Like whiskey and other spirits, Sherry is aged in wooden barrels or casks. Distilleries began the tradition hundreds of years ago using those casks to finish their Scotch or other spirits. The residue of Sherry in the wood impartes sweet, fruity notes and helped soften the flavor.

Sherry casks now come at a premium price, spawning an industry of companies who make seasoned sherry-soaked casks specifically for use in the finishing process.