are critical to the taste and appearance of the final whisky. Principally two types of cask are used - Spanish sherry casks and American oak Bourbon casks.

Constructed of oak, casks used for whisky maturation come in a variety of sizes. Usually casks are second fill or third fill - first fill (new, unused wood) are seldom used. Ex-Bourbon casks made from American oak and ex-Sherry casks made from Spanish oak are often used because of the additional characteristics they give to the matured whisky.