How Whisky Is Made
Every malt whisky follows the same path from barley field to bottle. Small choices at each step — how long to ferment, where to cut the spirit, which cask to fill — are what make one distillery taste nothing like its neighbour.
1. Malting
Barley is steeped in water, spread out to germinate for several days, then dried in a kiln to stop growth. Germination unlocks enzymes that will later turn starch into sugar. If peat is burned in the kiln, its smoke flavours the malt — see Peat, smoke and PPM. Most distilleries now buy malt from specialist maltsters; a few (Laphroaig, Bowmore, Springbank, Kilchoman, Balvenie, Highland Park) still malt some of their own on traditional floors.
2. Milling and mashing
The malt is milled into grist and mixed with hot water in a mash tun, usually in several waters of rising temperature. Enzymes convert starch to sugar, and the sweet liquid drained off is called wort. The spent grain, draff, goes to farms as cattle feed.
3. Fermentation
Cooled wort goes into a washback (wood or stainless steel) with yeast. Over roughly two to four days the yeast turns sugar into alcohol, carbon dioxide and a host of flavour compounds. The result is wash — essentially a strong, unhopped beer of around 7–9% ABV. Longer fermentations tend to give fruitier spirit.
4. Distillation
Malt whisky is usually distilled twice in copper pot stills:
- The wash still boils the wash to produce low wines, around 20–25% ABV.
- The spirit still redistils the low wines. The stillman makes the cut: the first runnings (foreshots) and the last (feints) go back for redistillation; only the heart — the middle cut — is kept.
The new-make spirit comes off at around 65–70% ABV and is usually reduced to about 63.5% before it goes into the cask.
5. Maturation
In the cask the spirit mellows and takes on colour and flavour from the wood for at least three years — often far longer. Each year a little evaporates through the wood: in Scotland about 2% a year, the angel's share. More on this in Casks and maturation.
6. Bottling
Casks are vatted together (or bottled singly), reduced with water to bottling strength, often chill-filtered and sometimes coloured — or not, which labels increasingly announce. Then it's yours.