. According to Manuel González Gordon "large solera butts which have been used for years in a solera sometimes gain up to 25 kilos" in weight. In case of fermenting must or sweet wine, the refill cask can extract at least up to about 400 mg/l/year sugars. A typical sherry treatment used for Scotch whisky casks used in the 1890-1970s was made with about 35 litres of paxarette or sweet sherry per hogshead, but even with a relatively high pressure only a small part of the wine was absorbed into the cask. If we presume that as much as 5 litres of paxarette (375 g/l sugars) was absorbed into a hogshead and half of its sugars (just a figure from top of my hat) was extracted to the whisky, it would have resulted into 1875 g/ 220 litres = about 4.3 g/l of sugars, with a hypothetical gram or two from the cask itself could theoretically bring the sugar content up to 6 g/l during a very long maturation, say an average of 300 mg/l/year for 20 years. If were take a purely fictional solera butt used for an extremely sweet PX-wine (400 g/l) with 25 kg of PX wine absorbed into the cask and then used for whisky maturation, it could mean 10 kg of sugars in the cask and with a purely fictional extraction of about half of the sugars would result roughly to the amount of 9 g/l sugars into the whisky in an extreme(ly long) maturation from an extreme cask. It is probably safe to say that most spirits with over 10 g/l sugars contain additives and most spirits with over 2 g/l were matured in ex-sweet wine casks. Nowadays the sherry casks used in the whisky maturation are no longer used for fermentation or exposed to high-pressure paxarette/PX-treatment. The seasoning sherries are probably mostly medium oloroso/raya sherries with a sugar content in the range of 0-100 g/l, so a typical sugar extraction from that kind of cask could be in the range of 100-300 mg/l/year and diminishing through maturation, resulting to a maximum of a few g/l sugars into a modern whisky even during decades in a cask.

REFERENCES AND FURTHER READING:
Alañón ME et al. Monosaccharide anhydrides, new markers of toasted oak wood used for ageing wines and distillates. Food Chem 2010;119;505-512
Blanco Gomis D et al. Evolution of sugars in cider brandy aged in oak barrels, a contribution to its characterization. J Agric Food Chem 2003;51;923-926
Boscolo M et al. Spectrophotometric determination of caramel content in spirits aged in oak casks. J AOAC Int 2002;85(3);744-750
Boudet AM et al. Biochemistry and molecular biology of lignification. New Phytol 199;129;203-236
Clyne J et al. The effect of cask charring on Scotch whisky maturation. Int J Food Sci Tech 1993;28;69-81
González Gordon M, Sherry. Cassell Ltd 1972
Haldane FF. Casks; their manufacture and treatment. J Inst Brew 1906;12(7);688-711
Hills, P. Appreciating whisky. Collins 2000
Kansallisarkisto, Helsinki. http://www.arkisto.fi/en/the-national-archives-service/arkistolaitoksen-vaiheet-2 
Liebmann AJ & Rosenblatt M. Changes in whisky while maturing. Ind Eng Chem 1943;35(9);994-1002
Martínez Montero C. Estudio de parámetros alternativos como indicatores del envejecimiento y de la calidad del brandy de Jerez. Thesis, Universidad de Cádiz, 2006
Martínez Montero C et al. Sugar contents of brandy de Jerez during aging. J Agric Food Chem 2005;53;1058-1064

Mosedale, JR. Effects of oak wood on the maturation of alcoholic beverages with particular reference to whisky. Forestry 1995; 68; 3; 203-230
Mosedale JR & Puech JL. Wood maturation of distilled beverages. Trends Food Sci Tech 1998;9;95-101

Piggott JR et al. Effects on scotch whisky composition and flavour of maturation in oak casks with varying histories. Int J Food Sci Tech 1993;28;303-318
Piggott, JR et al(ed). The Science and technology of whiskies. Longman 1989

