On 4 May 1964, the United States Congress recognized Bourbon Whiskey as a “distinctive product of the United States.” The Federal Standards of Identity for Distilled Spirits (27 CFR 5) state that bourbon must meet these requirements:
- Bourbon must be made of a grain mixture that is at least 51% corn.
- Bourbon must be distilled to no more than 160 (U.S.) proof (80% alcohol by volume).
- Bourbon must be aged in new, charred oak barrels.
- Bourbon may not be introduced to the barrel at higher than 125 proof (62.5% alcohol by volume).
- Bourbon which meets the above requirements and has been aged for a minimum of two years, may (but is not required to) be called Straight Bourbon.
- Bourbon aged for a period less than four years must be labeled with the duration of its aging.
- If an age is stated on the label, it must be the age of the youngest whiskey in the bottle.
- Only whiskey produced in the United States can be called bourbon.