American whiskey labeled as one of these types, the whiskey must be distilled to no more than 80% alcohol by volume (160 U.S. proof) to ensure the flavor of the original mash is adequately retained, and the addition of coloring, caramel, or other flavoring additives is prohibited. All of these, except corn whiskey, must be aged at least briefly (although no minimum aging period is specified) in charred new oak containers. These restrictions do not exist for some similarly named products in some other countries, such as Canada. American corn whiskey does not have to be aged at all – but, if
American whiskey it is aged, it must be aged in used or uncharred oak barrels "at not more than 62.5% alcohol by volume (125 proof)". In practice, if corn whiskey is aged, it is usually aged in used bourbon barrels. Straight whiskey is whiskey that was distilled to not more than 80% alcohol by volume (160 proof) that has been aged for at least two years at a starting alcohol concentration of not more than 62.5%. It has not been blended with any other spirits, colorings, or additives. A straight whiskey that also meets one of the other above definitions is referred