Scotch whisky must mature in oak casks for at least three years.
This requirement is set by the Scotch Whisky Regulations 2009, which define how Scotch may be produced, labelled and sold. The spirit must also be made in Scotland from water and malted barley, with other whole cereal grains permitted for some categories, and it must be fermented, distilled and matured in Scotland.
The three-year minimum applies to both single malt and blended Scotch. Many whiskies are matured much longer, including 10-, 12- and 18-year expressions, but the age statement refers to the youngest whisky in the bottle. A whisky labelled “12 years old” may contain older spirit, but none younger than 12 years.
Maturation takes place in oak casks, often previously used for bourbon, sherry or other wines. The cask influences colour, aroma and flavour while some liquid evaporates as the “angel’s share.”