While bourbon, by law, must be corn-based, other grains like barley, wheat, and rye are often added to speed up fermentation or create a specific flavor profile. The recipe that determines the proportions of these grains is called the "mash bill," and high-wheat mash bills versus high-rye produce quite different bourbons.

The high-wheat bourbon category includes popular brands like Maker's Mark, which has a mash bill of 70% corn and 16% red winter wheat, with the remainder made up of malted barley. The purpose of wheat is to impart sweeter, more mellow flavors, and vanilla and caramel are the most commonly-cited flavor notes.

High-rye bourbons tend to contain even more rye than high-wheat varieties contain wheat, and are famed for their spicy complexity and peppery finish. While Woodford Reserve is perhaps the most famous high-rye bourbon, Redemption might be the most rye-centric of high-rye producers, as it balances its 60% corn with 38.2% rye.