Single malt whisky (and sometimes a third) time. The final spirit, called "new make spirit", generally has an alcohol content of 60 to 70%. Most new-make malt whisky is diluted to about 62.5% a.b.v. before it is placed in casks to mature. The "new-make spirit", or unaged whisky, is then placed in oak casks to mature. By law, all Scotch whisky must be aged for a minimum of three years in oak casks, though many single malts are matured for much longer. The whisky continues to develop and change as it spends time in the wood, and maturation periods of twenty years or
Bourbon whiskey oak containers for aging. In practice, these containers are generally barrels made from American white oak. The spirit gains its color and much of its flavor from the caramelized sugars and vanillins in the charred wood. Straight bourbon must be aged at least two years, and blended bourbon must contain at least 51% straight bourbon on a proof gallon basis (i.e., most of the alcohol in the blend must be from straight bourbon). The remainder of the spirits in a blended bourbon may be neutral grain spirits that are not aged at all. If a product is labeled merely as