While Malt Whisky can only be made from barley, Grain Whisky is made from a mixture of grains, typically wheat and maize (corn) and it may also contain barley.
Grain whisky is distilled in a continuous column still, also known as Coffey still. Coffey still distillation is generally accepted to yield lighter and less complex flavour than pot still distillation (distinctive to malt whisky).
In Scotland, pure Grain Whisky is seldom bottled, it is typically used in the production of blended whiskies that combine grain and malt whiskies. Occasionally well-aged grain whiskies are released as "single grain whisky".
Scotland is the home to 6 grain distilleries: Cameronbridge, Girvan, Invergordon, North British, Port Dundas and Strathclyde. Together they annually produce six times the amount of malt whisky. Only three of the aforementioned distilleries bottled their own single grain whiskies: Cameron Bridge, Black Barrel (from Girvan) and Invergordon.