Glossary
Open fermentation
Fermenting in a vessel open to the air rather than in a sealed tank, allowing krausen to be skimmed and yeast to be cropped from the top.
The full record
Open fermentation has its own catalogue entry with the detail this page summarises — causes, thresholds, related styles and evidence.
Open fermentation — Ferment in a vessel open to the air, allowing krausen to be skimmed and yeast to be cropped from the surface.
Still used at a number of traditional British, Belgian and German breweries. The blanket of CO₂ produced by an active fermentation protects the beer, so the contamination risk is lower than it sounds — though it is not zero, and open fermentation demands a clean room.
Whether it changes the beer is argued both ways. The clearest effects are practical: it makes skimming and top-cropping possible, and it allows a wide, shallow vessel geometry that differs from a tall cylindroconical.
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.