The word whisky comes from uisge beatha, the Gaelic for "water of life" of “frisky water”. Irish whiskey has an "e" in it thanks to marketers a in the last century wanted to distinguish 'classier' Irish whiskey from large quantities of Scottish rotgut that was on the market. Oh, how times change. But nevertheless, Scotch is now always spelt whisky.
First of all I should point out the differences between vodka and whisky. Vodka, despite common misperceptions, is not made from potatoes, but can be distilled from anything with sugars that can ferment to produce alcohol. What makes it vodka is that it is distilled to as close as pure alcohol as possible, and is then cut with water. Most of the actual flavor of vodka is more to do with the quality of water that dilutes the spirit than the alcohol itself. Crappy water = crappy vodka.
Scotch is essentially distilled beer, but unlike vodka, but it's only distilled to a 75% alcohol content, and the final spirit contains 'impurities' that give it much of its flavor. The rest of the flavor and character comes from the aging process, or malting process in single malts, but more of that later…
As I said, Scotch whisky is, basically distilled beer from barley grain. The most sophisticated (and interesting) of the Scotch types, in terms of flavor and process, is single malt, and that’s what I’ll mostly be describing here. In single malt whisky, the barley is soaked in water for two or three days (the quality of the water is an important factor in the character of the whisky) and then the grain is spread out allowed to germinate for a week or more - this is the malting process during which many of the starches in the grain transform into a variety of sugars. This stage is time and labor intensive and is skipped in other types of whiskies, but it's this process that gives single malts much of their complexity. After the germination stage, the grain is dried, and this stage can also add to the flavor of the whisky. Traditionally single malts are dried in a kiln fueled by peat. The more smoke that's allowed to permeate the gain, the peatier whisky (e.g. malts from the island of Islay are smoked heavily and therefore very peaty). Again this significantly adds to the flavor in single malts, as opposed to other whiskies.
The grain is then ground up into grist and poured into a large barrel or mash tun to which water is added (again the type of water is important, and the chemical composition of the water source is important in the final flavor of the whisky). The sugars in the grain dissolve in the water and the sugary liquid, or wort is drained off. More water is added to the grist, and wort drawn off. The number of times this happens is variable and is distillery-specific.
The liquid is then has yeast added and fermentation starts on the wash as the liquid is now called. The wash is fermented for about 2 days, with a final alcohol content of about 7-8%.
Now comes the distilling. For single malts, a 'pot' still is used (which looks like a big copper Hershey's kiss) and the liquid is distilled in batches. This again is distinctive from other whiskies where distillation is continuous (in a so called Coffey still), a process which is faster and not so labor intensive.
The first distillation (referred to as the low wines; 20-25% alcohol) is taken off and distilled again (to become 75% alcohol). From this second distillate the first part (foreshot) and end part (feints) are returned to a batch the low wine for re-distilling, as they contain some noxious impurities. The middle cut or spirit is drawn off, and will be used for the whisky itself. The decision when to ' cut' is partly automated, but some distilleries rely on a still man who makes their decision based on experience, and partly magic.
The spirit is then placed in casks to age. The location for aging is important as it can affect the flavor - for example the salty sea air of Laphroaig distillery gives their whisky a distinct iodine/hospital smell (that's due to a high iodine concentration in aerosolized sea salt that permeate the casks).
For single malts the casks are charred oak bourbon barrels imported from the US (under US law bourbon barrels can only be used once). During the aging process the spirit reacts with the oak barrels, going from a clear to a golden color. The longer the spirit is aged, usually the deeper the color (and the mellower and less harsh the taste). For some brands, the spirit is transferred to a sherry, port, wine, or madeira cask to 'finish' (usually for two years) and again it picks up some subtle flavoring due to reactions with the wine infused cask wood.
During the aging process 40-50% of the whisky evaporates away and is lost. This is referred to as "the angel's share" (as an aside I highly recommend the Scottish movie "the Angel's Share" a fun "heist" movie, although non-Glaswegians will probably need sub-titles).
When aging is completed the whisky is bottled. Scotch has to be aged at least a three years and a day, with most Scotch being 8 years. Most single malts are aged 10 years. Sometimes whiskies of different ages are mixed together, but the age you see on the bottle will be the youngest batch in the mix. However, your bottle may be mixed with an older batch, often to give a more mellowed flavor. "Single cask" whisky is drawn from just one cask, and not mixed. The whisky is 55-57% alcohol at this stage, and so has to be cut with water again, to 40% (or 43% for export) with the signature water supply before bottling (unless it's bottled as "cask strength"). Once in the bottle, although there may be a little evaporation, there is no further aging as such - unlike wine, there is negligible oxidization in the bottle. So you might as well drink it.
Single malts can consist of multiple age batches, from multiple casks, but from only one type of whisky at a specific distillery. Blended scotches can have up to 40 different types of whisky within, from multiple distilleries, some single malt, but much of it grain whisky (see American whiskies below). But they all have to be made in Scotland under Scottish distilling laws.
For each region of Scotland, single malts have a slightly different flavor. Lowland malts are slightly citrusy, Islay malts are very peaty, Speyside malts are sweet and slightly fruity, and highland malts have vanilla and spicy tones.
My personal favourite is Glenmorangie (port or madeira wood finish). It’s also the favorite of Connor and Duncan MacLeod of the Clan Macleod, so for me there can be only one. At the moment I have 22 bottles of single malt in the house, and some high end bourbons too.
As a final note, Scotch should never be drunk with ice. That is sacrilegious. Connoisseurs will a tiny bit of water, no more than a teaspoonful, to their whisky, and this will in fact help bring out the favor of the scotch – IF, AND ONLY IF, the water is the best spring water. Adding crappy faucet/tap water to your fine Scotch is just plain dumb. You can now (from thinkgeek.com) get ‘whisky stones’ for your Scotch – pieces of granite that you can cool in your freezer, and chill your scotch without diluting on contaminating it. These are fine, although they will show down evaporation and you’ll lose some of the bouquet of the whisky. Just be careful how you wash the stones after – and do not, as a friend did, scrub them with detergent, or you’ll have forever soapy-tasting whisky.
Anyone who puts coke, or even worse, Iron-bru, in good single malt, deserves to fry (in batter) in a special layer of hell.
PS. In the US, whiskies are usually denoted by the cereal grain that the mash is largely (at least 51%) derived from, although bourbon is 51% corn (maize), whereas corn whiskey has a mash that is 80% corn. Bourbon that has been aged at least 2 (often 4) years and doesn’t have added colorings, flavorings or grain spirits, can be called straight bourbon. In addition to bourbon & corn whiskey, you will find barley, wheat and rye whiskies in the US (barley whiskies in the US may also be malted in a process similar, but not identical, to single malt Scotch too). Tennessee whiskey is essentially bourbon, but some distilleries filter the whisky through sugar maple charcoal, which is supposed to improve the flavor. Canadian whiskies are different again (mostly corn/wheat with other grains aged 3-6 years typically, and are usually blended, even if they are referred to as “rye” whisky). The one exception is Glenora (Nova Scotia) which is a pot stilled, single malt, produced in Scottish fashion, that I am extremely curious to try.