The Beer Off-Flavor Series: Diacetyl

This is part 3 in The Beer Off-Flavor Series by Drew Beechum.

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This little ketone (C4H6O2) flummoxes the beer world. In some styles, such as British/Irish session ales and classic Bohemian Pilsners, a low level of diacetyl can be desired, lending richness and mouthfeel.

In the United States and Germany, however, diacetyl is almost universally considered a flaw that should be avoided at all costs.

Key Indicators

The following characteristics are common when diacetyl is detected in beer:

Butter, butterscotch Movie theater popcorn Slick mouthfeel

Causes & Prevention

Poor Yeast Health

Diacetyl, like acetaldehyde, is a byproduct of fermentation. During the same process that converts …

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