Cask strength

Cask strength (also known as barrel proof/barrel strength) is a term used by whisky (spelt "whiskey" in Ireland and the United States) and rum producers to describe a whisky or rum that has not been substantially diluted after its storage in a cask for maturation.

[1] Most bottled whisky and rum is diluted with water to reduce its strength (i.e., ABV level) to a level that makes it less expensive to produce and more palatable to most consumers – usually 40% ABV, which is the legal minimum to still be classified as whisky/rum in most countries, including the United States, United Kingdom, and all EU member states (although this can be as low as 37% in Australia[2] or as high as 43% in South Africa[3]).

The degree of dilution significantly affects the flavour and general drinking experience of the whisky or rum.

Storage conditions in Kentucky and Tennessee, where nearly all of it is produced, allow the proof levels to rise during aging.

[7] The flavour profile and "heat" – the burning sensation caused by ethanol – of a given whisky change as it is diluted, and cask strength whiskies allow consumers control over this dilution process, allowing them to add water or ice according to their tastes.