Whisky is a distilled alcoholic beverage made from fermented grain mash. Various grains are used for different varieties, including barley, corn, rye, and wheat. Whisky is typically aged in wooden casks, generally made of charred white oak. Whisky is a strictly regulated product in many countries, with different classes and types. The typical unifying characteristics of the different classes and types are the fermentation of grains, distillation, and aging in wooden barrels.