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.
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 produce the necessary enzymes required to convert starch into fermentable sugars.
Traditionally each distillery had its own malting floor where the germinating seeds were regularly turned. Most of the distilleries use commercial "maltsters" who prepare each distillery's malt to exact specifications, but the "pagoda roof" (many now false) which ventilated the malting floor can be seen at nearly every distillery.
The germination is halted (by heating) after 3-5 days, before the starch begins to be converted into the 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 from Islay have phenol levels between 25 and 50 parts per million (ppm). The three smokiest/peatiest malts, in order of phenol concentration, are Ardbeg, Laphroaig (la-froyg) and Lagavulin (lagga-voolin), all from Islay. More subtle malts can have phenol levels of around 2–3 ppm.
The extraction is done in a large kettle (usually made of stainless steel) called a mash tun. At first, the hot water activates the enzymes by providing an optimal temperature for activity in the grist. The enzymes act on the starch to convert it into sugar, and producing a sugary liquid called wort.
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.
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 in the case of Lowlander, Auchentoshan, 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. There are urban legends (mostly untrue) of master distillers having dents placed in brand new stills so that they matched those in the old still. Another urban legend states that one distiller refuses to allow the cobwebs to be cleaned off his stills for fear of altering the whisky.
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 in Scotland; 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 decreases the alcohol content of the whisky. The lost volume from evaporation is known as the angel's share.
The selection of casks has a profound effect on the character of the final whisky. Single malt Scotch is too delicate to be aged in new oak casks, as new oak would overpower the whisky with tannin and vanillin, making it overly astringent. Thus used casks are needed. The most 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. An important minority of whisky maturation occurs in sherry casks. 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. Sherry casks are more expensive than bourbon casks, and account for only seven percent of all casks imported for whisky maturation. In addition to imparting the flavours of their former contents, sherry casks lend maturing spirit a heavier body and a deep amber colour. For this reason, single malt Scotches that have been matured in sherry casks are especially prized by blenders, as they give a blend a roundness and richness. 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 red wine, rum and cognac casks are being performed.
The age statement on a bottle of single malt Scotch 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.
It should also be noted that for whisky, unlike wine, the maturation process does not continue in the bottle.
Independent bottlers, such as Gordon & MacPhail, Murray McDavid, Signatory, Hart Brothers, and Cadenhead, buy casks of single malts and either bottle them immediately or store them for future use. Many of the independents began as stores and merchants who bought the whisky in bulk and bottled it for individual sales. Many distilleries do not bottle their whisky as a single malt, so independent bottlings are the only way the single malt gets to market. The bottling process is generally the same, but independents generally do not have access to the distillery's water source, so another source is used to dilute the whisky. Additionally, independents are generally less concerned with maintaining a particular style, so more single year and single cask bottlings are produced.
In the following centuries, the various governments of Scotland began taxing the production of whisky, 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 a continuous still 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 Scotch 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. As of 2004, over 90% of the single malt Scotch produced is used to make blended Scotch.
Most distilleries in Scotland are not owned by Scots. The Japanese beverage company Suntory owns Morrison-Bowmore, while other international companies, such as LVMH & Pernod-Ricard (France), and Diageo (England), own the majority of distilleries. The largest distiller to remain under Scottish ownership is William Grant & Sons, owned by the Grant family, with headquarters in Motherwell, Scotland. Other distilleries owned by Scottish companies/families are Glenfarclas, Bruichladdich, and Bunnahabhain.
Flavour, aroma, and finish differ widely from one single malt to the next. Single Malt Scotch whiskies are categorised into the following whisky-producing regions.