Diacetyl
Term from the Brauwerkstatt brewing glossary, category “Faults and hygiene”.
Explanation
Off-flavour of butter or butterscotch, often with a slick mouthfeel. Yeast produces it in every fermentation and reabsorbs it afterwards if given enough time and some warmth. So do not end fermentation too early; for lagers a diacetyl rest helps.
Test your knowledge
What does the beer fault diacetyl taste like?
- Butter
- Clove
- Green apple
Show answer
Correct: Butter. Yeast produces diacetyl in every fermentation and reabsorbs it if given enough time and some warmth.
What do you do during a diacetyl rest?
- Add more hops
- Freeze the beer
- Raise the temperature towards the end of fermentation so the yeast reabsorbs diacetyl
Show answer
Correct: Raise the temperature towards the end of fermentation so the yeast reabsorbs diacetyl. Especially with lagers, the beer is kept warmer for a few days at the end, at about 16–18 °C (61–64 °F).