The Raw Materials

Scotch Whisky is made from only three ingredients, BARLEY, WATER and YEAST. All of these ingredients are used in their purest, unadulterated, natural form. However, two of the most important flavouring influences are OAK CASKS that are used for maturation of the new spirit, and PEAT which is (traditionally) used to fire the kilns that dry the barley, where it also imparts distinctive flavours. We'll consider each of these materials below.

Barley contributes more in way of flavour than any of the other cereals and the best flavoured grain spirits are those which use the highest percentage of barley in their mash. Barley starting to germinate, now known as "green malt". The grain stores its energy as starch which it converts to sugar as it begins to grow.   The green malt must be turned regularly to keep it cool and prevent the rootlets from becoming matted. Very few distilleries today carry out this practice with most malting carried out in large automated factories.

Barley is a cereal crop of the genus Horndeum, a grass-type crop which yields starchy seeds rich in carbohydrates and suitable for food. It is arguably, the easiest of all cereals to grow, hence its popularity from the earliest times and thankfully for the Scots, varieties which thrive in the cold and wet have been cultivated for thousands of years. Subsequent developments in farming have led to new varieties and strains of barley such as Puffin, Pipkin, Camargue, Prisma and Golden Promise, which give higher yields in the field, tougher and shorter straw for better harvesting, improved malting capabilities and subsequently higher yields in the distillery. More importantly, barley is the reason why malt whisky tends to taste 'better' than other kinds of whisky: quite simply, it contributes more flavour than other cereals. If you've ever tasted a grain whisky (made mainly from maize or some other grain like wheat), you'll have noticed they're much lighter flavours.  As to whether the type of barley used effects whisky (as it does in beer production), there is little agreement within the whisky industry at present though Macallan, who almost exclusively use Golden Promise barley to make their single malts, have long believed it contributes to a superior product.

It's been said that while brewing beer requires around ten litres of water for every litre of ale, to get the same volume of whisky requires closer to 100 litres of water. Not surprisingly, distilleries usually have their own water supplies, often a loch or spring to which they own exclusive rights. The available water often dictates the siting of a distillery at the outset, and it's common for all distilleries to claim that their water is 'the best in the whole of Scotland'. It's certainly true that Highland water is very pure as there is no heavy industry or intensive farming to contaminate so it's usually used at the distillery untreated save for basic filtering to remove foreign matter. Water is involved in every stage of the production process: To steep the barley prior to malting and for mashing the grist in the mash tun; to cool the condensers (or worm tubs) and finally, if desired, to reduce the finished product to a standard alcohol strength prior to bottling.

is a fungus or mould, a single-cell organism containing enzymes, biochemical catalysts which cause certain chemical reactions to take place. The obvious reaction which  interests brewers and distillers is that which converts sugars into alcohol. Yeast is usually inactive in its stored state. In distilling, it is activated by the temperature of the wort in the washback. The yeast multiplies at a phenomenal rate during the fermentation, feeding on the sugars in the wort, and it is eventually killed by the very alcohol it produces. Distillers commonly use two types of yeast, Brewer's Yeast which is produced as a by-product in the brewing industry with a comparatively short shelf-life and Cultured Yeast which is grown on suitable nutrients under laboratory conditions with a far higher viability. The second important requirement of yeast is its contribution to flavour which, as in wine production, tends to be strain dependent.

If you love peaty whiskies but don't quite understand why they taste like they do, it's because of peat, or more precisely, peat smoke, which when burnt releases chemicals called phenols. These phenols are absorbed by the malted barley during the drying process in a kiln. The level of phenols is measured in ''PPM' (parts per million) and controlled by the length of time that the barley is exposed to the smoke, the amount of smoke produced and the type of peat used.

Even if 'bogs' are not your thing, peat is actually far more fascinating than first impressions might suggest. It is a relic of the Carboniferous period some 300 million years ago when much of what is now Britain was swampland. As trees, roots, ferns, grasses, animals and even people died or fell into the swamps they were subsumed into the stagnant water and partially decomposed, but did not rot away entirely. Instead an organic fuel formed by their decomposition. Peat is black because of its rich carbon content (the CO2 is not released into the atmosphere as normally takes place in decomposition around oxygen). Yet compared to wood, peat is relatively inefficient to burn. Without a proper furnace, it tends to smoke rather than create much heat.

