How single malt Whisky is made

A detailed description of single malt whisky production

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Barley and water have been the basic ingredients for Scottish single malt whisky for more than 500 years. In addition to the rugged beauty of Scotland, the vast fields of grain, especially at harvest time, shape the character of the Scottish Highlands.

Scotland has incomparable water. As Scotland has no limestone, the water is very, very soft. The rainwater flows down the heather-covered hillsides and through peat meadows to the valley. In the process, it picks up its typical flavour for each distillery. Small, well-kept springs supply the water for the single malt whiskies. But the big rivers are also needed for whisky production. They supply the necessary cooling water for the stills.

The production of whisky is comparatively simple. The barley is left to germinate until the starch of the grain has become malt sugar. The malt is then kilned and coarsely ground. The sugar is leached out with hot water and the liquid is allowed to ferment. The result is a beer without the addition of hops. This beer is then distilled twice on copper stills, the pot stills. It goes into oak barrels for maturation before being bottled after three years at the earliest. High-quality single malt whiskies sometimes mature for decades.

The individual production steps are explained below:

  1. The cultivation of the barley
  2. Malting the barley
  3. Mashing
  4. Alcoholic fermentation
  5. Distilling (distillation)
  6. Filling the barrels
  7. Maturation in the barrel
  8. Bottling

If, after reading these pages, you think single malt whisky is a science in itself, enjoying it is nevertheless simple. Let your taste be your guide. Drink it neat, dilute it with soft water if necessary and never use ice or mineral or soda water. It would mask the incomparable taste of Scotland's national drink.

The 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 boast of 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 bought in from England or other parts of Europe (or 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 often 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.

Malting the barley

Alcohol is produced from sugar through fermentation. The barley grain initially contains mainly starch. Chemically, starch is a poly-sugar (individual sugar molecules linked into chains). In order to release the sugar, the starch must be broken down into sugar (maltose) by fermentation. According to the old tradition, the barley is soaked (steeping) and laid out on malting floors to germinate.

When the barley has a water content of 45% after soaking, the conversion of starch into sugar proceeds best. The barley must be turned by hand at precisely timed intervals so that all the grains germinate evenly. The germination process takes about 5 days. The most important distilleries that still malt their own barley include Balvenie, Bowmore, Highland Park, Laphroaig and Springbank. With the exception of Springbank, the other distilleries now only produce some of their own malt. Instead, most of the malt is sourced from modern drum malting plants.

After the barley grain has opened and the germ has reached about 2/3 of the length of the grain, the starch has become sugar. The germination process is now interrupted. To do this, the still moist barley is spread out on grates in the malt kiln and dried from below with hot air. The drying is stopped at 4% residual moisture. At this point, the later whisky also receives an important part of its character. If peat is added to the drying fire, the malt acquires a smoky peat note. The evaporated water vapour is discharged via the pagoda roofs of the distilleries, which are visible from afar.

Pagoda and pagoda roof

The picture of the Glen Garioch distillery shows the classic pagoda roofs. These can be seen on the buildings of many Scotch whisky distilleries. But what have these pointed, Asian-looking roofs got to do with a whisky distillery? A pagoda is actually a multi-storey tower whose individual storeys are usually separated from each other by ledges or eaves. This type of building is widespread, especially in Asia. At the end of the 19th century, this style was also fashionable in Europe and so Charles Chree Doig built Scotland's first pagoda at Dailuaine distillery in 1889. The pagoda roofs are found on the distillery buildings that contain the kiln, or malt floor. This is where the germinating barley was spread out and dried over the fire. Good ventilation is essential in this drying process, because the temperature in the kiln must not exceed 55 degrees Celsius so as not to destroy the enzymes in the grain. Today, the kilns with their typical pagoda roofs have mainly decorative purposes: only a few distilleries still malt their barley themselves.

