A bourbon grain bill is a recipe that specifies the proportions of different grains used to make bourbon whiskey. The most common grains used in bourbon are corn, rye, wheat, and barley. Corn is the primary grain, and it must make up at least 51% of the mash bill. Rye, wheat, and barley are used in smaller proportions to add flavor and complexity to the whiskey.
The grain bill is an important factor in determining the flavor of bourbon. Different grains impart different flavors and aromas to the whiskey. For example, corn gives bourbon its sweetness, while rye adds spice and pepperiness. Wheat and barley add smoothness and body to the whiskey.