Bourbon, by law, must be distilled from 51 percent corn and no more than 49 percent other grains and water. Bourbon makers may add wheat, rye, barley, malt and yeast to the corn mash. No other additives are allowed in bourbon, except for water to reduce the alcohol content.
Laws also require bourbon to be between 80 and 160 proof and to be aged in new charred oak barrels. No legal minimum aging time exists for bourbon, unless it is straight bourbon; straight bourbon must be aged at least of two years and have a label with the length of its aging time if that time is less than four years.