fusel oil (fyōˈzəl) [key], oily, colorless liquid with a disagreeable odor and taste. It is a mixture of alcohols (largely amyl alcohols) and fatty acids, formed during the alcoholic fermentation of organic materials. After imperfect distillation of these fermentation products it becomes an impurity in the distilled liquor. Fusel oil is used as a solvent in the manufacture of certain lacquers and enamels (it dissolves nitrocellulose). It has a detrimental effect on the human system.