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Ask the Experts: Addressing Buttery Flavor in Beer

Homebrew expert Brad Smith, author of the Beersmith homebrewing software and the voice behind the Beersmith podcast, talks about buttery flavor in beer and how to prevent it from happening.

Brad Smith Dec 31, 2018 - 3 min read

Ask the Experts: Addressing Buttery Flavor in Beer Primary Image

A Craft Beer & Brewing Magazine reader recently asked us the following question:

Why do some of my beers have a buttery flavor to them?

That buttery flavor is an off-flavor usually caused by fermentation problems. It is created by a compound called diacetyl, which is a by-product of fermentation. Diacetyl can produce a flavor like buttered popcorn or a slightly butterscotch flavoring. Diacetyl is one of two major vicinal diketones (VDKs) produced during fermentation. The other is pentanedione, which has a honey flavor to it. Both are present in all beers, although usually they are well below the threshold where they can be detected. Lighter ales and lagers are more susceptible to diacetyl problems simply because the compound is easier to detect in a light-flavored beer.

Diacetyl is produced during active fermentation, but yeast can actually mop up diacetyl during the later phases of fermentation. To aid yeast in cleaning up diacetyl, it is important that you do a diacetyl rest, which involves raising the temperature of the finished beer by a few degrees at the end of fermentation. This can be done with both ales and lagers, and a healthy yeast population can clean up diacetyl in as little as a few hours, although usually the diacetyl rest is maintained for a day or two.

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