Named for Bourbon County, Kentucky, this all-American liquor is distilled from fermented grain. Straight bourbon is distilled from a mash of at least 51 percent corn; blended bourbon must contain not less than 51 percent straight bourbon. Sour mash bourbon is made by adding a portion of the old mash to help ferment each new batch, in the same way that a portion of sourdough starter is the genesis of each new batch of sourdough bread.