Straight whiskey (or straight whisky), as defined in United States law, is whiskey that is distilled from a fermented (malted or unmalted) cereal grain mash to a concentration not exceeding 80% alcohol by volume (abv) and aged in new charred oak barrels for at least two years at a concentration not exceeding 62.5% at the start of the aging process.
This definition is established for production of American whiskey for consumption within the United States as per the U.S federal Standards of Identity for Distilled Spirits.
[3] Alternatively, straight can be regarded as a synonym for ordering or serving whiskey neat, without any water, ice, mixers, or other liquors.
In contrast, even the regulations governing single malt whiskey production in some countries allow the addition of caramel coloring to enhance appearance.
At alcohol concentrations exceeding this amount, most of the flavor from the original fermented mash that was used in the distillation process will be removed, resulting in a more neutral grain spirit.
In other countries, whiskey may be produced from a spirit that is much higher in alcoholic proof, which generally reduces the flavor derived from the original mash that was used in its production.