The mashing

The finished malt is ground into malt flour, the grist, in a grain mill and mixed with hot water in the mash tun. The grist must not be too coarse. Otherwise not all the sugar will dissolve out. If the grist is too fine, it will stick together and the sugar will also not be able to dissolve 100% in hot water. Three times, the malt mash is leached out with water in the Mash Tun before the sugar solution is cooled down by a cooler. The first time, hot water with a temperature of about 65 °C is used. The second time, the temperature is already 80 °C. The last time, the temperature is raised to almost boiling temperature (95 °C). The third and last time, only so much sugar is dissolved that the weak sugar solution is left to cool a little and used for the first pass of the next batch. The water is removed from the leached mash in separate factories and the remaining mash is processed into animal feed. The exhaust air from these factories can be smelled for miles.

The alcoholic fermentation

The finished sugar solution - called word by the Scotsman - must have the heat removed down to 20 °C. The yeast does not survive much higher temperatures. To about 15,000 litres of sugar solution, 50 kg of special yeast cultures are added.

The resulting liquid is stored in large wooden vats called wash backs for the next two to four days until fermentation is complete. During alcoholic fermentation, the yeast strains convert the sugar into alcohol and carbon dioxide (CO2), an odourless and colourless gas. In beer breweries and large grain distilleries, the resulting CO2 is captured for industrial use. This is not the case with malt whisky distilleries, which are usually too small for this. An exception was made in earlier times by Tomatin, which collected the CO2 from its more than 20 stills.

The wash backs are fitted with lids to prevent vinegar bacteria from entering and to prevent the fermentation foam from overflowing. In addition, the wash backs have a large, horizontally running propeller at the top, which repeatedly beats the foam into small pieces. The fermentation vats are usually made of Oregon pine or cypress, as these woods are particularly resistant to fungi. More recently, stainless steel has also been used as a material, as this does not need to be impregnated or cleaned so much with chemical agents.

When fermentation is complete after about 48 to 96 hours, the 'beer', the Scots call it'wash', has an alcohol content of about 8 - 9% and can be fed into the stills.


The wash is filled into the first copper still, the pot still, and heated from below or inside. The heating is mainly indirect with superheated steam, more rarely with an external gas flame. In the first case, highly heated steam is passed through specially shaped heating pipes inside the pot still. This heats the surrounding wash. At a temperature of 78 °C and above, the alcohol begins to boil in front of the water. The alcohol vapour rises upwards in the tapering pipe.


Benromach still
Benromach still

The vapour is fed via the neck and the connecting pipe (Lyne arm) into a condenser, which liquefies the alcohol vapour again. Most of the water remains in the pot still. All single malt whisky distilleries work with at least two pot stills in series. The first pot still, the wash still, distils the alcohol to about 20 to 25 % alcohol by volume. The resulting intermediate product is called low wines. The low wines are then fed into the second still, called the Low Wines Still or Spirit Still. Here, alcohol with 65 to 70 % vol. is produced. In the Scottish Lowlands, it was widespread to place another still after the Low Wines Still. This third still produces even purer alcohol with an alcohol content of over 75 % vol. Today, there are only very few producing distilleries in the Lowlands (Ailsa Bay, Auchentoshan, Bladnoch, Daftmill, Glenkinchie), of which only Auchentoshan still has three stills.

Important! When distilling, it is important to note that pure alcohol only tastes like alcohol. A single malt whisky only tastes like whisky because it contains heavier oils and fats as well as light esters and other flavours from the wash. The higher you distil a whisky, the more it loses of its individual character.

The specific shape of the pot stills is primarily responsible for the flavour of the resulting whisky during the distilling process. A long slender shape produces a soft pure alcohol (e.g. Glenmorangie), whereas a short squat pot still produces a strong intense flavour (e.g. Lagavulin). The intensity of the heating is also important for the taste. If you heat very strongly, a lot of accompanying substances and fusel oils are driven out of the wash. The whisky will certainly not turn out as smooth as a slowly heated one. A typical normal and careful distillation process takes several hours (4 to 8h) in a Spirit Still.

Wash Stills usually hold between 20,000 and 30,000 litres, whereas Spirit Stills only hold 10,000 to 20,000 litres of the more concentrated Low Wines.

After 15 to 25 years, when the wall thickness of the copper has decreased to 4 to 5 mm, the pot stills have to be replaced. The stillman takes great care to ensure that the shape of the still is not altered and that there is no change in taste.

