Cask strength

Cask strength (also known as barrel proof/barrel strength) is a term used by whisky (sometimes 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. The level of alcohol-by-volume (ABV) strength for a cask strength whisky or rum is typically in the range of 52–66% ABV.

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 about 40% ABV, which is the statutory minimum in some countries, including the United States. The degree of dilution significantly affects the flavor and general drinking experience of the whiskey or rum.