Read J. Sherry and the sherry bodegas. Sotheby's 1988
Savchuk SA et al. Application of Chromatography and Spectometry to the Authentication of Alcoholic Beverages. J Anal Chem 2001;56(3);246-264
Tolman LM & Trescot TC. A study of the methods for the determination of esters, aldehydes and furfural in whisky. J Am Chem Soc 1906;28(11);1619-1630
Tsai PJ et al. Interactive role of color and antioxidant capacity in caramels. Food Res Int 2009;42;380-386
Valaer P & Frazier WH. Changes in whisky stored for four years. Ind Eng Chem 1936;Jan;92-105
Valaer P. Scotch whisky. Ind Eng Chem 1940;32(7);935-943
Valaer P. Foreign and domestic Rum. Ind Eng Chem 1937;Sep;988-1001
Williams JF. Rapid determination of alcohol in distilled spirits and of color in whisky. Ind Eng Chem 1926;Aug;841-843

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
www.practicalwinery.com/janfeb09/page1.htm

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

Pajarete and the wine treatment

The ruins of Torre Pajarete
Castillo de Matrera, Villamartin, Andalucia, Spain
Foto www.laspain.com

Originally pajarete (paxarete, paxaret, paxarette, pacharetti) meant the Paxarete vineyards of Cartusian Convent of San Hieronomo near Jerez de la Frontera, probably east towards Villamartin and Prado del Rey. The vineyards were planted with sweet grape varieties Millar and Pedro Ximénez grapes along with some Moscatel and Palomino. After phylloxera there is no evidence of the dark and sweet Millar variety. Sherry wines called abocado, vino seco and paxarete were made in the monastery. The first grapes to ripen were picked first and set on esparto grass mats to dry. Palomino (Listán) was picked last and pressed usually on the same or the following day. The harvest lasted for 1-3 weeks allowing the Millar, PX and Moscatel grapes to dry longer, usually about 10 days. As a result the early ripening grapes became raisined and produced natural sweet wine of 8-15% abv and about 300-400 g/l of residual sugar, which was often fortified with brandy de Jerez. Abocado was a dry oloroso style oxidized sherry (sometimes sweetened with Palomino Dulce) and Vino Seco (or Fino Seco) a dry fino/amontillado wine, both of which could be still referred as (dry) Paxarete wines in the 19th century. Similar sweet wines were made in Rota from dried Tinta grapes producing bitter-sweet dark Tintilla de Rota. Color de Macetilla or Mistela was an oloroso, which had been fortified before it fermented completely, leaving it sweet, in the style of port wines. Another similar product was mosto apagado, which was done by adding sweet mosto into the wine producing partially fermented sweet wine and usually used only in blending of sweeter sherry styles. Dulce was made by fermenting must from (mostly palomino) grapes in a cask that contained brandy; the higher alcohol stopped the fermentation before all the sugar was used, producing sweet high-alcohol white wine.

Pedro Ximénez grapes dried on grass mats

The sweet paxarete was valued highly in Spain, but in the early 19th century Britain sweet sherries were considered more of a ladies drink, men preferring drier fortified wines, beer and spirits. During the 1830s the sherry trade boomed the first time and in 1838 there were 43 registered shippers of sherry. Paxarete was one of the most expensive types, costing up to 7 times more than the cheapest real Jerez sherry (probably raya) and usually a bit more than a good aged amontillado or fino. Sherry trade reached its peak of the 19th century in the 1870s as the French strugled with vine diseases. At the same time the branding and marketing of wines by the shippers really began, which made it easier to blend different wines to be sold as sherry, including those from different regions. Blending wines with mosto (grape juice), brandy, sugar and colourings was very common and not just in the sherry business. As dried grapes were easier to transport, some paxarete was often made from grapes imported from other areas. Málaga and Montilla became major producers of pajarete sherry in the late 19th century.

