Grain whisky definition
In Scotland, "malt whisky" must use a 100% malted barley mash and must be distilled in a pot still, whereas grain whisky is typically distilled in a continuous column still in a manner that results in a higher percentage of alcohol by volume (ABV), but less flavorful spirit. Because of this practice, grain whisky is seldom bottled by itself in Scotland, where it is instead manufactured primarily for blending with malt whisky to create blended whiskies, which account for over 90% of all Scotch whisky sales. The comparative lightness of the clearer, more-neutral-flavored grain whisky is used to smooth out the often harsh characteristics of single malts. Occasionally well-aged grain whiskies are released as single grain whisky if made at one distillery or blended grain whisky if combining spirits from multiple distilleries.
Also outside of Scotland, the use of continuous column stills and the use of a non-barley mash is not so closely associated with the production of "light" whisky (whisky with little flavor due to distillation at a very high ABV). For example, nearly all American whiskey is produced using column stills, and all American whiskey that is labeled as straight whiskey (including straight Bourbon and straight rye) is required to use a distillation level not exceeding 80% ABV. Because of this constraint, much of the American whiskey may actually be less "light" than some Scotch or Irish single malt pot still products. In the United States whiskey produced at greater than 80% abv is formally classified as Light whiskey and cannot be labeled with the name of a grain or called malt, bourbon or straight.