Rye Whiskey is defined under United States law as a distilled spirit made from a mash of at least 51% rye grains. During distillation, it must not exceed 160 U. S. proof. After being distilled, it is aged in charred, new oak barrels. Historically, rye dominated whiskey production in the northeastern states, Maryland and Pennsylvania in particular. At the time of his death, George Washington operated the largest rye whiskey distillery in the country at Mount Vernon.