Bourbon is a style of corn-based, barrel-aged whiskey that originated in the southern United States, most notably in the state of Kentucky. Under U.S. law, the definition of Bourbon whiskey is "whiskey produced at not exceeding 160° proof from a fermented mash of not less than 51% corn and stored at not more than 125° proof in charred new oak containers." The mash bill can also include other grains, such as rye, barley and wheat.