How a Coffey still makes grain whisky

Two columns instead of one pot

Aeneas Coffey, a former Irish excise officer, patented his continuous still in 1830. It has two columns standing side by side. The first, the analyser, strips alcohol out of the fermented wash. The second, the rectifier, concentrates that alcohol into strong spirit.

A pot still works in batches: fill it, boil it, empty it, clean it, start again. A Coffey still keeps going for as long as wash and steam are fed in. That one difference explains why grain whisky is made in such large volumes and why it costs less to make than malt whisky. Our guide to pot still versus column still compares the two side by side.

What goes into the still

Grain whisky is usually made mostly from wheat or maize, with a share of malted barley to provide the enzymes that turn starch into sugar. The grain is cooked to break open its starch, mashed with the malt, cooled and fermented to a wash of around 8% ABV. Unlike a malt distillery, a grain distillery often sends the whole wash, grain solids and all, towards the still.

Before it goes into the analyser, the cold wash is piped through a coil inside the rectifier. That coil does two jobs. It cools the rising alcohol vapour, helping it condense. It also warms the wash on its way in, so less steam is needed later. It is a neat bit of energy saving for a design almost two hundred years old.

Inside the analyser

The hot wash enters near the top of the analyser and trickles down over a stack of perforated plates. Live steam is blown in at the bottom and rises up through the plates. On each plate the steam meets the wash and strips out some of its alcohol.

By the time the wash reaches the bottom, almost all its alcohol has gone. What drains out is spent wash, a hot mix of water, grain solids and yeast. The steam leaving the top of the analyser is now a vapour rich in alcohol. It is piped across to the bottom of the rectifier.

Inside the rectifier

In the rectifier the alcohol vapour rises again through more plates. At every plate some vapour condenses and some re-boils. Each step concentrates the alcohol a little more and pushes heavier compounds down. The cold wash coil running through the column keeps that process going.

Near the top sits the spirit plate, where strong spirit is drawn off. Grain whisky from a Coffey still usually comes off at around 94% ABV. Scotch whisky rules say spirit must be distilled to less than 94.8% ABV, so that it keeps some flavour from its raw materials. Lighter compounds escape from the very top. Heavier ones, the fusel oils, are drawn off lower down and the liquid at the base is fed back into the analyser.

Why grain whisky tastes light

Spirit at 94% ABV carries much less of the fruit, cereal and oily character than pot still spirit at 70% ABV. That does not make it neutral. New make grain whisky still has a sweet, creamy, cereal and sometimes floral note. Long maturation in good casks turns it into a soft, vanilla rich whisky.

Most grain whisky ends up in blends, where it gives body and smoothness and lets the stronger malts show without shouting. Some is bottled as single grain whisky. Try one next to a blend and a single malt and you will start to notice what grain brings to the mix.

Coffey stills and India

Column stills are not new to India. Most Indian whisky is based on spirit from column stills, much of it from molasses rather than grain. The difference between grain spirit and molasses spirit matters for labelling rules in many export markets, which is one reason more Indian producers now talk about grain based whisky. Our guide to molasses versus grain spirit in India explains it.

Indian rules for what can be called whisky differ from Scotch rules and can change, so if you are buying for a brand rather than a glass, check the current notification.

Tasting the difference at home

Next time you have a single grain and a single malt from the same country, pour a small measure of each. Add a few drops of water to both. Nose the grain first: look for vanilla, cream, cereal and light fruit. Then nose the malt and notice how much more is going on in the fruit and texture. Drink water between them, keep the measures small and never drink and drive. That simple side by side tasting teaches you more about stills than any diagram.

Common questions

Who invented the Coffey still?

Aeneas Coffey, a former Irish excise officer, patented the two column continuous still in 1830.

What strength does a Coffey still produce?

Grain whisky from a Coffey still typically comes off at around 94% ABV. Scotch rules require distillation to less than 94.8% ABV.

Is grain whisky the same as vodka?

No. Grain whisky is distilled to a lower strength than neutral spirit and must mature in oak, so it keeps cereal and sweet character that vodka is designed to remove.

Why is most grain whisky used in blends?

Its light, soft character gives a blend body and smoothness, while the malts in the blend bring the stronger flavours.