Malaga Pajarete from 1968,
Imported by the Finnish church
for sacramental wine

During the latter part of 19th century the English taste shifted towards lighter drier wines, partly because of the taxation and the flood of French wine into the market after 1860 as the customs embargo was dropped. Paxarete was still imported regularly and it was one of the most esteemed "malmsey" wines in Victorian Britain. Sherry barrels were used for whisky maturation probably from the early 19th century and as the blending and branding became common towards the end of the century. Sherry casks, and most likely also sherry as an additive, were used to give body to especially the lighter and younger grain spirits. Oxidized and sweet sherries such as pajaretes, olorosos, rayas and cream sherries were preferred because they gave the darkest colour and an agreeable flavour.

Pajarete was not a legally defined until 1999, so some producers from for example Málaga and California were selling pajarete/paxarete wines of their own, sometimes consisting of Pedro Ximénez wine, but quite commonly of caramel coloured, sweetened, oxidized and fortified wines. A notable imitation sherry was the very affordable Hamburg sherry, which consisted of potato spirit, caramel and spices. It was was banned in 1870 due to "health reasons". Most big sherry shippers had their own paxarete, PX or dulce brands; The Brown Bang Sherry (Sandeman), Gran Orden PX (Garvey's), Pio IX (Pedro Domecq), Delage Dulce, Osborne Paxarete and MacKenzie's Pajarete Solera. Some producers turned their raya wines (lower quality olorosos) into paxarete by maturing them outside in the sunshine, producing more cooked and concentrated wine. Vino de color, arrope or sanchoco were commonly used in blending of paxarete and cream sherries. Vino de color is any wine cooked and sometimes additionally sweetened with mosto. Sancocho is very sweet and concentrated wine boiled to one third of the original volume and arrope is thick syrup boiled to one fifth of the original volume. The tradition of boiling wines into syrups probably comes from the Moors, as they did not drink wine for religious reasons.

Arrope syrup

In the USA the boiled sweet fortified wine was classified as "Spanish-type blending sherry" by law in 1949 and manufactured mostly in California spesifically and exclusively for the whisky industry. The blending sherry was often sweetened with sugar or caramel, cooked to a reduction and infused with oak chips. It was not taxed nor was it possible to sell it as wine for consumers. Málaga and Montilla became the biggest producers of PX Pajarete wines in the 20th century Europe and Chile has its own DO Valle de Huasco producing pajarete wine. Cyprus made numerous bulk imitation sherries; the popular Cyprus Cream sherry was even sweeter than the natural paxaretes, probably due to added sugar. Imitation sherries were often colored with vino de color or caramel and fortified with industrial alcohol. The imitation sherries really stormed into the British market in the 1950s mainly in the lower price segment by agressive pricing.


Pajarete from Tarragona,
made of Moscatel and Garnacha

In 1999 Pajarete became a protected wine variety of DO Málaga and defined as "wine liquor, or natural sweet wine with a total sugar content of 45-140g/l produced without the addition of syrup [arrope], being aged and amber to dark amber in colour.". The Málaga pajarete is usually be made of Moscatel, but some Pedro Ximénez is also used. The pajarete style wines from Jerez are nowadays called PX, Pedro Ximénez, Moscatel or Dulce sherries and most of them are made according to the original soleo method.

Pajarete probably evolved from high quality sweet natural dessert wine to the blended, sweet(ened) and fortified bulk wine in the early 20th century. An affordable sweet brown sherry wine was just what the Scotch distillers were looking for, as it made possible the fast rejuvenation of whisky casks and enabled faster maturation.

WP Lowrie?

William Phaup Lowrie (1831-1916) pioneered the whisky cask management in the late 19h century. Lowrie was a merchant for both Port Ellen whiskies and González Gordon sherries, a cooper and later a co-founder of Glentauchers distillery. He was supposedly the first blender to use (sherry) wine finishes for whisky and the first cooper to import American pre-cut staves for UK cooperages. The brewers had used steam washers for new casks for decades. The process was automated already in the 1870s and it was common to use salt, hydrochloride acid, bisulphate or bicarbonate soda as additives when rinsing beer casks prior to refills. WP Lowrie introduced the steam pressure treatment to whisky industry primarily to test the integrity of casks in 1888, but soon after the steam was used also to remove harsh tannins from the fresh wood and to impregnate the wood with wine.

