Fusel or Fousel Oil

Fusel or Fousel Oil, known also as POTATO SPIRIT, is a frequent impurity in spirits distilled from fermented potatoes, barley, rye, &c., to which it communicates a peculiar and offensive odour and taste, and an unwholesome property. Being less volatile than either alcohol or water, it accumulates in the last portions of the distilled liquor. It is principally formed in the fermentation of alkaline or neutral liquids, but does not occur in acidulous fermenting fluids which contain tartaric, racemic, or citric acid. It mainly consists of a substance to which chemists have given the name of amylic alcohol, whose composition is represented by the formula $C\_5H\_\{12\}O$. It is a colourless limpid fluid, which has a persistent and oppressive odour and a burning taste. It is only sparingly soluble in water, but may be mixed with alcohol, ether, and the essential oils in all proportions. Any whisky which produces a milky appearance, when mixed with four or five times its volume of water, may be suspected to contain it. Fusel oil is used for making pear-essence (amylic acetate—for the so-called 'pear-drops'), essential oils, and patent varnishes, and as a solvent for barks. See ALCOHOL, WHISKY.