For a long time a lack of alternative fuel forced 'Highlanders' to burn peat. Coal was simply too expensive for most and there were few trees. The situation began to change around the turn of the 1960's, with the help of technological progress in large industrial scale maltings. It then became possible to produce vast quantities of malted barley without peat. Speyside and Lowland distilleries were amongst the first to change to coke (a high carbon form of coal) as a combustible, as new railway networks to transport the fuel encouraged the transition. Remoter regions like Islay persisted with peat.

Today, there's no question that peat-smoke derived flavours in whiskies are increasingly desirable. Consequently, peat is now used not only on Islay by the likes of Ardbeg, but also on Orkney, in the Highlands, Campbeltown, as well as in Speyside. Peat is usually extracted close to the distillers or maltsters. Distilleries prefer the top part of the bog, because the upper crust of peat found there tends to be 'richer', more rooty and generate more smoke and impart more flavour.

At some stage of his or her drinking career, every hairy chested peat freak has probably wondered "Why don't peaty whiskies all have the same kind of 'peatiness'." Instead, we find that peat comes in a remarkable array of sensory guises, and also contributes an almost oily mouth feel, as well as added depth, richness and sweetness. Its flavours are expressed differently in whiskies from different distilleries and range from notes reminiscent of lanolin, wet wool, iodine, seaweed, bacon, tobacco smoke, engine oil, tar, manure and wet earth.

As much of Scotland is (in parts) covered by a meter-thick layer of peat, it's been supposed that different types of organic matter in the different regions, have created different types of peat which impart, in turn, different flavours to the finished whisky. For example, historically there have been few trees on the Orkney islands so there are no tree roots in the peat, making it lighter and quicker to burn. Whiskies from this area, like Highland Park, tend to have a more lightly smoked flavour than Islay malts.
Is this an argument for 'peat' and 'terroir'?

Three examples of smokey style whiskies, made using varying degrees of peat.
Laphroaig often posseses a slight medicinal character. Ardbeg in the centre, also from the island of Islay is renowned for its full throttle peat experience that tends to polarise whisky lovers, while Ledaig is an unusual expression from the Isle of Mull, made at the Tobermory Distillery.

Patrick Brossard of recently reported on a study that approaches this question. In 2009, B.M. Harrison and F.G. Priest published an article on the composition of peat in the production of Scotch Whisky and the influence of its geographical source, extraction depth and burning temperature: "Peat samples from four locations (Islay, Orkney, St. Fergus (Aberdenshire), and Tomintoul (Speyside) were analyzed using Curie point pyrolysis in combination with gas chromatography-mass spectrometry".
[As in the simpler process of distillation where small molecules fly out first, followed by the big ones (so alcohol is separated from water), with gas chromatography a sample is heated to evaporation in order to release volatile compounds. Since all the molecules of a given structure will behave more or less identically, they exit the machine collectively and at the same time. As each 'puff' of molecules is released, a computer generated graph peaks corresponding to the most abundant chemical compounds. The higher the peak, the greater the number of molecules of acertain type are present].

"In total, out of the 106 products identified, 92 compounds were having a significant effect on the separation of the four geographical locations. The compounds were broadly split into the following classes: phenolic compounds, carbohydrate derivatives (“sugars”), aromatic compounds, and nitrogen-containing compounds".

"The ratio of phenol derivatives (carbohydrate derivatives to guaiacols, syringols, and phenols) was the major discriminator between the samples of the different geographical regions, explaining more than 60% of the variance. St. Fergus and Islay samples were characterized by high percentages of guaiacols (aromas described as aromatic, phenolic, burnt, woody, bacon, savoury, smoky, and medicinal), syringols (aromas described as aromatic, phenolic, spicy, smoky, baconlike, sweet, medicinal, creamy, meaty, and vanilla), and phenols (aromas described as aromatic, phenolic, burnt, woody, bacon, savoury, smoky, and medicinal) in the pyrolysate [i.e. burnt peat]. Relatively high proportions of carbohydrate derivatives in the [burnt peat] characterized Tomintoul and Orkney samples."

