American single malt whiskey consists of at least 51 percent grain, typically malted barley, though most distillers use 100 percent barley.
This is similar to single malt Scotch, which must use 100 percent malted barley, and different from American whiskies, which tend to require some combination of corn, rye, wheat and malted barley. It must be produced and aged entirely by one distillery. It must be aged in new charred oak barrels, just like bourbon and rye.
American rye whiskey is made from a mash of at least 51 percent rye. The other ingredients commonly used include corn and barley. It is distilled to an ABV less than 80% and is aged in charred, new oak barrels. Only rye which has been aged more than two years may be referred to as straight rye.
Tennessee whiskey and bourbon have almost identical requirements and most Tennessee whiskeys meet the criteria for bourbon.
The main difference in production is that, sometime after distillation, Tennessee whiskey must be filtered through sugar maple charcoal, which is often referred to as the “Lincoln County Process".
Though most producers filter directly after distillation, the law doesn’t specify when it must be done.