Bourbon needs to be aged in new American Oak barrels primarily because of legal requirements set forth by the U.S. government.

According to the Federal Standards of Identity for Distilled Spirits, to be classified as bourbon, the whiskey must meet certain criteria, including aging in new charred oak containers. This regulation ensures consistency in the production and flavour profile of bourbon, as the new barrels contribute specific flavours and characteristics to the whiskey during the aging process.

The use of new barrels also distinguishes bourbon from other types of whiskey, like Scotch or Irish whiskey, which often use barrels that have been previously used to age other spirits.