"In the distillate (new make), the origin of the peat could be clearly identified by analytical methods. By sensory analysis (by “human nose”), the spirits using Tomintoul (Speyside) peat were more medicinal than the spirit using Hobbister (Orkney) peat. The level of peat aroma was low in the St-Fergus spirit (Aberdeenshire) despite a high abundance of aromatic peaty aromas, but the spirit was sweet, spicy and medicinal."

The upshot of the study indicates that the source of peat will have an impact on the flavour of the whisky. It's a conclusion which may reignite the debate over Scotch whisky 'terroir' beyond the simplistic Highlands / Islands / Lowlands trichotomy.

As a footnote, to this subject, it's also been suggested that peat flavours can be derived via the use of water which flows naturally over and/or through uncut peat beds. However, research indicates peat water contains only a few ppm (parts by million) of peat, which while enough to colour the water brown, contributes little or nothing to whisky flavour.

The chemical processes behind maturation of spirits in oak barrels are at least as complex as they are for wine, but even more fundamental to the end result. Phillip Hills comments "[Barrel] maturation is easily the most important part of the [Scotch] whisky production process as regards flavour. A malt whisky acquires more than half of its flavour during maturation; some would say as much as 80 per cent of the final flavour of the spirit comes from the cask."

Historically, a wide variety of casks were purchased for Scotch Whisky production including former Sauternes, Sherry, Madeira, Bordeaux, Port, Moscatel and Burgundy barrels. Nowadays, barrels which have previously contained Sherry or Bourbon are typically used, though Bourbon barrels are now more common: Firstly because they're cheaper, and secondly because x-Bourbon barrels have all of the harsh tannin removed, resulting in a smoother spirit. Glenmorangie's Dr. Bill Lumsden makes an interesting distinction: The first time such barrels are filled with Scotch whisky, they tend to impart toffee, caramel and creme brulee characteristics, whereas second fill casks are where floral and citrus flavours emerge. He also insists that by the time the second fill is matured, the barrel is no longer suitable for whisky production. By changing the ratio of first to second fill wood, a range of flavour profiles can be achieved. There are other variables: Low char new oak contributes 'sizzling' warmth & European oloroso sherry oak casks contribute buttery/vanilla notes. For some time now, Glenmorangie have been pioneering new research into the why and how of spirit maturation with huge dollars devoted to research and development to find the right wood source for casks. Other distilleries are now waking up to this and are becoming more conscientious about oak selection.

Three examples of Highland Single Malt Whisky, each bottled at a different age. 
Many consider 12 - 18 years in barrel to be the optimum period before bottling Scotch, however the mysteries of oak maturation can yield stunning results well passed 20 years of age. They are probably more the exception than the rule.

The optimum period for the barrel maturation of spirits is to some extent a matter of taste and type, however, for Scotch whiskies, the consensus seems to be around 12 to 18 years. At greater ages many whiskies (and other spirits) fall out of balance and become unpleasantly woody, yet others can go on to reach fifty years or more and remain undiminished. Because some whiskies mature faster than others depending upon a host of variables, it is only sensible that distillers and blenders concern themselves more with balance and maturity than age for the sake of age.

The Pot Still process by which Malt Whisky is made may be divided into four main stages: Malting, Mashing, Fermentation and Distillation.

Harvested barley is first screened to remove any foreign matter and then soaked for two or three days in tanks of water known as steeps. It's then spread out on a concrete floor known as the malting floor and allowed to germinate. Germination may take from 8 to 12 days depending on the season of the year, the quality of the barley used and other factors. During germination, barley secretes the enzyme diastase which makes the starch in the barley soluble, thus preparing it for conversion into sugar. Throughout this period the barley must be turned at regular intervals to control the temperature and rate of germination.

At the appropriate moment germination is stopped, otherwise the seed would continue to grow until all the sugars where consumed. This is achieved by drying the malted barley or green malt in a malt kiln. More usually nowadays malting is carried out in Saladin boxes or in drum maltings, in both of which the process is controlled mechanically. Instead of germinating on the distillery floor, the grain is contained in large rectangular boxes (Saladin) or in large cylindrical drums. Temperature is controlled by blowing air at selected temperatures upwards through the germinating grain, which is turned mechanically. A recent development caused by the rapid expansion of the Scotch Whisky industry is for distilleries to obtain their malt from centralised maltings which supply a number of distilleries, thereby enabling the malting process to be carried out more economically. More traditional distilleries will still use a clean coke fire to dry the barley with the peat burnt on top of the coke to give whatever degree of 'smokiness' is desired. When peat is burnt, chemical compounds in it adhere to the malted barley and remain throughout the life of the whisky, diminished only by extended periods of oak maturation.

