Types of whisky
Malt whisky must contain no grain other than malted barley and is traditionally distilled in pot stills. Grain whisky may contain unmalted barley or other malted or unmalted grains such as wheat and maize (corn) and is typically distilled in a continuous column still, known as a Patent or Coffey still, the latter after Aeneas Coffey who refined the column still in 1831. While there are scores of malt whisky distilleries, only seven grain distilleries currently exist, most located in the Scottish Lowlands.
Malt whisky production begins when the barley is malted—by steeping the barley in water, and then allowing it to get to the point of germination. Malting releases enzymes that break down starches in the grain and help convert them into sugars. When the desired state of germination is reached the malted barley is dried using smoke. Many (but not all) distillers add peat to the fire to give an earthy, peaty flavour to the spirit.
Today only a handful of distilleries have their own maltings; these include Balvenie, Kilchoman, Highland Park, Glenfiddich, Glen Ord, Bowmore, Laphroaig, Springbank, Tamdhu, and Edradour. Even those distilleries that malt their own barley produce only a small percentage of the malt required for production. All distilleries order malt from specialised maltsters.
Mashing and fermentation
The dried malt (and in the case of grain whisky, other grains) is ground into a coarse flour called "grist". This is mixed with hot water in a large vessel called a mash tun. The grist is allowed to steep.
This process is referred to as "mashing", and the mixture as "mash". In mashing, enzymes that were developed during the malting process are allowed to convert the barley starch into sugar, producing a sugary liquid known as "wort".
The wort is then transferred to another large vessel called a "wash back" where it is cooled. The yeast is added, and the wort is allowed to ferment. The resulting liquid, now at about 5–7% alcohol by volume, is called "wash" and is very similar to a rudimentary beer.
The next step is to use a still to distill the wash. Distillation is used to increase the alcohol content and to remove undesired impurities such as methanol.
There are two types of stills in use for the distillation: the pot still (for single malts) and the Coffey still (for grain whisky). Most Scotch malt whisky distilleries distill their product twice; exceptions include the Auchentoshan distillery and Springbank's 'Hazelburn' brand, which retain the Lowlands tradition of triple distillation. A third method is unique to the Springbank distillery's 'Springbank' brand, which is distilled "two-and-a-half-times". This is achieved by distilling half the low wine (1st distillation) for a second time, adding the two halves together and then distilling the complete volume a final time.
For malt whisky the wash is transferred into a wash still. The liquid is heated to the boiling point, which is lower than the boiling point of water. The alcohol evaporates and travels to the top of the still, through the "lyne arm" and into a condenser—where it is cooled and reverts to liquid. This liquid has an alcohol content of about 20% and is called "low wine".
The low wine is distilled a second time, in a spirit still, and the distillation is divided into three "cuts". The first liquid or cut of the distillation is called "foreshots" and is generally quite toxic due to the presence of the low boiling point alcohol methanol. These are generally saved for further distillation. It is the "middle cut" that the stillman is looking for, which will be placed in casks for maturation. At this stage it is called "new make". Its alcohol content can be anywhere from 60%–75%. The third cut is called the "feints" and is generally quite weak. These are also saved for further distillation.
Grain whiskies are distilled in a column still, which requires a single distillation to achieve the desired alcohol content. Grain whisky is produced by a continuous fractional distillation process, unlike the simple distillation based batch process used for malt whisky. It is therefore more efficient to operate and the resulting whisky is less expensive.
Once distilled the "new make spirit" is placed into oak casks for the maturation process. Historically, casks previously used for sherry were used (as barrels are expensive, and there was a ready market for used sherry butts). Today, the casks used are typically sherry or bourbon casks. Sometimes other varieties such as port, Cognac, Madeira, calvados, beer, and Bordeaux wine are used. Bourbon production is a nearly inexhaustible generator of used barrels, due to United States regulation requiring the use of new, freshly-charred oak barrels in the maturation.
The ageing process results in evaporation, so each year in the cask causes a loss of volume as well as a reduction in alcohol. The 0.5–2.0% lost each year is known as the angel's share. Many whiskies along the west coast and on the Hebrides are stored in open storehouses on the coast, allowing the salty sea air to pass on its flavour to the spirit. It is a little-known fact, however, that most so-called "coastal" whiskies are matured in large central warehouses in the Scottish interior far from any influence of the sea. The distillate must age for at least three years and one day in Scotland to be called Scotch whisky, although most single malts are offered at a minimum of eight years of age. Some believe that older whiskies are inherently better, but others find that the age for optimum flavour development changes drastically from distillery to distillery, or even from cask to cask. Older whiskies are inherently scarcer, however, so they usually command significantly higher prices.
Colour can give a clue to the type of cask (sherry or bourbon) used to age the whisky, although the addition of legal "spirit caramel" is sometimes used to darken an otherwise lightly coloured whisky. Sherried whisky is usually darker or more amber in colour, while whisky aged in ex-bourbon casks is usually a golden-yellow/honey colour.
The late 1990s saw a trend towards "wood finishes" in which fully matured whisky is moved from one barrel into another one that had previously aged a different type of alcohol (e.g., port, Madeira, rum, wine, etc.) to add the "finish".
A notable example is the "Black Bowmore", released in batches in 1993, 94 and 95 after 29, 30, 31 years in ex-Oloroso sherry casks. The name evokes the density of colour and complexity of flavour naturally imparted into what was originally water-clear spirit in 1964.
With single malts, the now properly aged spirit may be "vatted", or "married", with other single malts (sometimes of different ages) from the same distillery. The whisky is generally diluted to a bottling strength of between 40% and 46%.
Occasionally distillers will release a "Cask Strength" edition, which is not diluted and will usually have an alcohol content of 50–60%.
Many distilleries are releasing "Single Cask" editions, which are the product of a single cask which has not been vatted with whisky from any other casks. These bottles will usually have a label which details the date the whisky was distilled, the date it was bottled, the number of bottles produced, the number of the particular bottle, and the number of the cask which produced the bottles.
Many whiskies are bottled after being chill-filtered. This is a process in which the whisky is chilled to near 0°C (32°F) and passed through a fine filter. The result is to remove some of the oily/fatty compounds produced during distillation or extracted in the maturation period. It prevents the whisky when in the bottle at an alcohol level below 46%abv or when served from becoming hazy when chilled, or when water or ice is added.
It is believed by many whisky enthusiasts that chill-filtration removes some of the flavour and body from the whisky, which is why some consider chill-filtered whiskies to be inferior.
Generally bottled whisky over 46%abv will indicate that it is non-chill filtered or unchill-filtered, as the spirit will generally remain unclouded at this alcohol level