All bourbon is corn-fueled. By nature, bourbon must have at least 51 percent corn in its base (or mash bill) with a supporting cast of malted barley, rye, and/or wheat, generally. The vast, vast majority of bourbon on the shelf will have a mash bill with around 70 to 79 percent corn in its mash. High-rye bourbons will drill that corn number down to 51 to 69 percent (as will high-wheat bourbons), whereas with low-rye or low-wheat bourbons the corn component will reach 80 percent and above.