Malt whisky is whisky that is made from a fermented mash produced primarily from a malted grain. Unless otherwise specified, it is generally assumed that the primary grain is barley, although whisky is also made using malted rye. A whisky made from malted rye should therefore be called a "rye malt whisky" rather than simply a "malt whisky".
If the product is made exclusively from a single grain at a single distillery (and various other restrictions apply), it is called a single malt whisky.
The exact definition of a "malt whisky" and a "single malt whisky" and the restrictions governing its production vary according to the regulations governing the marketing of whisky in the local jurisdiction.
In the United States Code of Federal Regulations, the Standards of Identity for Distilled Spirits[1] define a "malt whisky" as a whisky produced at an alcohol by volume (abv) level not exceeding 80% from a fermented mash of not less than 51% malted barley grain and stored for aging in charred new oak containers at not less than 62.5% abv. The regulations define a "rye malt whisky" in a corresponding manner using rye grain. If such a whisky has been aged for at least two years, contains no added coloring and flavoring, and has not been blended with neutral spirits or other types of whisky, the additional adjective "straight" can be applied, as in "straight malt whisky" and "straight rye malt whisky". If the whisky is not completely "straight" but at least 51% of its content is "straight malt whisky", the word "malt" can still be used, but the product must be described as a "blend", as in "blended malt whisky" or "malt whiskey – a blend".
In Scotch whisky regulations,[2][3] malt whisky must be aged for at least three years, the use of new barrels is not required, the distillation and aging can use higher levels of alcohol by volume (which can result in a "lighter" but less flavorful whisky), and (E150A) caramel coloring can be added (but no other additives are allowed).
Canadian whisky regulations are generally more liberal,[4] allowing the addition of flavoring agents as well as caramel. There is no maximum limit on the alcohol level of the distillation or aging for Canadian whisky,[4] so the bulk of the distilled content (often more than 90 percent) may be neutral spirits or near-neutral spirits rather than "straight" whisky. Similar to the regulations for the aging of Scotch, the aging requirement for Canadian whisky is three years, and the use of new barrels is not required.