ABV, Proof and Cask Strength

The strength printed on a label shapes how a whisky smells and tastes as much as its age or cask.

ABV

Alcohol by volume is the percentage of the liquid that is pure alcohol. A 70cl bottle at 40% ABV holds 28cl of pure alcohol. Scotch, and whisky across the EU and US, must be bottled at at least 40% ABV.

Proof

• US proof is simply double the ABV: 100 proof = 50% ABV.
• The old British proof system is different: 100° proof was about 57.1% ABV. Legend says it came from testing whether spirit-soaked gunpowder would still ignite — "proof" that it hadn't been watered down. British proof hasn't been used on labels since 1980, but you'll see it on old bottles.

Cask strength

Most whisky is reduced with water to a standard strength before bottling. Cask strength (or "barrel proof" in America) is bottled as it came from the cask, without dilution — usually somewhere between 50% and 65% ABV. It gives you the full intensity and lets you choose how much water to add.

Why so many whiskies are 46%

Below roughly 46% ABV, some fatty acids and esters can drop out of solution when cold, making whisky hazy. Chill filtration — cooling the whisky and filtering it — prevents this, but some drinkers feel it strips texture. Many distilleries that don't chill-filter bottle at 46% or above, where haze is much less of a problem.

How strength changes flavour

Alcohol carries aroma, so higher strength means more intensity — but it also numbs the nose and tongue. That's why a few drops of water can make a strong whisky taste more flavourful, not less. See Water, ice and why they matter.