Scotch whiskey is a particular type of whiskey made in Scotland, which is generally just called Scotch. There are five main varieties of whiskey, with single malt Scotch, vatted malt Scotch, blended Scotch, single grain scotch, and blended grain Scotch. Scotch dates back to at least the late-15th century, although it likely existed for decades before. For hundreds of years, excessive taxation led to only a handful of licensed distilleries, but since the early-19th century there have been a wide range of distilleries, all producing their own take on single malt Scotch.
One can separate Scotch into two main categories: blended or single Scotches. Not all Scotch is made from malted barley, and the majority of Scotch uses different sorts of grain. Blended grain whiskey, for example, uses different grain whiskeys from different distilleries, mixing them to get the desired flavor. Single grain Scotch doesn’t necessarily only use malted barley, or even all barley, but it does all come from a single distillery. Vatted Scotch takes a number of distilleries’ single malt Scotch offerings and blends them together. And blended Scotch whiskey combines single malt Scotch with grain whiskey, from different distilleries.
Single malt Scotch, however, is generally looked on as the finest type of Scotch. It must be distilled by a single distillery, made only with malted barley, in Scotland, using a pot still. Additionally, a single malt Scotch must be aged in Scotland, in oak casks, for at least three years, although most single malts are aged for substantially longer before bottling. Because of the relatively-small sizes produced in single malt Scotch, as well as the high level of controls enforced, it tends to be relatively expensive, and the highest-end single malt Scotches can be extremely costly.
The production of single malt Scotch relies on fairly small batches being produced, to ensure a high level of quality. These batches are then tasted and blended at the distillery to create the proper blend and final single malt Scotch. Larger distilleries generally have more consistency from year to year, as they have large numbers of batches to blend to achieve such consistency, while smaller distilleries may experience more deviation from a norm. Some distilleries actually pursue deviation in their Scotch, allowing the batches from a given year to determine that particular vintage, much in the way wine works.
There are only three ingredients in single malt Scotch, and so each of these ingredients is treated with the utmost care. While other Scotches may use other grains, single malt Scotch relies exclusively on barley, yeast, and water in its preparation. Water may come from different sources, with many modern distilleries using distilled water to better control their flavor, while most traditional distilleries use a local source of spring water that is treated as a source of pride. The barley is allowed to germinate for a few days in this water, providing the malt for the Scotch by converting the barley starch into sugars that can ferment into alcohol. Peat smoke is often also added to the process, to give the Scotch a distinctive smoky flavor.