Grains don't ferment until they're malted or partially sprouted. Natural enzymes in the grain -- barley, for Scotch whisky -- begin breaking down its starches into sugars, which yeasts can feed on. Brewers and distillers toast the barley malt to stop this process when the sugars are at a peak. Scottish distillers toast their barley over a peat fire, giving it a distinctively smoky flavor. Whisky begins with a watery, beer-like slurry of this toasted barley malt and yeast, referred to as the "wort". It's distilled in either modern columnar stills or traditional pot stills, which concentrate the alcohol. It is then aged in wooden casks to mellow the raw spirits and create new flavors.

It's this aging in oak barrels that creates much of the subtlety in a Scotch whisky. The wood is porous and allows the spirit to gently oxidize over time and the evaporation slowly reduces the quantity of whisky in the barrel and concentrates its flavors. The charred barrels give the spirit its mellow amber color -- some distillers add caramel color as well -- and adds a variety of caramel and vanilla notes to the finished whisky. Some distillers purchase used barrels from makers of wine and other spirits and transfer the whisky to these barrels late in its aging process. That "finishing" process lends a hint of the original beverage's flavor to the whisky.

Blended Scotch creates a consistent, identifiable flavor profile by combining a number of these malt whiskies with neutral-flavored grain alcohol. This ensures that aficionados of a specific brand can expect the same flavors, year after year. Each brand has its own combination of smoky, sweet, salty, floral, fruity and caramel or butterscotch flavors, which its adherents can recognize immediately. The age given on the bottle's label refers to the youngest whiskies used in the blend. Blends made with older whisky tend to have more subtlety and finesse, but still adhere to the brand's distinctive flavor profile.

Many vocal but uninformed single-malt enthusiasts don't realize that their own favorite is also blended. Aside from a few specialty whiskies, known as single-cask bottlings, distillers blend their single-malt offerings from multiple casks of the same whisky at different ages. This minimizes any differences in the whisky's distinctive character from one year to the next, ensuring a consistent product. Single-malt Scotch contains no neutral grain alcohol. Although blended Scotches capture the same flavors as single malts, a good single malt expresses those flavors with considerably more delicacy and subtlety. Malt whiskies from the Lowlands, Highlands, Speyside and the Islands all have distinctively different characteristics.

Because each single malt is a product of a single distillery and a consistent process, it shows the differences between distilleries more clearly than a blended Scotch does. Lowland whiskies are light and approachable, while Island whiskies generally are the heaviest and peatiest. Speyside malts are cherished for their honeyed, sweet and fruity notes, while Highland whiskies are usually drier and more austere. Within those broad categories, the flavors of each whisky are determined by factors such as the quality of its water and choices made during the whisky's production. The strain of barley, how long it's malted, how darkly it's roasted and how much peat is used can all affect its final flavor.