Production
All single malt goes through a similar batch production process, as outlined below. At bottling time various batches are mixed together or vatted to achieve consistent flavours from one bottling run to the next. Some variation does occur.
Water
Water is first added to the barley to promote germination, it is mixed with ground barley grist to create a mash and it is used to dilute most whisky before maturation and once again before bottling.
Most distilleries use different water sources in the various steps.
Most new-make malt whisky is diluted to about 63.5% before it is placed in casks to mature. These days, many distilleries are using distilled water for diluting whisky before it is casked as well as for diluting the whisky to bottling strength (40-46% Alcohol by Volume (ABV)) after maturation. Others, like Jura or Bruichladdich use water from local burns or springs to dilute new-make before it is casked. Much new-make whisky is shipped in tanker trucks to central warehouses where local tap water is used to dilute it before casking, and again at bottling time.
Since huge amounts of water are used during the process of whisky production, water supplies are a key factor for the location of any distillery.
Malting
Malted Barley
Barley, yeast and water are the only ingredients required in the production of single malt whisky.
The barley used to make the whisky is "malted" by soaking the grain in water for 2-3 days and then allowing it to germinate to convert starch (which is insoluble in water and not available for fermentation by yeast) to fermentable sugars.
Traditionally in Scotland each distillery had its own malting floor where the germinating seeds were regularly turned. The "pagoda roof" (many now false) which ventilated the malt kiln can still be seen at many distilleries both in Scotland and in other countries. However, most of the distilleries now use commercial "maltsters" to prepare their malt.
The distinctive "pagoda" chimney of a kiln at a distillery in Scotland.
The germination is halted (by heating) after 3-5 days, when the optimum amount of starch has been converted to fermentable sugars. The method for drying the germinated barley is by heating it with hot air produced by an oil, coal or even electric heat source.
In most cases, some level of peat smoke is introduced to the kiln to add phenols, a smoky aroma and flavour to the whisky. Some of the more intensely smoky malts have phenol levels between 25 and 50 parts per million (ppm). The three Scottish malts with a reputation for being the most peaty are Ardbeg, Laphroaig (la-froyg) and Lagavulin (lagga-voolin), all from Islay. More subtle malts can have phenol levels of around 2–3 ppm.
Mashing
The malt is milled into a coarse flour (grist), and added to hot water to extract the sugars.
The extraction is done in a large kettle (usually made of stainless steel) called a mash tun. At first, the hot water dissolves the sugars (maltose) and enzymes (diastase) in the grist. Then the enzymes act on the starch left over from the malting stage, continuing the conversion to sugar, and producing a sugary liquid called wort. Typically, each batch of grist is mashed three times or so to extract all the fermentable sugars.
Fermentation
Yeast is used to ferment malted barley in washbacks.
Yeast is added to the wort in a large vessel (often tens of thousands of litres) called a washback. Washbacks are commonly made of Oregon Pine or stainless steel. The yeast feeds on the sugars and as a by-product produces both carbon dioxide and alcohol. This process is called fermentation and can take up to three days to complete. When complete, the liquid has an alcohol content of 5 to 7% by volume, and is now known as wash. Up until this point the process has been quite similar to the production of beer.
Distillation
The wash, 5%–7% alcohol, is distilled in copper pot stills, boosting the alcohol content to 60%–80%.
The wash is then pumped into a copper pot still, known as the wash still, to be distilled. The wash is heated, boiling off the alcohol, which has a lower boiling point than water; the vapour is collected in a condenser which has been submerged in cool water. The lower temperatures cause the vapour to condense back into a liquid form.
This spirit, known as low wine has an alcohol content of about 20 to 40%. The low wines are then pumped into a second pot still, known as the spirit still, and distilled a second, (and sometimes a third) time. The final spirit called "new make spirit" generally has an alcohol content of 60 to 70%.
Much of the body, or mouth feel, of the final whisky is believed to come from the size and shape of the stills used in its production. When a still wears out and has to be replaced, or when a distillery decides to expand the number of stills it operates, precise measurements of the existing stills are taken to ensure the new stills are reproduced exactly like the old.
