How Single Malt Whisky is Made

A Detailed Description of Single Malt Whisky Production

How is Single Malt Whisky Made? For more than 500 years barley and water have been the basic ingredients for Single Malt Scotch Whisky. Besides their rugged beauty, the Scottish highlands are characterised by vast grain fields, especially during harvest season. Scotland has unique water. Since there is no limestone, the water is very soft. The rainwater flows over hillsides overgrown with heath and through peat meadows, thereby taking up the unique flavour typical for each distillery. Small, well-protected wells provide the water for the single malt Whiskies. But also the big rivers are needed for producing Whisky. They provide cooling water for the pot stills.

• Cultivation of Barley

• Malting the Barley

• Alcoholic Fermentation

• Scotch Whisky Distillation

• Filling the Casks

• Maturation in the Cask

• Bottling of Whisky

Cultivation of Barley

Single Malt Whisky is made exclusively from malted barley. Most of the barley used in Scotland is grown on the Scottish and English east coasts. The Lowlands, with their fertile fields and mild climate, offer ideal conditions for growing barley. Here, the light sandy soils and low rainfall ensure good yields. Some producers pride themselves on using only Scottish barley, but the barley grown in Scotland is not enough to meet the needs of the country's Whisky industry. So usually barley is imported from England or other parts of Europe (or even Canada). A basic distinction is made between winter barley (sown in autumn) and summer barley (sown in spring). The latter has a higher starch content, while the former has more protein, which is why summer barley is more commonly used for further processing in Whisky. A low nitrogen content (below 1.6%) is important for further processing, as this indicates proteins that make the Whisky more bitter. A high starch content, on the other hand (over 60%), is desirable because this is converted into sugar, which then ferments.

Malt to Flour

Malting the Barley

Alcohol is produced by fermenting sugar. The barley grain contains primarily starch. In chemical terms, starch is a multiple sugar (single sugar molecules forming chains). In order to release the sugar, the starch must be split into smaller sugars (maltose – malt sugar). Traditionally, the barley is steeped in water and left for germination on malting floors.

• The Drying of Malted Barley

After the barley grain has opened and the germ has reached approximately 2/3 of the length of the grain, the starch has turned into sugar. Now the germination process is interrupted by spreading the still wet barley on grids in the kiln and drying it with hot air from below. Drying is stopped at 4% humidity. This stage contributes significantly to the character of the Whisky. If you add peat to the fire, the malt gets a smoky peat note. The steam is discharged through the pagoda roofs of the distilleries.

Alcoholic Fermentation

How does the malted barley produce alcohol? Through the alcoholic fermentation in the washbacks. To get the wanted beer, also called wash, the malt has to take some steps.

• The Mashing of the Malt

The finished malt is milled to flour. This coarse flour is called grist and is mixed with hot water in the mash tun. If the grist is too coarse the sugar can't be fully extracted. If the grist is too fine it sticks together, and the sugar can also not be extracted completely. The malt is mashed three times before the sugar solution is cooled in a cooler. In the first run, the water has a temperature of about 65° C; in the second run, the temperature of the fresh water is increased to 80° C. For the final run, the water is heated nearly to the boiling point (95° C). During this third run, only so little sugar is extracted that this weak sugar solution is cooled down and used for the first run of the next batch. The remaining mash is brought to specialised plants where it is dehydrated and the residue is processed into animal feed. The exhaust air of these plants can be smelled for miles. The sugar solution must be cooled down to 20°C since the yeast wouldn't survive higher temperatures. Add a certain amount of yeast to the sugar solution.

• The Alcoholic Fermentation in the Washbacks

The resulting liquid is called wort. It is stored for two to four days in the wash backs until fermentation is finished. During alcoholic fermentation, the yeast strains convert the sugar into alcohol and carbon dioxide (CO2), an odourless and colourless gas. Beer breweries and large grain distilleries collect the CO2 for industrial use. Malt Whisky distilleries are usually too small to do that, except for Tomatin, who used to collect the CO2 from their more than 20 pot stills. The wash backs are covered with lids so no vinegar bacteria can enter and the wash back doesn’t boil over. In addition, the wash backs have a horizontally rotating blade that continually cuts the foam. The wash backs are usually made from Oregon pine or cypress wood, which is especially resistant to fungi. Recently also stainless steel has been used since it doesn’t have to be impregnated with chemicals or cleaned so much.

Fermentation is finished after approximately 48 to 96 hours. The “beer” – the Scots call it wash – then has an alcohol content of 8 to 9% and is ready to be filled in the stills.

Scotch Whisky Distillation

After the mash has been fermented and alcohol was created, the mash is filled into pot stills for distillation. In this process, the alcohol in the mash is further extracted.

DEGONG pot stills

• The Distillation in Pot Stills

The wash is filled into the first copper pot still, called wash still, and is heated from below and from the inside respectively. Today mainly hot steam is used for heating. Using an external gas flame has become rare. In the first case, hot steam is lead through specially shaped heating tubes inside the pot still, thereby heating the wash. At 78° C, the alcohol starts to evaporate before the water does. The alcohol steam rises in the tapered tube.

Over the neck and the lyne arm the steam is led into a condenser where the alcohol steam is liquefied again. The water mostly remains in the pot still. All Single Malt Whisky distilleries work with at least two series-connected pot stills. The first one, the wash still, distils the wash to 20% to 25% of alcohol. The resulting liquid is called “low wines”. The low wines are then transferred into the second pot still, called low wines still or spirit still, where they are distilled to an alcohol content of 65% to 70%. In the Scottish Lowlands, a lot of distilleries used to use a third still. This third pot still produced even purer alcohol at more than 75%.

• The Relation between Taste and Distillation

Important! Keep in mind that pure alcohol tastes only like alcohol. A Single Malt Whisky gets its taste from the heavier oils and fats and the lighter esters and other flavour carriers from the wash. The further you distil a Whisky, the more it will lose its individual character.

During distillation, the unique shape of the pot stills is the main contributing factor to the taste of a Whisky. A long and slim shape produces soft, pure alcohol, while a short, squat shape produces strong, intense flavours. The intensity of the heating is also important for the taste. If you heat too strongly, many accompanying substances and fusel oils will get into the Whisky, which will surely not be as smooth as if it had been distilled slowly. Typically the distillation process in the spirit still takes up between 4 and 8 hours.

Filling the Casks

In small distilleries, the distilled spirit is filled straight from the spirit receiver into the casks. Larger distilleries use an intermediate spirit receiver from which the Whisky is then pumped into a large collecting tank, the spirit vat, in which the individual batches are already vatted. This way individual taste differences between separate batches can be levelled out. Filling the casks is mostly done by hand. The spirit is filled in through the bunghole on the side of the cask, which is then sealed with a cork.

Maturation in the Cask

By law, Scotch Whisky, including blended Whisky, must mature in a cask for at least 3 years and one day. Single Malt Whisky is usually matured for 10 or more years. You rarely find younger single malts. Excellent single malt whiskies are matured for 12 to 21 years. Only oak casks are used since oak wood is breathable and durable. Softwood contains resin, which agglutinates the pores.

Bottling of Whisky

Filling Whisky with a spirits filling machine.