Whether it is whisky or whiskey has been the basis of many arguments over many years. The Scots spell it whisky and the Irish spell it whiskey, with an extra ‘e’. This difference in the spelling comes from the translations of the word from the Scottish and Irish Gaelic forms.
Whiskey with the extra ‘e’ is also used when referring to American whiskies. This ‘e’ was taken to the United States by the Irish immigrants in the 1700s and has been used ever since. Scotland, Ireland and America all have a rich heritage in the whisky industry.
It is the distillation process that one of the main differences occurs. Generally, Scottish and American whiskies are distilled twice and Irish whiskey is distilled three times (there are exceptions to the rule, in all cases). Distilling three times produces a lighter and smoother spirit.
For a whiskey to qualify as bourbon, the law–by international agreement–stipulates that it must be made in the USA. It must be made from at least 51% and no more than 79% Indian corn, and aged for at least two years. (Most bourbon is aged for four years or more.) The barrels for aging can be made of any kind of new oak, charred on the inside. Nowadays all distillers use American White Oak, because it is porous enough to help the bourbon age well, but not so porous that it will allow barrels to leak. It must be distilled at no more than 160 proof (80% alcohol by volume). Nothing can be added at bottling to enhance flavor or sweetness or alter color.
The other grains used to make bourbon, though not stipulated by law, are malted barley and either rye or wheat. Some Kentucky bourbon makers claim that the same limestone spring water that makes thoroughbred horses’ bones strong gives bourbon whiskey its distinctive flavor.