It is even said that dents and dings in the stills are taken over by the stillmen into the renewed stills. But this belongs to the realm of fairy tales.

The important task of the Stillman

The outlet side of the stills is sealed by the state so that no untaxed spirit finds its way into the thirsty throats of the Scots. However, in order to be able to assess the quality of the low wines and the spirit, the lines are passed through glass boxes, the so-called spirit and sample safes. In these safes, usually made of polished brass and glass, the stillman can examine the quality of the distillate and use valves and levers to direct the flow of liquid back into the still or into the spirit receivers.

All this is done by visual inspection and measuring instruments alone. A stillman cannot sample! In the sample compartment of the safe he can measure the temperature and take samples on which he can determine the density of the distillate and thus the alcohol content with spindles (hydrometers). It is important that the stillman cleanly cuts out the so-called middle cut and feeds it to the spirit receiver. This timely conversion is the stillman's most important task. It decides decisively whether the batch will be only good or excellent. It takes about 30 minutes for the pre-cut to run through. Then the middle cut is taken off for about 3 hours. The subsequent after-run is fed back into the Spirit Still. It contains higher concentrations of propanol, isopropanol and fusel oils.

The first distillate from the pot still could theoretically contain the highly volatile and poisonous methyl alcohol (methanol), which leads to blindness and even death if consumed in abundance. However, today's modern yeasts have all been bred not to produce methyl alcohol. The separation of the forerun thus only has a taste character. The finish from the pot still contains the fusel oils that are responsible for the headache. Since the after-run is stopped quite early in single malt whiskies, almost no people tend to get headaches after drinking single malt whisky.

The filling into barrels

Distilleries use different sized casks for storage. These are the most common: 1 Quarter Cask = 125 litres 1 Barrell = 158 litres 1 American Standard Barrel (ASB) = 200 litres 1 Hogshead = 250 litres 1 Butt = 500 litres Rarely, so-called Pungeons or Puncheons or Pipes with (600-700 litres) are used. With the filling of the water-clear and colourless raw whisky into barrels, the production of the single malt whisky is completed. This is followed by maturation in the cask store.

By law, Scotch whisky must be matured in casks for at least 3 years and one day. Cheap blends are rarely matured for more than the minimum period. Single malt whisky is usually matured for 10 years or longer. Only rarely do you find single malt whiskies that have been stored for a shorter period. Very good single malt whiskies mature for a long 12 to 21 years. Storage is always in oak casks, as only oak wood is breathable and sufficiently durable. Softwood, for example, contains resin and clogs the pores.

The origin of the barrels is of decisive importance for the later whisky taste. Most distilleries store their whiskies predominantly in American bourbon barrels. These barrels were made from American white oak and have already been used once for storing bourbon whisky. Many distilleries like The Macallan or Bowmore, on the other hand, rely on casks that were previously used to mature Spanish sherry or another wine. It is important that the casks are always made of oak. Legendary is a malt from Springbank that was stored in rum casks from the Caribbean and took on a greenish colour.

Somewhat less important for the later taste of the whisky is the storage location. The old warehouses are large dark warehouses with rammed floors. The casks lie on oak beams and are stacked between 3 and 6 levels above each other. Modern warehouses, on the other hand, have a concrete floor so that forklifts can be used to move the whisky casks. Until around the turn of the millennium, so-called racked warehouses, i.e. warehouses with steel shelves, were built to hold the horizontal casks. Today, the new whisky casks are usually stored upright on pallets.

Whisky in the Highlands matures differently from whisky on the islands, as the Highlands have hot summers and cold, snowy winters, whereas the Gulf Stream keeps the climate on the islands and directly on the coast very mild. This difference in weather has an influence on the ripening process.

