Only whiskey produced in the United States can be called bourbon.[5]
Bourbon must be made from a grain mixture that is at least 51% corn.[6]
Bourbon must be aged in new, charred oak barrels.[6]
Bourbon must be distilled to no more than 160 (U.S.) proof (80% alcohol by volume).[6]
Bourbon must be entered into the barrel for aging at no more than 125 proof (62.5% alcohol by volume).[6]
Bourbon, like other whiskeys, must be bottled at 80 proof or more (40% alcohol by volume.)[7]
Bourbon has no minimum specified duration for its aging period, although it must be aged at least briefly.[8] However, the following definitions and requirements apply that relate to aging periods:
Bourbon that meets the above requirements, has been aged for a minimum of two years, and has no added coloring, flavoring, or other spirits may (but is not required to) be called Straight bourbon.[9]
Bourbon that is labeled as Straight that has been aged for a period less than four years must be labeled with the duration of its aging.[10]
Bourbon that has an age stated on its label must be labeled with the age of the youngest whiskey in the bottle (not counting the age of any added neutral grain spirits in a Bourbon that is labeled as Blended, as neutral grain spirits are not considered whiskey under the regulations and are not required to be aged at all).[11]
Bourbon that is labeled as Blended (or as ‘a blend’) may contain added coloring, flavoring, and other spirits (such as un-aged neutral grain spirits); however, at least 51% of such a product must be Straight Bourbon.[12][13]