Bourbon whiskey is a type of American whiskey, a barrel-aged distilled spirit made mostly from corn. Bourbon has to be Produced in the United States in order to be considered bourbon. It has to be made made from a mash bill (grain mixture) that is at least 51% corn, aged in new, charred oak barrels, distilled to no more than 160 (U.S.) proof (80% alcohol by volume), Entered into the barrel for aging at no more than 125 proof (62.5% alcohol by volume), bottled (like other whiskeys) at 80 proof or more (40% alcohol by volume). There are aging requirements for bourbon, such as straight bourbon, which has a minimum aging requirement of two years. In addition, any bourbon aged less than four years must include an age statement on its label.