What type of barrel is primarily used for aging bourbon?

Bourbon must be aged in new charred oak barrels, which is a requirement outlined in U.S. law. The use of new barrels is significant because the fresh oak contributes distinct flavors and characteristics to the spirit, such as vanilla, caramel, and spice, due to the compounds extracted from the wood during aging. The charring process creates a layer of carbon that further enhances the flavor profile by providing additional notes and a smoother finish as the bourbon interacts with both the charred wood and the air within the barrel over time.

The other choices do not align with the legal parameters for bourbon production. Used oak barrels are typically associated with aging spirits like Scotch whisky or certain other types of whiskey where the previous contents have an influence. Stainless steel barrels are used for fermentation and storage but do not impart any flavor, making them unsuitable for aging bourbon. Neutral barrels, which are usually used to age spirits that require minimal interaction with the wood (like some vodkas or light rums), would also fail to provide the necessary flavor profile that bourbon requires. Thus, the only correct option for the aging of bourbon is new charred oak barrels.