Maturation
The "new-make spirit", or unaged whisky, is then placed in oak casks to mature. By law, all Scotch whisky must be aged for a minimum of three years in oak casks; though many single malts are matured for much longer. The whisky continues to develop and change as it spends time in the wood, and maturation periods of twenty years or more are not uncommon. Each year spent in the wood results in the evaporation of between 1 and 2% of each casks' contents, depending on the ambient conditions at which the casks are stored. Because alcohol is more volatile, the alcohol content of the remaining whisky also drops over time. This is known as the angel's share.
The selection of casks has a profound effect on the character of the final whisky. A common source of casks is American whiskey producers, as U.S. laws require that bourbon and Tennessee whiskey be aged in new oak casks. Bourbon casks impart a characteristic vanilla flavour to the whisky. Sherry casks are also commonly used. This practice arose because sherry used to be shipped to Britain from Spain in the cask rather than having been bottled, and the casks were expensive to return empty and were unwanted by the sherry cellars. In addition to imparting the flavours of their former contents, sherry casks lend maturing spirit a heavier body and a deep amber and sometimes reddish colour. Stainless steel shipping containers, however, have reduced the supply of wooden sherry casks, to the extent that the Macallan Distillery builds casks and leases them to the sherry cellars in Spain for a time, then has them shipped back to Scotland. Other casks used include those that formerly held port wine and madeira, while experiments with used rum and cognac casks are being performed.
Bottling
To be called a single malt whisky, a bottle may only contain whisky distilled from malted barley produced at a single distillery. If the bottle is the product of single malt whiskies produced at more than one distillery, the whisky is called a vatted malt, blended malt, or pure malt. If the single malt is mixed with grain whisky, the result is a blended whisky. Single malts can be bottled by the distillery that produced them or by an Independent Bottler.
The age statement on a bottle of single malt whisky is the age of the youngest malt in the mix, as commonly the whiskies of several years are mixed together in a vat to create a more consistent house style.
On occasion the product of a single cask of whisky is bottled and released as a "Single Cask."
While "cask-strength", or undiluted, whisky (often having an alcohol content as high as 60%) has recently become popular, the vast majority of whisky is diluted to its "bottling strength" - between 40% and 46% ABV - and bottled for sale.
Whisky can also be "chill filtered". Chill filtration is a process whereby naturally-occurring fatty amino acids in the whisky are grouped together by chilling the whisky, and then filtered out. Most whiskies are bottled this way, unless specified as "unchillfiltred". Unchillfiltered whisky will turn cloudy when stored at cool temperatures or when cool water is added to them, and this is perfectly normal. Unchillfiltered, cask-strength whisky is generally regarded as whisky in its purest form.
It should also be noted that for whisky, unlike wine, the maturation process does not continue in the bottle.
Storage
Whisky should be stored out of direct heat or sunlight, so as not to undergo evaporation, and should be served at room temperature. Corked bottles should also be stored upright, avoiding contact between the cork and the spirit inside. The more contact with the cork whisky has, the quicker the cork will disintegrate and/or affect the whisky's taste.
History
Distillation of whisky has been performed in Scotland and Ireland for centuries. The first written record of whisky comes from 1405 in Ireland, while the production of whisky from malted barley is first mentioned in Scotland in an entry on the 1494 Exchequer Rolls, which reads "Eight bolls of malt to Friar John Cor, by order of the King, wherewith to make aqua vitae." Single malt whisky is associated with the Scottish tradition, although there are Irish single malts.
From the 15th century onwards, whisky was heavily taxed in Scotland, to the point that most of the spirit was produced illegally. However, in 1823, Parliament passed an act making commercial distillation much more profitable, while imposing punishments on landowners when unlicensed distilleries were found on their properties. George Smith was the first person to take out a licence for a distillery under the new law, founding the Glenlivet Distillery in 1824.
In the 1830s, Aeneas Coffey refined a design originally created by Robert Stein for continuous stills which produced whisky much more efficiently than the traditional pot stills, but with much less flavour. Quickly, merchants began blending the malt whisky with the grain whisky distilled in the continuous stills, making the first blended Scotch whisky. The blended whisky proved quite successful, less expensive to produce than malt with more flavour and character than grain. The combination allowed the single malt producers to expand their operations as the blended whisky was more popular on the international market.