The wine-treatment of new casks became common in early 20th century and in 1929 it was reported that all of the new casks to be used for Johnnie Walker whiskies were seasoned with approximately 35 litres of sweet dark sherry per hogshead for 6 weeks. The casks were stored in an individual warehouse and turned regularly for even distribution of sherry into the wood. After the seasoning the casks were lightly pressurised ("with 0,2kg pressure", probably per one square inch?) and after that the remaining sherry was poured out. About 20% of the casks were said to be new, all of which apparently were UK-coopered wine-treated hogsheads made from import oak staves from the US or the Baltic. Older UK-coopered puncheons and Spanish-coopered butts were still being used as refill casks at the time.

The use of wine-treatment was introduced to save coopering costs and to ensure the availability of fresh casks as the sherry shippers had already started their own bottling plants in Spain in the early 20th century and the availability of home-emptied sherry casks was insufficient for whisky industry. Pedro Domecq started their bottling operations in Jerez in 1920 and González Byass were to follow gradually during the interwar period. Despite that, only 20 percent of sherry imports were in bottles during 1926-1940. Sandeman bottled some of their sherries and ports in location as early as 1880, but the bottling of sherry in UK by Sandeman ceased in 1969. Harvey's were the last big shipper to bottle all their sherries in England, as they bought a winery in Jerez from MacKenzie in 1970 and since then have been bottling all their sherries in Spain. In 1983 most (54.4%) of the sherries exported were bottled in Spain. The markets of EEC were easier to reach from Spain than from UK, especially after the preferential trade agreement with Spain and the EEC in 1970 and Spain's accession into EEC in 1986. Bottling of sherry is nowadays done almost exclusively (96.5% in 2000) in Spain and full sherry casks are no longer imported.

Harvey's bottling hall in the 1960s

As imported sherry casks became scarce due to the second World War in the 1940s and especially due to the increased bottling of sherry in Spain during the 1960s and early 1970s, the distillers rejuvenated the exhausted casks with pajarete. According to Philp in 1989 "a typical cooperage procedure was to add 500ml Paxarete per hogshead or 1 litre per butt, pressurise at 48 kPa / 7 psig for 10 minutes and then disgorge any absorbed paxarete.". Until 1972 the DCL also coopered their own sherry casks, which were made of American oak to a size of a puncheon (~558 l), wine-treated with paxarete and then used primarily for grain whiskies before used for malt whiskies. The American ex-bourbon barrels often received the same treatment; first fill with grain whisky, then after wine-treatment refilled with malt whisky.

Whether the Scotch distillers used real natural pajarete wine or sweetened imitations or even arrope or sancocho for seasoning is not clear, most likely they were not too fussy about the right provenance or traditional production methods concerning their "blending sherry". The typical seasoning paxarete of the 1980s was rich in tannins, esters and especially acids. A chemical analysis of different sherries by Philp in 1989 indicates that paxarette used at that point was very likely boiled and/or sweetened with arrope or sancocho as it contained 3,2 times more sugars (375 g/l), 5,7 times more tannins (4,7 g/l), 3,6 times more esters (278 g/l) and 6,9 times more acids (22 g/l) than an ordinary sweetened oloroso. In comparison the current version of Harvey's Bristol Cream has only 3,1 g/l acids and 130 g/l sugars and the naturally very sweet Don Guido 20yo PX sherry from Williams & Humbert has only 4,5 g/l acids despite of whopping 400 g/l sugars.

