Rotgut

Fusel alcohols or fuselol, also sometimes called fusel oils in Europe, are a mixture of several alcohols (chiefly amyl alcohol) produced as a by-product of alcoholic fermentation. The word fusel is German for "bad liquor".

Whether fusel alcohol contributes or not to hangover symptoms is a matter of scientific debate. A Japanese study in 2003 concluded, "The fusel oil in whisky had no effect on the ethanol-induced emetic response" in Suncus murinus. Additionally, consumption of fusel oils with ethanol suppressed subjects' subsequent taste aversion to alcohol, which suggested subjects' hangover symptoms were lessened, according to the journal.

Fusel oil and fusel oil acetates are needed by the lacquer industry for high boiling lacquer solvents.

Excessive concentrations of some alcohols other than ethanol may cause off-flavors, sometimes described as "spicy", "hot", or "solvent-like". Some beverages, such as rum, whisky (especially Bourbon), incompletely rectified vodka (e.g. Siwucha), and traditional ales and ciders, are expected to have relatively high concentrations of non-hazardous alcohols as part of their flavor profile. However, in other beverages, such as Korn, vodka, and lagers, the presence of alcohols other than ethanol is considered a fault.

The compounds involved are chiefly:

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