Beer and Wine
Alcoholic beverages can be divided into two broad categories according to whether or not there is a distillation stage following fermentation. Beer and wine fall into the non-distilled category whereas whisky, rum, brandy, gin, etc. have all been distilled. The latter are often referred to as "spirits" or "hard liquor". Simple distillation permits the removal of some of the more noxious congeners by discarding some of the first liquid to distill over (the"heads") and the last to distill over (the "tails"). The middle fraction of congener-ladenalcohol remains and is collected.
Because beer and wine do not receive any such purification treatment it is necessary to live with whatever mixture of chemicals the fermentation has produced. It would be nice if, after a fermentation had gone slightly wrong and the beer or wine were found to have an unpleasant taste, the offending congeners could be removed. Alas, science has not yet come up with a method for doing this. Which means in practice that beer- and wine-making must be carried out extremely carefully because you are stuck with whatever you've produced.Beer- and wine-making are highly skilled operations, more akin to gourmet cooking than to science, and involve many subtleties and many opportunities for error. Which explains why there is such a wide range of qualities and prices of wines and why amateurs have such difficulty in producing a really first-class product.