Glossary
Diacetyl rest
Deliberately raising a fermentation’s temperature near its end so the yeast reabsorbs the diacetyl precursor it produced earlier.
The full record
Diacetyl rest has its own catalogue entry with the detail this page summarises — causes, thresholds, related styles and evidence.
Diacetyl rest — Raise a fermentation’s temperature near its end so the yeast reabsorbs and reduces the diacetyl it produced earlier.
Yeast produces a compound during growth that spontaneously converts to diacetyl — the butterscotch note — and healthy yeast then takes the diacetyl back up and reduces it to something flavourless. Cooling a lager too early interrupts that clean-up, which is why the rest exists.
It is a lager technique principally because lager fermentation is cold enough for the reabsorption to be slow. Warm-fermented ales usually clear diacetyl without intervention.
Related
More vocabulary
Arrested fermentation · Barrel ageing · Batch sparging · Biotransformation · Blending · Bottle conditioning · Bottom fermentation · Burtonisation · Cask conditioning · Centrifugation
See every term on the glossary index.
Last reviewed 2026-08-16.