A mash bill is a recipe that specifies the proportions of different grains used to produce a particular type of whiskey. The grains used in a mash bill can include corn, rye, wheat, barley, and oats. The proportions of each grain used will determine the flavor, aroma, and body of the whiskey.
Mash bills are important because they determine the final flavor and character of a whiskey. Different whiskeys have different mash bills, and this is one of the things that makes each whiskey unique. For example, bourbon whiskey must be made from a mash bill that is at least 51% corn. Rye whiskey, on the other hand, must be made from a mash bill that is at least 51% rye. The different grains used in a mash bill will also affect the aging process of the whiskey. Whiskeys that are made from a high-rye mash bill will age more quickly than whiskeys that are made from a low-rye mash bill.