In Scotland, Maltwhisky is always made using 100% malted barley. In the U.S. many malt whiskeys (especially those labeled “single malt”) are made with 100% malted barley as well. But they don’t have to be: U.S. regulations stipulate that malt whiskey is only required to have a minimum of 51% malted barley in the mashbill.
Like bourbon and rye, the maximum proofs for distillation and barrel entry for American malt whiskey are 160 and 125, respectively. Additionally, it must be stored in new, charred oak barrels. Therefore, American malt whiskeys are closer kissing cousins to bourbon and American rye...
