How whisky is made, from grain to cask
If you work in a whisky business and have never stood in a distillery, this is the walk through the building. Each stage below explains a number you will meet at your desk.
Whisky starts as a beer nobody drinks
The first half of making malt whisky is close to brewing. Grain is soaked in hot water, its starch turns to sugar and yeast turns that sugar into alcohol. What comes out of fermentation is a cloudy, unhopped beer of roughly 8% ABV. Distillers call it the wash.
The second half is what makes it whisky. The wash is distilled to concentrate the alcohol. The spirit then sits in oak casks for years. Most of the figures in a whisky company's reports, from production volumes to stock value, trace back to one of these stages.
Malting: getting barley ready to give up its sugar
Barley stores its energy as starch, which yeast cannot eat. Malting fixes that. The maltster steeps the grain in water, lets it germinate for several days so it builds up enzymes, then dries it in a kiln to stop growth. Most distilleries today buy malt from specialist maltsters rather than making their own.
If peat is burnt during kilning, smoke compounds called phenols settle on the grain. They survive distillation, which is where smoky whiskies get their character.
Grain whisky uses unmalted cereals such as wheat or maize. These are cooked to soften the starch, with some malted barley added for its enzymes. Scotch rules allow only the grain's own enzymes. Some other spirit categories permit added commercial enzymes.
Mashing and fermentation
The malt is milled into a coarse flour called grist and mixed with hot water in a mash tun. The first water goes in at about 64 °C, the range where the malt enzymes convert starch to sugar fastest. The sweet liquid, called wort, is drained off and the grain is rinsed with hotter water to collect what is left.
The wort is cooled and pumped into fermenting vessels called washbacks, made of wood or stainless steel. Yeast goes in. Over two to four days it produces alcohol, carbon dioxide and a range of fruity flavour compounds. Longer fermentations tend to give a fruitier spirit.
One difference from brewing: a distiller does not boil the wort. Some bacteria survive into fermentation and add to the flavour late on. A brewer would call that a problem. Here it is part of the house character.
Distillation: pot stills and column stills
Alcohol boils at about 78 °C and water at 100 °C, so the vapour from heated wash is richer in alcohol than the liquid. That is the whole trick.
Pot stills are large copper kettles run in batches. Scotch malt whisky is usually distilled twice. The wash still produces low wines of roughly 20 to 30% ABV. The spirit still takes those up to around 70%. During the second run the stillman makes cuts. The first part to come over, the foreshots, is too volatile and harsh. The last part, the feints, is oily and heavy. Only the middle cut, the heart, goes to the cask. Foreshots and feints are recycled into the next batch. Copper matters too, because it reacts with sulphur compounds and strips out meaty, rubbery notes.
Column stills run continuously. Wash goes in at one point and spirit comes off at another, hour after hour. They can reach far higher strengths and give a lighter spirit, which suits grain whisky and the neutral spirit behind vodka and most gin. Scotch must come off the still below 94.8% ABV, so a whisky column is never run all the way to neutral.
Maturation: where most of the time goes
Fresh spirit, called new make, is clear and fiery. It is usually reduced with water to a filling strength and put into oak casks. Scotch must spend at least three years in oak casks of no more than 700 litres, in Scotland. Bourbon must go into new charred oak containers.
In the cask the wood adds colour plus notes of vanilla, spice and dried fruit. The charred inner layer removes some harsh sulphur character. Air seeping through the staves slowly changes the spirit. Some liquid evaporates every year, which the trade calls the angels' share. Our guide to what the cask actually does goes deeper.
Blending, reduction and bottling
Most whisky sold anywhere is a blend of many casks, often of both malt and grain whisky. Our guide to malt, grain and blended whisky explains the categories. Casks chosen for a batch are emptied into a vat and mixed. The whisky is reduced with demineralised water to bottling strength, which for Scotch is at least 40% ABV. It is often chill filtered so it stays clear when cold. Scotch may add plain caramel colouring to keep each batch the same shade.
What this means at your desk
The process explains why whisky businesses behave the way they do. A litre distilled today cannot be sold as Scotch for three years. A 12 year old takes twelve. The production plan and the sales forecast run on different clocks. Volumes are counted in litres of pure alcohol rather than bulk litres, because the strength changes at nearly every stage.
A dashboard can show that stock of a 12 year old is falling. It will not tell you that the casks to replace it had to be filled years ago, by someone working from a forecast you never saw. Teams who know the floor ask better questions of their data.
Common questions
Is whisky just distilled beer?
Close. The wash is an unhopped, unboiled beer of about 8% ABV. Distillation and years in oak turn it into whisky.
Why is malt whisky distilled twice?
One run in a pot still does not concentrate the alcohol enough or separate the flavours cleanly. The second run lets the stillman choose which part of the spirit goes into the cask.
Where does smoky flavour come from?
Mostly from peat smoke absorbed by the barley while it is dried in the kiln. The smoke compounds carry through into the spirit.
How long does whisky take to make?
From mashing to new make takes less than a week. Maturation takes years: at least three for Scotch and Irish whiskey, often much longer.
Learning for yourself? See Craft Distilling
