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Under Scotch Whisky Regulations, a "Single Malt Scotch Whisky" must be made exclusively from malted barley (although the addition of E150A caramel colouring is allowed), must be distilled using pot stills at a single distillery, and must be aged for at least three years in oak casks of a capacity not exceeding 700 litres (150 imperial gallons; 180 US gallons).
While the Scotch model is usually copied internationally, these constraints may not apply to whisky marketed as "single malt" that is produced elsewhere. For example, there is no definition of the term "single" with relation to whisky in the law of the United States, and some American whiskey advertised as "single malt whisky" is produced from malted rye rather than malted barley.