Evaporation during cask ageing: The Angels' Share

When the whisky is still filled into the casks, usually with an alcohol content of 63.5%, a small part of its content constantly evaporates through the cask wall. Since alcohol is lighter and more volatile than water, more alcohol than water evaporates during the storage period. This causes the alcohol content to drop by 0.2 to 0.6 percentage points per year. This evaporating portion is called Angels' Share by Scots. The decrease in the amount of liquid is about two percentage points per year. The liquid decrease is controlled by a wooden measuring stick that is inserted through the filler opening. The rod has four scales on its four sides, which are intended for the four different barrel sizes. The scales show the target level for the elapsed number of years. This measuring method makes it easy to detect small leaks in barrels. The experienced inspector taps the ends of the barrels with a wooden hammer with a long handle and can conclude the fill level of the barrels from the resulting sound.

Evaporation on the one hand and flavour absorption from the cask wall on the other cause whisky to become softer in flavour with each passing year of maturation. The casks are tasted at regular intervals to find the exact moment when the whisky has reached its peak. The size of the cask also has an influence. Large casks have a relatively smaller inner surface area in relation to their contents. The absorption of flavour from the cask wall is therefore naturally less. Whisky in large casks must therefore be stored longer to achieve the same degree of maturity!

Casks are regularly reconditioned in the cask-making factories, so that some casks are used several times and for decades. It is natural that the whisky from a sherry cask used for the second time for storing whisky will pick up less sherry flavour than in a fresh one. Through these many different influences, an individual whisky is created in each cask over time.

Marriage by the Master Blender

Aberlour Distillery Cask Store
Aberlour Distillery Cask Store

But to ensure that a 16-year-old Lagavulin, for example, always tastes the same, the distillery has to blend its own single malts in such a way that the desired taste is always the same. This is where the master blender comes in. This person now has the task of combining the casks in such a way that the ideal aroma and a round taste are created. With standard bottlings, it is also important that the taste remains constant over the years. Often, the individual barrels are put together according to a standard recipe so that the right thing always comes out in the end. Of course, such a semi-automatic barrel selection is not the measure of all things. But it does help with the work of fine-tasting later on. Certainly, all blenders do this in their own way. How exactly remains their secret. One thing is certain, however: blending whisky is a creative art. This process has nothing to do with a blended malt, as all whiskies come from the same distillery. Almost all single malt whiskies from Scottish distilleries are bottled as a blend of several casks. However, only a blend of malts of different ages from a single distillery is permitted if you want to use the term single malt whisky on the bottle. The age of the whisky indicated on the bottle refers to the youngest whisky contained in the bottle.

If you would like to read about cask maturation in detail, we recommend the expert article.

The bottling

Only the Glenfiddich, Springbank and Bruichladdich distilleries have their own bottling facilities. All the other distilleries transport their casks, or the blends they have already made, by lorries and tankers to the large bottlers in Glasgow, Edinburgh or Perth. As a rule, around 30,000 to 60,000 bottles of the common single malt whiskies are bottled in one batch. The exact quantity depends on the transport volume of the trucks. Sales of these bottles are not yet so high that an automated bottling line would be profitable just for a single single malt whisky bottle. This is reserved for the big blended whiskies.

A speciality among the bottlings are the pure cask bottlings from predominantly independent bottlers such as Signatory Vintage, Gordon & MacPhail or Douglas Laing. These companies have their own whisky casks filled with fresh malt at distilleries and store them under their own supervision. Afterwards, they are bottled cask-clean. Each of these bottles contains a pure, unique single malt whisky.

The bottles are labelled with the name of the distillery, the type of cask used, the distillation and bottling dates, and sometimes with the cask and bottle number. Similar to wine, in this way you get single malt whiskies that taste different from year to year, even from cask to cask. The alcohol content also varies greatly. Often the alcohol content is reduced to 46%, 43% or 40% to make it milder and immediately drinkable. In single cask bottlings, the alcohol content is often left natural. In this case, it is called cask strength.

Independent bottlers pride themselves on simply filtering the malt whisky to remove wood chips before bottling. Other bottlers, on the other hand, swear by good chill filtration to remove all suspended particles completely. However, the actual influence on the taste of the whisky is unclear.

These different possibilities also result in different characters of the whiskies simply due to the way they are bottled. This is particularly interesting for experts.

If you want to read more about the independent bottlers in detail, you will find several articles and videos in the following section. We also have an article about a bottling plant from the inside for you.