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Beer Fermentation
Yeast Collection
Removal of excess yeast from beer at the end of primary fermentation is necessary to minimize the load on the filter medium, to prevent yeast metabolism and autolysis, and to provide a source of yeast for pitching subsequent brews.
The time it takes for autolysis to set in depends on temperature and the strain of yeast. Yeast will stay in good condition at cold temperatures. Thus, separating the beer from the layer of sediment yeast at the end of primary fermentation is particularly important, especially when fermentation is carried out at elevated temperatures. Many of the off-flavors in beer that are described as "yeasty" are due to the excretion of fatty acids by the yeast, a process which is accelerated at high temperatures (27).
Click on the following topics for more information on beer fermentation.