Open and closed fermentation
Term from the Brauwerkstatt brewing glossary, category “Fermentation and yeast”.
Explanation
In open fermentation the beer ferments in an open vessel and the yeast can be skimmed straight from the surface – traditional for weissbier and English ales. In closed fermentation the vessel is sealed with an airlock. For homebrewers this is safer because fewer microbes and less oxygen get in.