82 GEOLOGY OF WHISKY GEOLOGY OF WHISKY S J Cribb, Carraig Associates, Inverness, UK ß 2005, Elsevier Ltd All Rights Reserved Introduction The distillation of liquors produced by the fermentation of cereals is a process that goes back into the mists of history There is historical evidence from Scotland dating the distillation of malted barley from the middle of the sixteenth century The distillate was known originally by its Gaelic name uisge beathe (‘water of life’), which has become the present-day word ‘whisky’ (spelt variously in many countries with or without an ‘e’) The distilling process was legalized in Scotland in the 1830s, and since then the manufacture of this special liquid, whisky, has been developed to a fine degree, as is evident in the array of unique products available today The manufacture of whisky occurs in many countries, but the pinnacle of success with this product is found in Scotch whisky, a specific product of Scotland To qualify as Scotch whisky, the spirit must be derived from malted and/or unmalted cereals and be matured in oak barrels in Scotland for at least years Whiskies fall into three categories: grains, malts, and blends Grain whisky is manufactured generally by a continuous industrial process from malted and unmalted cereals Malt whiskies are made totally from malted barley Blended whiskies comprise a base of between 40 and 60% grain whisky overlain by up to 30 malts Malt whisky represents probably the pinnacle in the development of the whisky-making process and of the 100 or so distilleries in Scotland, around 75 are producing at any one time Each of these distilleries produces a unique spirit characterized partly by the unique source of water for its production, and it is in the chemistry of this that the varying geology of the water sources comes into play Whisky Production The whisky-making process essentially comprises a brewing phase, followed by the distillation of the resulting liquor In fact, the result of the first stage is the production of the equivalent of a strong beer, though unflavoured by hops or other additives The first part of this process is the malting of barley, whereby the grain is encouraged to germinate for several days to initiate the enzyme processes that break down starch to sugars, before the process is stopped by heating Traditionally, where the malting takes place at a distillery site, a certain amount of peat smoke is allowed to permeate the malt during the heating process The level of permeation is reflected in the smokiness of the final product Nowadays there are larger scale centralized maltings serving several distilleries, but the process of peating is essentially the same The second stage is the mixing of the malted barley with fresh potable water to extract the sugars and produce a liquor ready for fermentation Fermentation takes place using a combination of beer and wine yeasts to raise the alcohol content to around 8% The resulting liquid is then heated in the distinctive onion-shaped copper stills, normally in a twostage process that raises the alcohol content, first to 25% and second to the final spirit alcohol content of between 55 and 65% alcohol The raw spirit is stored in oak barrels of various types: new wood, European oak barrels generally from the sherry industry in Spain, and American oak bourbon barrels Thus the four crucial factors that combine to produce the wide variety of malt whiskies are the degree of peating of the malt, the shape and type of still, the types of barrels used for maturation, and the chemistry of the process waters It is with the latter step that the geological influence on whisky type is exerted Water chemistry affects three areas of the production process: the extraction of sugars from the malt, the nature and type of fermentation, and the chemistry of the distillation process (which is largely unstudied) There is an oft-quoted maxim that the best type of water for the production of malt whisky is soft water through peat over granite Even a cursory comparison of the siting of malt whisky distilleries with the geological map of Scotland will show that only in comparatively rare instances is it likely that such water will be available In fact, only 20 distilleries, most of which are centred in the Speyside area of north-east Scotland, have such water The remaining rock types from which water is sourced cover the whole spectrum from sandstones and schists to quartzites and shales Clearly the chemistry of the waters derived from such a range of sources will show significant variations up to and including significantly heavily mineralized (hard) waters Distilleries Distilleries come in all shapes and sizes and they are situated on the coast, inland, on hills, in valleys, by mighty rivers, near small streams, and on islands