How Single Malt Whisky is made

How Single Malt Whisky is made - bottles

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.

1. Cultivation of Barley
2. Malting the Barley
3. Alcoholic Fermentation
4. Scotch Whisky Distillation
5. Filling the Casks
6. Maturation in the Cask
7. Bottling of Whisky

How Single Malt Whisky is made - Cornfield

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. Barley varieties that meet these requirements and are therefore mostly grown for Whisky production are Optic, Concerto, Belgravia, Propino, Quench and Shuffle. Meanwhile, new barley varieties are continuously cultivated to ensure the highest possible yields.

Malt to Flour
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.

Classic Malting Floor - Glendronach
Classic Malting Floor - Glendronach

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.

Kiln of Glen Garioch
Kiln of Glen Garioch

Pagoda and Pagoda Roof

In the picture of the Glen Garioch Distillery, you can see the classic pagoda roofs very well. These can be seen on the buildings of many Scottish Whisky distilleries. But what are these pointed, Asia-looking roofs doing on a Whisky distillery? A pagoda is actually a multi-storey tower, whose individual floors are usually separated from each other by cornices or eaves. This way of building is especially widespread in Asia. At the end of the 19th century, this style was also modern in Europe and so Charles Chree Doig built Scotland's first pagoda in 1889 at the Dailuaine Distillery. The pagoda roofs can be found on the distillery buildings, which contain the kiln, i.e. the malt floor. Here, the germinating barley was spread out and dried over a fire. Good ventilation is essential in this drying process, as the temperature in the kiln must not exceed 55 degrees Celsius in order not to destroy the enzymes in the grain. Today, kilns with their typical pagoda roofs have mainly decorative purposes: only a few distilleries still malt their barley in-house.

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. 50kg of yeast are added to 15,000 litres of sugar solution.

Washback- Glenkinchie
Washback- Glenkinchie

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.

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%. Today there are only a few distilleries left in the Lowlands (Ailsa Bay, Auchentoshan, Bladnoch, Daftmill and Glenkinchie), and only Auchentoshan still has three pot stills.

Whisky distillation - The pot stills of Glenfiddich
Whisky distillation - The pot stills of Glenfiddich

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 (e.g. Glenmorangie), while a short, squat shape produces strong, intense flavours (e.g. Lagavulin). 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.

The wash stills usually have a capacity of 20,000 to 30,000 litres, while the spirit stills can only contain 10,000 to 20,000 litres of the higher concentrated low wines.

Whisky distillation - the spirit safe of Auchentoshan
Whisky distillation - the spirit safe of Auchentoshan

The important Job of the Stillman

The pot stills must be replaced after 15 to 25 years when the wall thickness of the copper has decreased to 4 to 5 mm. The stillman makes sure that the shape of the still is not changed because this would lead to a change in taste, too.

The story goes that some stillmen even replicate dents and bumps in the new pot stills, but that’s just a fairytale. The outlets of the stills are sealed by the government so no thirsty Scot can get his hands on untaxed spirit. In order to assess the quality of the low wines and the spirit anyway, the pipes are run through a case usually made from glass and polished brass, the spirit and sample safe. The stillman checks the quality and runs the spirit back into the still or into the spirit receiver using valves and levers.

All this is done only by visual inspection and with measuring instruments. A stillman cannot taste the spirit! In the sample compartment of the safe he can measure the temperature and take samples in order to measure the density of the spirit (and its alcohol content) with hydrometers. The stillman’s most important task is to cut off the middle cut properly. At this stage, it is decided whether the batch is going to be just good or excellent. The foreshots take about 30 minutes to run through. The middle cut is then extracted for about 3 hours. The last runnings of the distillation, called feints, are led back into the spirit still. They contain higher concentrations of propanol, isopropanol and fusel oils.

The foreshots might contain the highly volatile and poisonous methanol, which can lead to blindness or even death if consumed excessively. Modern yeast strains are grown not to produce any methanol at all. That’s why the separation of the foreshots is just a matter of taste today. The feints contain the fusel oils responsible for headaches. Since the feints are cut off rather early, people usually don’t get headaches after enjoying Single Malt Whisky.

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.

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Filling the casks: regulation

After the casks are filled, they are weighed to estimate the tax, which has to be paid. Then they are transported (or sometimes simply rolled) into the warehouse, where they stay at least for three years. By law, each cask must be marked with a unique number, the name of the distillery and the distillation year. This used to be done with a template and a paintbrush. However, in recent years more and more distilleries have begun to use barcodes readable only by computers. What a shame!

The Cask Sizes

There are differently sized casks for the maturation of Whisky:

  • 1 Quarter cask = 33 us. gal. (125 Litres)
  • 1 Barrel = 41.7 us. gal. (158 Litres)
  • 1 ASB = American standard barrel = 52.8 us. gal. (200 Litres)
  • 1 Hogshead = 66 us. gal. (250 Litres)
  • 1 Butt = 132 us. gal. (500 Litres)
  • Pungeons (or puncheons) and pipes 158,5 – 184,9 us. gal.; (600 – 700 litres) are used only rarely.

More about the different types of casks here.

Filling the crystal-clear new make into casks is the last step in the active production of Single Malt Whisky. Following is the maturation and bottling, which can be more described as the processing of the produced Whisky.

For more details about Whisky casks, visit this site.

Filling of Casks at Glenturret
Filling of Casks at Glenturret

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.

The Development of Taste during Cask Maturation

The origin of the casks is crucial for the taste of the Whisky. Glenfiddich predominantly matures their Whiskies casks made from American white oak that has previously been used to mature Bourbon Whiskey. In contrast, distilleries like Macallan or Bowmore use mainly casks that held Spanish Sherry before. One Malt Whisky from Springbank became a legend: it was matured in ex-rum casks from the Caribbean and took on a green colour.