Dried malt from the kiln is crunchy and pleasantly sweet. In this state, it's easily ground in a mill with the resulting grist, as it's now called, then mixed with hot water in a large circular vessel called a mash tun, usually made out of cast iron or stainless steel. The soluble starch is thus converted into a sugary liquid known as wort. This is drawn off from the mash tun and the solids remaining are removed for use as cattle food. Importantly, the degree of filtration of the mash can effect the flavour of the whisky, and the presence of some solid material in the wort has been found to be beneficial.

After cooling, the wort is passed into large vessels known as 'washbacks', holding anything from 9,000 to 45,000 litres of liquid where it is fermented by the addition of yeast. The living yeast attacks the sugar in the wort and converts it into crude alcohol. Fermentation takes about 48 hours and produces a liquid known as wash, containing alcohol of low strength (essentially beer), some unfermentable matter and certain by-products of fermentation such as esters, fatty acids and aldehydes amongst many other compounds believed to be significant to a whisky's final flavour. Some distillers consider wooden washbacks to be  superior to stainless steel (and vice versa) though both seem to result in good whisky.

Malt Whisky is distilled twice in large copper Pot Stills in which the liquid wash is heated to a point at which the alcohol becomes vapour. This rises up the still and is passed into the cooling plant where it is condensed into liquid state. The cooling plant frequently takes the form of a coiled copper tube or worm that is kept in continuously running cold water.

The first distillation takes place in large wash stills, and separates the 99% of the alcohol from the fermented liquid and eliminates the residue of the yeast and unfermentable matter. Now much reduced in volume, the resulting liquid, known as low wines (approx 21% Alc./Vol.), is ready to be passed into another still to be distilled a second time. The first runnings from this second distillation (known as 'foreshots' or 'heads') are not considered potable, and by experience a distiller learns to re-direct these back into the low wines receiver to be distilled again. It is the middle part of the distillation (often referred to as the heart) when the spirit reaches an acceptable standard that it's collected in the spirit receiver. Towards the end of the batch, again, the spirit begins to fall off in strength and quality. Known as the 'tail' or 'aftershots' It is no longer collected as spirit but drawn off and kept, together with the first running, for redistillation with the next low wines. Consequently, pot still distillation is a batch process. (Some distilleries re-heat the middle cut to further exclude all but the purest ethanol from the new middle cut - this is a triple distillation). The 'heart' of the distillation is destined to become whisky, but before extended maturation in oak, this 'new make spirit' is more like a high proof vodka or tequila - crystal clear, usually with subtle fruity, flowery aromas and a sweet, spicy flavour profile. Smelling or tasting fresh whisky distillate serves to illustrate the profound impact that wood maturation has on whisky flavour.

Making Grain Whisky

The chemical processes which take place during the manufacture of grain spirit are broadly similar to those which occur when malt whisky is made. Both the raw materials and the equipment are different, however. The mash from which grain whisky is made uses unmalted cereals - usually wheat or maize, it doesn't matter which, so distilleries can buy at the best price - together with a small amount of 'green'malt (barley which has germinated but not been kilned). Usually about 16% of malt is added: it has to be there to convert the starches in the other cereals into sugar, so it can be turned into alcohol by the yeast.

Mashing and Fermenting

The cereals are finely milled then cooked at high temperatures in a pressure cooker. The pressure is provided by the direct injection of steam, and the purpose of the cooking is to soften the husks of the grain and dissolve the starch into solution.The slurry thus created is cooled and transferred to the mash tun, where a measured amount of green malted barley is waiting, and the whole lot is mashed (i.e., converted into a sugar solution), as for malt whisky.

Oils in the maize
The wort, and any solids it contains, is drained off after an hour or so, cooled and pumped to a fermentation vessel, where yeast cream is added. Fermentation continues for forty-eight hours, during which time the sugar is converted into alcohol (at between 6% and 7%) and carbon dioxide.The wash for grain whisky does not bubble quite so vigorously, because of the oils in the maize. It is also lower in alcohol.