Which of the following grains must bourbon be made from, according to legal definitions?

Bourbon is a distinct type of whiskey that must adhere to specific legal definitions established in the United States. One of the most critical requirements is that the grain mash must contain at least 51% corn. This requirement is integral to the identity of bourbon, as it contributes to its sweetness and rich flavor profile.

Corn is the primary grain used in bourbon production, differentiating it from other whiskey styles that may be based on different grains. The use of 51% corn ensures that the resulting spirit retains the characteristics that are expected of bourbon, such as its smoothness and full-bodied taste.

In contrast, the other grains mentioned, like barley, wheat, and rye, while they can be part of a bourbon mash bill, do not meet the legal requirement to qualify as bourbon on their own. Bourbon must predominantly feature corn to maintain its classification and authenticity. Thus, corn is the defining grain required by law for bourbon production.