Single-cask whiskey and single-barrel whiskey are interchangeable terms to describe a whiskey that has been bottled after aging in a single barrel rather than being blended from multiple batches. Whiskey producers often blend many batches of grain and malt whiskeys to produce a particular desired flavor. Only premium whiskey is bottled from a single barrel.

Whiskey is made in five basic steps: malting or preparing the grain, mashing, fermenting, distilling and aging. First, the grain -- be it wheat, corn or rye -- is ground and cooked and the barley is malted. This means it is wet and allowed to sprout. The cooked grain and malted barley are mixed with warm water in the mashing process. (All whiskeys contain barley, but Scotch whisky -- note the different spelling -- is made with barley only.) Yeast is added, and the mixture ferments and becomes alcoholic. Then it is distilled to concentrate the liquid and increase the alcohol content. Finally, it is poured into barrels to mature.

Whiskey aging barrels, or casks, are typically made of charred white oak. In the United States, each barrel is usually used only once; in Europe, the aging process is done only in old barrels that have been used to make sherry or previous batches of whiskey. The whiskey must age at least three or four years before it is mature, although it is often aged as many as 15 years. Up to 2 percent of the volume is lost each year to evaporation; this is known as the "angels' share."

The time spent in the barrel allows the whiskey to mellow and become more smooth, although it is not known exactly how the process works. It is known that the wood of the cask allows the whiskey to "breathe" while imparting its own flavors to the liquid. The single-use wood of American barrels imparts more flavor than the older barrels used in the United Kingdom and elsewhere, which accounts for some of the flavor differences between American and European whiskeys.

Single-barrel whiskeys, often Scotches known as single malt, are prized for their purity and distinctiveness, while the vast majority of whiskeys are blended from multiple batches. Blending strongly flavored and more subtly flavored batches of whiskey is thought to produce the best flavor possible. Of course, the superiority of single-barrel or blended whiskey is simply a matter of personal preference.