fusel oil is a category of organic compounds that are byproducts of alcoholic fermentation. These include secondary alcohols like methanol, propanol, and amyl alcohol as well as higher alcohols that have boiling points higher than ethanol. When present in small amounts they provide flavor to spirits like rum, brandy, and whisky. In excess, they can have a negative impact, producing a hot, solvent-like flavor. Fusel oils are known to have adverse health effects that lead to more severe hangovers. The more volatile compounds in fusel oil tend to dissipate during barrel aging, but many remain in the spirit.
See also methanol and ethanol.
Herstein, Karl M., and Morris Jacobs. Chemistry and Technology of Wines and Liquors. New York: D. Van Nostrand, 1948.
By: Darcy O’Neill