What must Kentucky Bourbon be aged in?

Kentucky Bourbon must be aged in new, charred oak containers. This requirement is crucial because the interaction between the bourbon and the wood of the barrel significantly influences the spirit's flavor, aroma, and color. The charring process creates a layer of caramelization inside the barrel, which imparts rich flavors such as vanilla, caramel, and other complex notes to the bourbon as it ages.

Using new barrels is an essential criterion for bourbon, as it ensures that the whiskey has access to the full range of flavors from the fresh oak, instead of the diminished contributions that would result from using previously used barrels. This is a defining characteristic of bourbon production and separates it from other types of whiskey, which may have different aging requirements.