Malt Whisky is made from three ingredients; barley, water and yeast. The following section describes the basic traditional process of making whisky.
The malting process begins as the barley is soaked in water for two-three days in steep tanks. The soaking increases the moisture content of the grains which in turn triggers the germination process. The barley is then moved to a malting facility (e.g. a malting floor or a drum malting) where the germination continues. The purpose of the malting is to convert the starch in the grains into fermentable sugars which will feed the yeast during the fermentation stage. Heat is produced during the germination so it is important to turn the barley continuously to keep the temperature even. If the temperature rises above 22°C the grains will die and the process of converting the starch into sugar will be halted. In a traditional malting floor the barley is turned by hand with wooden shovels called ‘shiels’.
After the germination is completed it is necessary to prevent the grain from developing further, thereby using up its food supply (the fermentable sugars). This is accomplished in a kiln where the malt is dried to remove enough moisture from each grain so that further growth is halted.
A kiln is a two-storey building where the upper floor is perforated to allow hot air to pass through from below. The lower floor contains a furnace where bricks of peat are burned to generate heat and smoke. The heat and smoke rise through the perforations and dry the green malt. It is during this stage that the malt gains its characteristic ‘peat-reek’.
The kiln with its pagoda roof is the most apparent characteristic of a traditional whisky distillery. The roofs are designed to draw the smoke upwards quickly enough so that the malt is not damaged by the heat (the temperature of the malt must be kept under 70°C).
Today the majority of distilleries buy all or most of their malt from centralised commercial maltings such as Port Ellen and Montrose. For example, Glenfiddich buy all their malt whereas Laphroaig malt 30 percent of their barley themselves. Balvenie is an example of a distillery which still do all their malting themselves.
The malt is ground to grist in a mill and is then fed into mash tuns together with water that holds a temperature of about 60°C. The water is changed three or four times during the eight-hour mashing period and the temperature is increased each time. The mashing creates a sugar solution that is called the wort which is then separated from the spent grains. The mass of used grains is called the ‘draff’ and is not used further in the production process but is commonly used for cattle feed.
The finished wort is quite warm and must be cooled before it can be mixed with the yeast. This is done in the ‘washbacks’. These containers are traditionally made from larch or pinewood but today stainless steel washbacks are also common. Nothing definite can be said as to what effect the use of either material has for the finished product. The size of a washback varies from 6 000 to 45 000 litres. Each washback is never filled to the top since the wort froths significantly during the fermentation, a reaction caused by the release of carbon dioxide. After two to three days the yeast is finally killed by the alcohol it has produced and the fermentation process is finished. The resulting liquid has an alcohol content of 5-8 percent and is called the ‘wash’.
The copper pot stills in which the wash is distilled have become the ultimate symbol of whisky distilleries. The stills are made from copper since it is a material that is easy to work with, it does not rust and it is an efficient heat conductor. The copper is worn down slightly during each distillation however and the thickness must be controlled regularly. The minute copper particles that are released from the still during each run add up over time and a still seldom lasts for more than 25 years. The shape of the stills is very important to the characteristics of the final spirit since it determines how much of the various substances that are allowed to pass through during distillation. Therefore great care is taken to make an exact copy any time a replacement is made.
In general malt whisky is distilled twice although some distilleries practice triple distillation, for example Irish distilleries and a few Scottish distilleries. The stills used for the first distillation is called ‘wash stills’. The resulting ‘low wines’ spirit has an alcohol content of 20-26 percent. The low wines spirit is distilled a second time in ‘spirit stills’.
The ‘stillman’ has the critical task to collect only the desired spirits from the second distillation (the ‘spirit run’). A mistake will likely not be discovered until after the whisky has been stored for several years. At his assistance is the ‘spirit safe’ which was developed in the 1820s to allow the government to control the amount of whisky produced at each distillery. The spirit safe is fitted with hydrometers and thermometers which the stillman uses to determine when the alcohol that exits the still is the correct one for making whisky. Before the desired spirit starts to come through however, the stillman has to avoid the first light alcohols that are called the ‘foreshots’. These are allowed to flow into a separate tank and will later be re-distilled together with the next batch of low wines.
The desired spirit is called ‘the middle cut’ or ‘the heart of the run’ and starts to come through as the alcohol content reaches about 75 percent. The heart of the run is the only part of the distillate that will become whisky. The stillman now diverts the spirit into a separate container. This is called ‘cutting on spirit’. How long the heart of the run continues to flow varies from distillery to distillery but on average the stillman cuts off spirit when the alcohol content of the distillate is down to a little more than 60 percent. The following, more heavy, alcohols are called the ‘feints’ ore the ‘tail’ and are diverted to the same container as the foreshots.
When the spirit is cut on and off varies between distilleries, for example Glengoyne and Aberlour cuts on spirit early at 73 and 71 percent respectively. Some of the heavier more medicinal whiskies such as Laphroaig, Ardbeg and Caol Ila cut off spirit as late as at about 60 percent. Together with the shape of the stills, these differences are among the most important reason behind the different characteristics of these whiskies.
Filling and maturation
After the distillation the spirit is cut to the strength it will have when it is filled into the casks. Most distilleries cut their spirit to 63.5 percent as it is commonly believed that whisky matures best at this specific alcohol content.
All casks used to store whisky are made from oak. Most distilleries use oak casks that have contained sherry or bourbon (Macallan is the only distillery to exclusively use sherry casks). Whisky receives its natural amber colour from interacting with the wood, although it has become increasingly common to artificially add colour by using the E150 additive.
The spirit is not legally considered to be whisky until it has been stored in wood for at least three years. Some of the whisky evaporates through the wood during storage. About 1-2 percent of the whisky evaporates each year in a natural process which is called the ‘angel’s share’. Since the alcohol content must be at least 40 percent in order for whisky to be called whisky, this means that there is a theoretical limit to how many years a whisky can be stored before it has to be bottled. For example, if a whisky looses 1.5 percent of its alcohol content each year it may only be stored for 32 years before the alcohol content drops below 40 percent. Because of this it is unusual for whisky to be stored much longer than 30 years. Yet another reason for the limited maturation period is that whisky constantly picks up tannin from the wood, and too much tannin ruins the whisky. The greater part of all single malt whisky is stored between 8 and 12 years.
Before the whisky is bottled it is usually filled into large tanks to be cut with de-mineralised water to 40, 43 or 46 percent. Some bottlings are filled straight from the cask however, and are thus called ‘cask strength’ or ‘raw cask’. This whisky is best enjoyed with some water although most whisky will in fact benefit from a slight measure of water since it enhances both the flavour and the aroma of the whisky.
After the whisky is cut it is common to chill-filter it. This is done in order to remove slight impurities from the whisky which otherwise would cause a clouding effect at low temperatures. Not all distilleries practise chill-filtering since they believe that it removes some of the character of the stored whisky.
Most distilleries do not have their own bottling facilities and buy the service instead from specialised bottling plants. There are a few, however, such as Springbank, Glenfiddich and Bruichladdich who still do their own bottling on site –these also use the same spring water that is used during the production process when they make the final cut of the whisky.
Not all matured whisky are bottled and sold as official bottlings; it is for example possible for a private individual to buy their own cask at many distilleries. It is even more common for distilleries to sell some of their casks to independent bottling companies. Some of the larger independent bottlers are Signatory, Murray & McDavid, Cadenhead’s, Gordon and Macphail and Douglas Laing.