Mixture of higher alcohols formed as a by-product of carbohydrate fermentation in the production of ethyl alcohol. Flavor constituent of beer, wines and distilled spirits. Varies widely in composition, depending on the fermentation raw material used, but contains chiefly isopentyl alcohol and 2-methyl-1-butanol as well as isobutyl alcohol (20%), n-propyl alcohol (3-5%), and small amounts of other alcohols, esters and aldehydes. Composition of grape brandy fusel oil: A. D. Webb et al., Anal. Chem. 24, 1944 (1952). HPLC determn of constituents: M. E. Neale, J. Chromatogr. 447, 443 (1988). Review: A. G. Patil et al., Int. Sugar J. 104, 51-58 (2002).