How Does a Still Work?

A still separates alcohol from a fermented liquid by heating it until alcohol vapour rises and boils off before water does, then cooling that vapour back into a concentrated liquid.

Distillation relies on one basic fact: alcohol boils at a lower temperature (around 78°C) than water (100°C). A still is built to exploit that difference.

The basic process

1. Heat the wash — the fermented liquid (a low-alcohol "beer" or "wine," depending on the base ingredient) is heated in the still.
2. Vapour rises — as the temperature climbs past alcohol's boiling point but stays below water's, alcohol vapour (along with some water vapour and other volatile compounds) rises up through the still.
3. Vapour travels through the still's neck/column — on the way, it can pass through elements like a rectifying column or copper contact surfaces that further refine which compounds pass through.
4. Condensation — the vapour then passes through a condenser (often a coiled copper pipe cooled by water), where it cools back into liquid form — now a much higher-alcohol spirit than the wash that went in.
5. Collection — this condensed spirit is collected, and the distiller manages the run in stages (see "What are heads, hearts and tails?") to select the best-quality portion.

Why copper matters

Most stills are made of copper, which isn't just tradition — copper reacts with and removes certain sulphur-based compounds produced during fermentation that would otherwise create unpleasant, eggy or rubbery off-flavours in the final spirit. More copper contact generally means a cleaner spirit.

Two broad still designs

• Pot stills — batch-based, retain more character and congeners, typical of whisky, cognac and many rums.
• Column stills — continuous, produce a lighter, more highly rectified spirit, typical of vodka, gin's neutral base, and grain whisky.

See "What is pot distillation?" and "What is column distillation?" for a deeper look at each.