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I'd recently heard of fusel alcohol in a reference that it causes headaches/hangovers. First what is fusel alcohol, and what creates it (can I avoid it)? Secondly, is fusel alcohol really the main culprit behind hangovers? I know I stopped making/drinking mead as it was a guaranteed hangover for me the next day.

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up vote 7 down vote accepted

Fusel alcohols refer to alcohols that contain more than two carbons. Ethanol (the good stuff) is a two carbon atom molecule. They happen naturally during all fermentations, with higher concentrations occurring when the yeast are under stress (including high temps). Keep in mind stress is a relative term biochemically speaking.

Fusels contribute to the severity of a hangover for certain. However, hangovers are mostly still a function of dehydrated after consuming ethanol alone. The fusels just amplify the effect. Consuming too much pure ethanol will still give you a hangover, if ones hydration isn't taken care of too.

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Can you add sources for the hangover claim? – markus Jun 28 '15 at 17:11

Fusel Alcohol

I think it's generally accepted that fusels are produced when fermentation temperature is not properly controlled, or nutrients are not at the proper concentration. Essentially, stressed yeast produce fusel alcohols. Apparently, most people believe that fusels promote headaches, but it's not scientifically proven.

In general, fermentation conditions that promote cell growth, such as temperature, aeration, and nitrogen, result in higher levels of fusel alcohols.

--Yeast, The Practical Guide to Beer Fermentation: White & Zainasheff, pp36-37

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+1 for a good answer, but molecular answer wins – BozoJoe Dec 9 '10 at 17:48

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