In the fermentation of the mash of cereals, the starch of which has been converted into sugar by malt, there is formed not only ethyl alcohol in great abundance, but also small quantities of other associated alcohols. Among these the chief are butyl, propyl and amyl alcohol. The latter is the most abundant of these three. There are doubtless traces of other alcohols, and they are important even though present in minute quantity.

These alcohols together form the oily constituent which is characteristic of whisky, especially of old whisky, and they have collectively been called "fusel oil." This is rather an unfortunate term, because it is associated with the bad taste and bad odor of the commercial article known under that name. The bad taste and the bad odor of the article known to commerce as fusel oil are not due to anyone of the three alcohols mentioned, but to certain other volatile bodies mostly formed during fermentation.

The case is very much the same as that of wood alcohol, chemically known as methyl alcohol. Crude wood alcohol has such an excessively repugnant and nauseating taste and odor that it is employed in many countries for denaturing ethyl alcohol and making it unfit for consumption. The bad taste and odor of wood alcohol are not due to the methyl alcohol, which it contains, but to the impurities which are generated during the manufacture of the product.

When wood alcohol is purified and refined, so as to become a chemical unit, it is not unpleasant to the taste nor to the nostrils. Such a product is called Columbian Spirits.

Quantity Of Fusel Oil

The quantity of fusel oil in a whisky is not very large, but this is the principal component of the whisky aside from the ethyl alcohol and the water. The average quantity of fusel oil in a whisky may be stated as 25/100 of 1 percent for alcohol of 100 proof; that is, 50 percent of alcohol by volume.