Whisky or whiskey is a type of distilled alcoholic beverage made from fermented grain mash. Different grains are used for different varieties, including barley, malted barley, rye, malted rye, wheat, and corn. Whisky is typically aged in wooden casks, made generally of charred white oak.
Whiskey is a strictly regulated spirit worldwide with many classes and types. The typical unifying characteristics of the different classes and types are the fermentation of grains, distillation, and aging in wooden barrels.
TYPES OF WHISKEY
Malt whiskey: is made primarily from malted barley.
Grain whiskey: is made from any type of grains.
Malt and grain are combined in various ways
Single malt:is whisky from a single distillery made from a mash that uses only one particular malted grain. Unless the whisky is described as “single-cask”, though, it will contain whisky from many casks, and different years, so the blender can achieve a taste recognisable as typical of the distillery. In most cases, the name of a single malt will be that of the distillery with an age statement and perhaps some indication of some special treatments such as maturation in a port wine cask.
Blended malt whiskey:is a mixture of single malt whiskies from different distilleries. If a whisky is labelled “pure malt” or just “malt” it is almost certain to be a blended malt whisky. This was formerly called a “vatted malt” whisky.
Blended whiskeys:are typically made from a mixture of malt and grain whiskys — often along with neutral spirits, caramel, and flavouring. A whisky simply described as a Scotch, Irish, or Canadian whiskey is most likely to be a blend. A blend typically contains whisky from many distilleries so that the blender can produce a flavour consistent with the brand, and the brand name (e.g., Chivas Regal, Canadian Club) will usually not therefore contain the name of a distillery.There are exceptions.
Cask strength:(also known as barrel-proof) whiskies are rare, and usually only the very best whiskies are bottled in this way. They are bottled from the cask undiluted or only lightly diluted.
Single cask:(also known as single-barrel) whiskies are usually bottled by specialist independent bottlers, such as Duncan Taylor ,Gordon & MacPhail, and Kentucky Bourbon Distillers , amongst others. Each bottle of a single-barrel whisky is from an individual cask, and often the bottles are labelled with specific barrel and bottle numbers. The taste of these whiskies may vary substantially from cask to cask within a brand.
Whiskys do not mature in the bottle, only in the cask, so the “age” of a whisky is only the time between distillation and bottling. This reflects how much the cask has interacted with the whisky, changing its chemical makeup and taste. Whiskies that have been bottled for many years may have a rarity value, but are not “older” and will not necessarily be “better” than a more recently made whisky matured in wood for a similar time. After a decade or two, additional aging in a barrel will also not necessarily make a whisky “better”.
Most whiskies are sold at or near an alcoholic strength of 40% abv, which is the statutory minimum in some countries – although the strength can vary, and cask-strength whisky may have as much as twice that alcohol percentage.
The first record of whiskey ever to have appeared is In the Irish Annals of Clonmacnois in 1405. the first written record of whisky appears describing the death of a chieftain at Christmas from “taking a surfeit of aqua vitae”.In Scotland, the first evidence of whisky production comes from an entry in the Exchequer Rolls for 1494 where malt is sent “To Friar John Cor, by order of the king, to make aquavitae”, enough to make about 500 bottles.
At that time ,whiskey did not taste at all like how it tastes today, because it was aged much less probably a more crude taste. through trial and error and thanks to the bravery of those individuals who drank from the casks that were forgotten at the back of the warehouse, the whiskey became smoother and started resembling that fine drink ,we drink today.
The idea to make whiskey at first occurred in Ireland where grapes(for wine) were less common and so they started to distill barley, then the idea traveled to Scotland then England the rest of the world
This is really a nutshell much more about the full history of distillation and the discovery of whiskey can be found on the wiki page.