An enzyme which hydrolyzes starch to produce dextrins, maltose, and glucose. When grain seeds are sprouted, the grain produces amylase to convert the starch in the grain into sugars which the grain needs for growth. This ability to convert starch into sugars is why people who make beer or whiskey from grains use malt, which is barley that has been sprouted and then dried to arrest the amylase in the grain.
There are several different forms of amylase: α-amylases act at random locations along the starch chain to break down long-chain carbohydrates into shorter chains (that are still too big for yeast to digest). β-amylase, instead of acting in the middle of the chain, acts at one end of a carbohydrate chain, cleaving off two glucose units at a time. This smaller, two-unit carbohydrate is called maltose, and is directly usable by the yeast. These two types of amylase act as a 'tag-team', with α-amylase creating a bunch of exposed ends, and β-amylase chewing each exposed end to make fermentable sugars.