A bit less important for the taste of the Whisky is the place of maturation. The old warehouses are dark and have earth floors. The casks are stored on oak beams and are stacked on top of each other in 3 to 6 rows. Modern warehouses have concrete floors so the casks can be moved with forklifts. Until the end of the last century, the casks were stored lying on steel racks. Nowadays the casks are mostly stored upright on pallets. Whisky matures differently in the highlands than on the islands, since there are hot summers and cold, snowy winters in the highlands, while the gulf stream provides for a mild climate on the islands and at the coast.

Maturation - Casks in the Ardbeg Warehouse
Maturation - Casks in the Ardbeg Warehouse

The Angel’s Share During Maturation

Usually, the Whisky is filled into the cask with an alcohol content of 63.5%. Over the years some of the cask content evaporates through the cask walls. Alcohol is more volatile than water so it evaporates more quickly. The alcohol content of the Whisky decreases by 0.2% to 0.6% annually. The Scots call this evaporated alcohol the Angel’s Share. The fluid level decreases by 2% each year. It is measured with a square wooden ruler that has four scales on each of its four sides corresponding to the various cask sizes. The scales indicate the target level for each year. With this method, even the smallest leaks can be detected. Experienced controllers tap on the cask ends with a long-handled wooden hammer and deduce the fluid level by the resulting sound. Due to the evaporation and the absorption of flavours from the cask wood, the Whisky becomes mellower each year. Samples are taken regularly from each cask to find out when the Whisky has reached its prime. The size of the cask is important, too. Larger casks have a smaller surface in proportion to the content, and fewer flavours can be extracted from the wood. Therefore Whisky in large casks must be stored longer in order to reach the same level of maturation!

Casks are regularly refurbished in cooperages. Some casks are used several times and over decades. Of course, Whisky absorbs fewer sherry flavours in a second-fill sherry cask than in a first-fill cask. Through these various influences, each cask produces an individual Whisky over time.

The Master Blender

But to ensure that, for example, a 16-year-old Lagavulin always tastes the same, the distillery must combine its own Single Malts in such a way that the same desired taste is always produced. This is where the Master Blender comes in. This person has the task of combining the casks in such a way that the ideal aroma and a round taste is created. For standard bottlings, it is also important that the taste remains constant over the years. The individual casks are often put together according to a standard recipe so that the right product always comes out in the end. Of course, such a semi-automatic cask selection is not the measure of all things. But it helps in the work of the later fine-tuning. Surely all blenders do this in their own way. How exactly they do it is probably their secret. But one thing is certain: Whisky blending is a creative art. This process has nothing to do with Blended Malt, as all Whiskies come from the same distillery. Almost all Single Malt Whiskies from the Scottish distilleries are bottled as a mixture of several casks. However, only the blending of Malts of different ages from a single distillery is permitted if the designation Single Malt Whisky is to be used on the bottle. The age of the Whisky indicated on the bottle refers to the youngest Whisky contained in the bottle.

For those who want to read in detail about the maturation in the cask, we recommend this expert article.

Bottling of Whisky

How is the Whisky filled into the bottles? Only Glenfiddich, Springbank and Bruichladdich have their own bottling plants. All other distilleries ship their casks to the big bottlers in Glasgow, Edinburgh or Perth.

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Example for Bottling: Scottish Liqueure Center

The Scottish Liqueure Center is a small bottler near Perth. It is one of the bottlers, where the distilleries send their casks, in order to bottle them. The first step is the batting tank, where cask(s) are being mixed in order to have the same taste and aroma in one bottling. The Whisky is then transferred through tubes to the bottling station where the machine is filling the Whisky into single bottles. Before the bottles are filled, they are washed out with the same Whisky, that gets filled into it.

After the bottles are filled they are brought to the corking machine. Here the machine is putting the corks in and tightens them. Is the bottle closed, the label is being put on. In the last step, the capsule is being put on, above the cork, to seal the bottle of Whisky. Then the bottles are placed on palettes and are ready for being shipped.

Also interesting is the storage of the casks, which are brought by the distilleries. Those are being checked for their mass of spirit. A rod is put into the cask via the bunghole. With that, two points are measured: The ‘height’ of the spirit, and the height of the cask. With the difference between those two points, it can be said, how much spirit is in the cask. The scale on the rod is not linear, since the sides of the casks is round.

Bottling at Signatory Vintage
Bottling at Signatory Vintage

The Independent Bottlers

Usually, between 30,000 and 60,000 bottles of the standard Single Malt Whiskies are bottled in one batch, depending on the capacity of the freight vehicle. Sales aren’t high enough so that an automated bottling line for every single Single Malt Whisky would be profitable. This remains reserved for the big blended Whiskies.

The cask bottlings of the Independent Bottlers such as Signatory Vintage, Gordon & MacPhail or Douglas Laing are something special. These companies buy newly made Malt Whisky from the distilleries and then mature it on their own. Afterwards, they bottle the Whisky straight from the cask. Each of these bottles contains a really pure, one-of-a-kind Single Malt Whisky.

The bottles are usually labelled with the name of the distillery, the cask type, distillation and bottling date, and sometimes with the cask and bottle number. Similar to Wine, these Single Malt Whiskies taste differently from year to year, or even from cask to cask. Also, the alcohol content can vary greatly. Sometimes it’s reduced to 46%, 43% or 40%, sometimes the Whisky is bottled at natural cask strength.

The Independent Bottlers are proud to only filter their Whiskies for splinters. Other bottlers use chill-filtration in order to get rid of all the floating particles. The bottling method thus contributes to the unique character of a Whisky.