Fusel Oils: A Look at Fermentation By-Products

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July 18, 2014 by Prost Brewing

Fermentation by-products like fusel oils may contribute to aroma and taste.

Fermentation by-products like fusel oils may contribute to aroma and taste.

We recently told you about esters in bier, which are flavor compounds created as a result of fermentation. There are other by-products created during fermentation that sometimes affect the way the bier tastes, and possibly the way it makes you feel. During fermentation, yeast converts sugars in the wort into alcohol and carbon dioxide, as well as heat and other by-products that can determine flavor and aroma. Higher alcohol levels are a portion of the by-products.

A portion of the higher alcohols are known as fusel oils. For certain bier styles, higher amounts of fusel oils are unwanted, as they may add a sharp alcohol or solvent flavor to the bier. Fusel is a German term that means “bad liquor.” On their own, fusel oils usually fall under the threshold for taste and aroma. When combined with other fermentation by-products called congeners, fusel oils may be present in the bier’s aroma and taste. It’s been said that these by-products also contribute to headaches and hangovers.

At Prost Brewing, our brewers work hard to produce the appropriate amount of such by-products during fermentation. One major way to do this is to maintain firm control of fermentation temperature. Fermentation is a science within itself, and it takes a thorough understanding to produce the most excellent German style bier.


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