The principals for the distillation of whisky have changed little over the last 200 years. Just three basic ingredients are needed - water, barley and yeast. Technology now aids production at most distilleries, but traditionally there are five stages to the process - malting, mashing, fermentation, distillation and maturation. Understanding the whisky making process shows how the highly skilled distillers can influence the final flavour of the spirit at every stage.
Step 1 - Malting
Barley contains starch and it is this starch which needs to be converted into soluble sugars to make alcohol. To begin this process, the barley must germinate and this is called 'malting'. Each distiller has their own preference about the type of barley they buy, but they need a type that produce high yields of sugar when fermented. The barley is soaked for 2-3 days and then spread on the floor of a building called a malting house (like the one at Springbank distillery above). It is turned regularly to maintain a constant temperature. When the barley has started to shoot, the germination is stopped by drying it in a kiln. Traditionally peat is used to power the kiln and it is at this point where the type of peat used and length of drying in the thick peat smoke can influence the flavour of the final spirit. The barley is now called 'malt' and this is ground down in a mill, with any husks and other debris being removed. This finely ground malt is now called 'grist'.
Step 2 - Mashing
Hot water is now added to the grist. The water is normally from a pure, reliable, local source. The character of this water can influence the final spirit as it can contain minerals from passing over or though granite, peat or other types of rock. Most distilleries use soft water. This mixture is put into a large vessel called a mash tun and stirred for several hours. During this process, the sugars in the malt dissolve and these are drawn off through a large seive at the bottom of the mash tun. This liquid is now called 'wort'. This process is normally carried out three times with the water temperature being increased each time. Only wort from the first two times is used. The third lot is put back into the next batch of new grist. Any residue, called 'graff', is collected and used in the production of farm feed.
Step 3 - Fermentation
The wort is cooled and passed into large tanks called washbacks. These are traditionally made of oak wood, but now a number of distilleries use stainless steel. Here the yeast is added and the fermentation begins. The yeast turns the sugars that are present in the liquid into alcohol. As with the choice of barley and water, the distiller will carefully select the type of yeast that they use and it can also have an effect on the final flavour of the spirit. The fermentation is stopped after about two days. The liquid at this stage is called 'wash' and is low strength (between 5-10% ABV) and is very much like a beer or ale. You could actually make beer from the liquid at this point, but the difference with whisky is that the liquid is now distilled rather than brewed.
Step 4 - Distillation
In Scotland, the wash is traditionally distilled twice. In Ireland, it is distilled three times although there are exceptions in both countries. Here, we will follow the Scottish double distillation process. The stills are made from copper and consist of a bowl shape at the bottom that rises up to the neck at the top. All are the same in principal, but a different shape will give a different flavour to the final spirit. Taller stills with longer necks will give finer, lighter spirits while shorter, fatter stills will produce a fuller, richer spirit.
Firstly, the wash enters the wash still and is heated (this can be by coal, gas or steam). The liquid vaporises and rises up the still until it reaches the neck, where it condenses. This liquid is called 'low wines'. The low wines are passed to the second still, called the spirit still. Any residue from the wash still is collected and used to manufacture farm feed. In the spirit still, the alcohol produced is split into three. The alcohols from the beginning of the distillation (called 'foreshots') are very high in alcohol level and very pungent. Alcohols from the end (called 'feints') are weak but also pungent. It is only the alcohol from the middle or 'heart' of the distillation that is used and this is skillfully removed by a stillman. The foreshots and feints are then mixed with the next batch of low wines and re-distilled. The heart is the spirit that is then taken to be matured and that will become whisky.
Step 5 - Maturation
The spirit is put into oak casks and stored. The most common types of oak casks are those that have previously been used in the American bourbon and Spanish sherry industries or those that have been used to mature whisky before. The spirit must mature in casks for a minimum of three years before it is legally allowed to be called whisky. During maturation, the flavours of the spirit combine with compounds and natural oils in the wood cask and this gives the whisky it's own characteristic flavour and aroma.
Wood is porous, so over time it will breathe in air from the surrounding environment in which it is stored. This will also give the whisky some unique characteristics. If the distillery storage facilities are next to the sea, on an island or in the middle of the highlands then the air quality, temperature and humidity will be different and influence the end product. During each year of maturation about 2% of the spirit is lost through natural evaporation. This is called the 'angel's share' and explains why older whiskies are less readily available and more expensive to buy. There is simply less whisky in the cask to bottle.
Bruichladdich, a distillery on the island of Islay, have webcams that allow you to see each of these processes as they are happening. Go to http://www.bruichladdich.com/web_cam.htm and watch their whisky being produced live.