Scotland’s whisky distilleries all have their own slightly unique approach to producing whisky, creating a style of spirit that is individual. The type of barley used, water sources, terroir and the still shapes are just some of the factors contributing to a distillery’s distinctive style of spirit. However, the main process of making Single Malt Scotch Whisky is fairly universal and can be broken down into the seven stages outlined below.
The Seven Stages of Whisky Production
One of the three key natural ingredients used in the making of Single Malt Scotch Whisky is malted barley. The first step in producing malted barley involves soaking the grain in water to raise the moisture content and start germination (this process is known as ‘steeping’). During the germination process, starch stored in the grain converts into sugars, a key ingredient for creating alcohol during the latter stage of fermentation.
In the traditional malting process, once the steeping has been completed, the barley is then spread out on a malting floor while germination continues. The steeped barley is turned regularly using a malt shovel, to prevent the grains’ rootlets from knotting together.
Top: dried barely before it has been steeped. Bottom: barley with rootlets that have begun to germinate after steeping.
After 3 – 4 days on the malting floor, germination is halted to prevent the grain using up all the stored sugars for growth. This is done by drying the germinated barley to reduce the moisture content through gently heating the grain in a kiln – a process known as kilning.
One of the most recognisable characteristics of some Single Malt Scotch Whiskies is created during the kilning process. The distinctive smoky flavour, often associated with Islay malt whiskies, is created by drying the malt, using peat to flame the kiln fires. The smoke created through burning peat in the kiln is transferred to the drying barley; this smoky characteristic is then present in the final spirit. Distilleries which use peated malt in their distillation process are in the minority; far more use malt that has been dried using more neutral heat sources, to produce a whisky with a less smoky character.
Top : The heating floor above kiln. Bottom: The distinctive distillery pagoda roof (chimney) and a coal fired kiln.
Milling is the process by which the malt barley is prepared to be mixed with water to extract the sugars. First, the malt is screened to remove any unwanted elements, such as stones and leftover green shoots. After this, the barley is crushed in a mill to create a mixture called ‘grist’ (a very coarse flour). The grist must be milled to exactly the correct consistency to prevent problems during the next stage of production, the mashing process.
Although there is slight variation between distilleries, the desired consistency of grist is generally a ratio of approximately 65% grits (known also as middles), 25% husks and 10% flour. This ratio is the right balance to extract an optimal amount of sugars from the malt, while not allowing the Mash Tun to become clogged with too much flour.
Malt after it has been milled into grist (65% grits, 25% husks and 10% flour).
The second key ingredient in whisky production is added during the Mashing stage – water. The water added at this stage is invariably sourced from a local spring and has an important influence on the whisky’s final character. The milled malt, or grist, is mixed with hot water (approximately 65°C) in a large, metal vessel known as a Mash Tun. The solution, known as Wort, is then strained through grills at the bottom of the Mash Tun, leaving the grist behind. This process is repeated using the same grist three more times at increasingly hot temperatures. This ensures that all the sugars have been extracted from the malted barley. The leftover exhausted grist is collected and used for cattle feed, known as Draff.
Hot water being poured into a Mash Tun to make the Wort.
Once the Wort has been extracted from the Mash Tun, it is cooled and enters the washbacks (large wooden or steel vats). The third key ingredient is then added – yeast. The addition of yeast starts the fermentation process, through which the sugars in the Wort are converted to alcohol. The Wort is fermented in the washbacks for anything between two and four days, depending on the distillery, during which time many of the whisky’s distinctive aromas and flavours are created. The end result of fermentation is an alcoholic liquid called Wash, similar to a strong beer, which is approximately 8% ABV.
Fermenting Wort in a Washback.
Single Malt Scotch Whisky is distilled in vessels made from copper, known as Pot Stills. The shape and size of these varies between each distillery and has an influence on the final style of the spirit. Most distilleries in Scotland use two pot stills to produce Malt Whisky, while a few use a triple pot still system for a lighter character.
The Wash Still
Initially the wash created during the Fermentation stage is pumped into the first copper still, known as the Wash Still. The Wash Still is then heated until vapour begins to travel up the neck of the still. The vapour cools at the top of the still and travels along tube known as the Lyne Arm. The vapour then condenses back into liquid in a cooling tank known as a condenser (either a Shell and Tube or Worm Tub).
In order to prevent the wash from boiling over the neck of the wash still, the temperature is carefully controlled by the still operator, who observes the activity of the wash through windows in the side of the stills.
The distilled wash, now referred to as Low Wines, has a strength of approximately 20% ABV, passes through the Spirit Safe into a storage vessel called the Low Wines and Feints Receiver. However, it still contains many impurities and is quite a low alcoholic strength, so requires further distillation.
Copper Stills vary in both shape and size and this will have an effect on the characteristics of the final distilled spirit.
The Spirit Still
The distilled wash or Low Wines are then charged into the second copper still, the Spirit Still, for the final distillation. The distillation process is repeated and the Low Wines are then heated until they vaporise and travel up the neck of the Spirit Still. There are three parts to this distillate: Foreshots, Heart and Feints.
Foreshots: The Foreshots are too overpowering to be used in the final spirit so are siphoned off and mixed back into the Low Wines and Feints receiver for the next batch to be charged in Spirit Still again.
Heart: Once the Foreshots have run through, the best cut of the distilled spirit – the Heart – begins to flow. Once this finest part of the distillate is flowing, the still operator switches the flow of liquid to the Spirit Receiver. This best cut of the distillate will be kept, matured in oak casks and eventually sold as Single Malt Scotch Whisky. The strength of the Hearts is generally around 75% ABV at the beginning of the run. Once it has dropped to around 60%, the still operator switches the flow of liquid away from the Spirit Receiver.
Feints: This end cut of the run is known as the Feints. It has an overpowering characteristic, while being too low in alcoholic strength to be used for maturation. It is therefore mixed with the next batch of Low Wines and Foreshots, to be charged back into the Spirit Still for the next distillation.
The spirit safe controls the flow of distillate to either the Low Wines Receiver or the Spirit Receiver.
Overall, only approximately 15% of each distillation run is used as the final spirit to be matured into whisky. This small, prized heart of the distillation run is transferred into oak casks for maturation at a high strength. It is known as New Make Spirit until it comes of age.
To be classed as Scotch Whisky, New Make Spirit is required by law to be matured in oak casks, in Scotland, for a minimum of three years. Most is matured for much longer, to further improve the character.
Once a cask of whisky is laid down in a warehouse it is sampled periodically until it is deemed ready to bottle. At this point, it is either blended with grain whisky to make a Blended Scotch Whisky, married together with other whiskies from the same distillery to make a large batch of Single Malt Scotch Whisky, or, as Claxton’s do, preserved with its individual characteristic by filling bottles directly from only one cask to create Single Cask Single Malt Scotch Whisky.
Oak casks of New make Spirit are laid down to mature for a minimum of three years before they can be called Scotch Whisky.
The maturation process is perhaps one of the most varied, complex and important stages in the production of Single Malt Scotch Whisky. In fact, it is widely recognised throughout the industry that the cask in which a whisky matures contributes the majority of its final character. The flavour and aroma of a whisky can be greatly influenced by many factors of cask maturation.
Cask maturation is a wonderfully interesting and hugely important stage of whisky production. To discover more about the impact of maturation in different styles of casks, visit the Cask Influence section.
Left: A range of cask maturing in a traditional earthen floored warehouse (Dunnage Warehouse). Right: A large pile of empty ex-bourbon barrels waiting to be filled with New Make Spirit.