Scotch whisky is made primarily from malted barley. By law, Scotch whisky must be produced in Scotland and aged in oak barrels for at least three years. While other grains can be used in grain whiskies (for blends), malted barley is the primary and defining ingredient for single malt Scotch whisky. Oats are used in brewing, maize (corn) in American whiskey, and wheat in some blended whiskies.