fermentation mode
Open fermentation
Fermenting in uncovered vessels, still practised in parts of Czech, German and British brewing.
The full record
Open fermentation has its own catalogue entry with the detail this page summarises — mechanism, temperatures and what goes wrong.
Open fermentation — Ferment in a vessel open to the air, allowing krausen to be skimmed and yeast to be cropped from the surface.
Counterintuitively low-risk in practice: the rising CO₂ blanket and the vigorous krausen protect the beer during active fermentation. It allows yeast to be cropped from the surface and is claimed to produce a cleaner ester profile, though the evidence for that is more traditional than experimental.