Whisky, Brandy, Rum
The distiller of these products uses a simple pot still or a pot still slightly modified to give a small amount of reflux (see next section). Such stills effect only a crude separation of the fermented liquor into heads, tails and a middle fraction. The skill in making a palatable whisky consists of a) fermenting the mash under a carefully controlled set of conditions to generate a particular mixture of organic compounds, followed by b) distilling the mixture and discarding a portion of the heads and a portion of the tails. For example,you wouldn't wish to drink the acetone and methanol which arrive first but you might wish to retain some of the congeners which arrive immediately afterwards. The middle fraction,consisting chiefly of ethanol, will also contain the retained portion of heads and tails. It is these heads and tails which impart the characteristic flavour and aroma of each batch, and since the amount retained is controllable, the flavour of the final whiskey is affected accordingly. At this point there is no colour and the fiery liquid will look like water.
Colour is imparted by storing the spirit in oak barrels for a number of years, a process which also modifies to some extent the chemical make-up of the whisky to give the unique characteristics of a particular brand. If insufficient colour is imparted to the whisky by the barrel used for aging, a little caramel is added by the manufacturer.
Clearly, the manufacture of a palatable whisky is a highly skilled operation which has taken years of trial-and-error, taste panels, and feedback from consumers to reach the point where it is today. It has involved the production of a complex but controlled mixture of compounds followed by the selective removal of a certain proportion of them. This Makes it easy to understand why the moonshine produced in the hills of Kentucky during prohibition days was such a rough and even dangerous product. The fermentation carried out under less than ideal conditions would have produced a witches brew of chemicals while the crude pot stills used without proper controls would undoubtedly have left behind a number of exceedingly unpleasant constituents. Additionally, in order to increase the quantity of saleable product the moonshiners would have been strongly tempted to retain an excessive amount of the more noxious heads and tails, or even to add some cheap adulterant such as rubbing alcohol or gas-line antifreeze.
Similar problems, though less extreme of course, would face the amateur whisky maker today, so we highly recommend that you serve your distilling apprenticeship making vodka. It is the simplest of all distilled spirits to make and the safest. Then graduate to the far more challenging task of distilling a palatable whisky.