Kentucky settlers brought with them the craft of making whiskey, substituting corn for other grain ingredients. Raw whiskey distilled from corn mash has a good deal of, shall we say, character, and some distillers decided to take the time to make a mellower product. Early Kentucky distillers used new oak casks which had been charred on the inside, aging the whiskey from two to six years before decanting into jugs for sale. This resulted in a superior product which eventually became the hard liquor of choice for Americans. We know it as "Bourbon."