Photo: Albert Watson

As the Spanish sherry producers shifted from the traditional cask fermentations to use of modern steel tanks, the properties of casks changed. Fermentation was thought to remove many unwanted flavours from the fresh wood, especially bitter and sulphury off-notes. A special Gomez treatment was invented in the 1960s to simulate the effects of fermentation in the cask. It consisted of steaming the cask with ammonium hydroxide steam at 55 kPa (8 psig) for 60 minutes, which stripped much of the tannins and colour from the inner surface of the cask. This produced very neutral casks suitable for especially fino sherry maturation, but when subsequently used in Scotland they tended to produce light-coloured and slow maturing whiskies. The Gomez treatment was used from about 1965, but during the 1970s most of the Scotch distillers stopped buying these casks and began ordering their own spesified casks for whisky maturation. The casks were used for fermentations and maturation of sherries in Spain before they were shipped usually as empty standing casks to Scotland. According to the distiller's order, both American (Quercus alba) and Spanish (Q.robur) oak were used, as well as fino and oloroso sherries.

According to a rumour the Scotch Whisky Association banned the use of paxarete in the late 1980s or early 1990s, but there is no official evidence of that. The Scotch Whisky Order from 1990 bans the use of additives other than water and caramel E150a, so the blending of whisky with sherry wine including pajarete was indeed banned at that point. PX sherry casks are still quite often used especially for single malt production, but the use of sherry concentrates and high pressures in rejuvenation and seasoning has apparently ceased or at least diminished greatly. Philip Hills wrote in 2000: "wine-treatment of worn-out casks has been widely used to simulate the effects of new sherry wood... a sweet dark sherry such as pedro ximenes [sic] is introduced and the cask is pressurised in order to force the potion into the wood. For many years, a potion called paxarette was used, which combined sweet dark sherry with other flavourings and colourants... the results are not impressive: whisky from a treated cask of this sort smells slightly sulphurous and sweet, but that is all. Of the lovely aromatic flavours of a true sherry-cask maturation, there is no trace.". It is likely that the wine-treatment was dropped because of the poor results rather than an SWA order. Below is a comparison of different cask types and maturation temperatures.

Philp 1989

Oloroso and raya sherries are probably the most common seasoning sherries used nowadays, seasoning times varying from months to couple of years. Cask fermentations are rarely done in the Scotch-bound casks. The sherry bodega casks used for maturation of commercial sherries in solera systems are discarded usually after 80-100 years and sometimes  used for Scotch maturation after recoopering.

REFERENCES AND FURTHER READING:

Conner JM et al. Changes in wood extractives from oak cask staves through maturation of scotch malt whisky. J Sci Food Agric 1993;62;169-174
Crawfowd, A. Bristol wine trade. Historical association 1984
Glasgow Herald 27.5.1969

González Gordon M, Sherry. Cassell Ltd 1972
Halley, N. Sandeman: two hundred years of port and sherry. Granta 1990
Harrison, G. Bristol Cream. Batsford 1955
Hills, P. Appreciating whisky. Collins 2000
Hotelli- ja Ravintolamuseon arkisto, Helsinki.
Jeffs, Sherry. 1970
Lea GH, Piggott JR. Fermented beverage production 2nd ed. Kluwer Acad 2003
Morewood, S. A philosophical and statistical history of inventions and customs of ancient and modern nations in the manufacture and use of inebriating liquors. 

Mosedale, JR. Effects of oak wood on the maturation of alcoholic beverages with particular reference to whisky. Forestry 1995; 68; 3; 203-230
Mosedale JR & Puech JL. Wood maturation of distilled beverages. Trends Food Sci Tech 1998;9;95-101

Piggott JR et al. Effects on scotch whisky composition and flavour of maturation in oak casks with varying histories. Int J Food Sci Tech 1993;28;303-318
Piggott, JR et al(ed). The Science and technology of whiskies. Longman 1989

Read J. Sherry and the sherry bodegas. Sotheby's 1988

Reid KJG et al. Understanding and enhancing cask performance. The Scotch Whisky Research Institute 2008.
Sykes WJ, Ling AR. The principles and practice of brewing. Griffin 1907
Wright HE. A handy book for brewers being a practical guide to the art of brewing and malting, embracing the conclusions of modern research which bear upon the practice of brewing. Lockwood & Son 1897