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Brewers Yeast
Yeast Pure Cultures
The process of culturing yeast strains involves isolation of a single yeast cell, maintenance of yeast cultures, and the propagation of the yeast until an amount sufficient for pitching is obtained.
The Isolation of Pure Cultures
Pure yeast cultures are obtained from a number of sources. Most often, the yeast is already in use in the brewery, but it can also be obtained from other breweries, commercial distributors, or culture collections. Various procedures are used to collect pure cultures, including culturing from a single colony, a single cell, or a mixture of isolated cells and colonies.
The Maintenance of Pure Cultures
Once yeast has been selected, accepted, and fully proven for use in brewing, it is essential that a pure culture (working master culture) is maintained in the laboratory yeast bank for prolonged periods. Some of the more common methods used for maintaining the purity and characteristics of the yeast culture are subculturing, desiccation, and lyophilization.
The Propagation of Pure Cultures
The objective of propagation is to produce large quantities of yeast with known characteristics for the primary role of fermentation, in as short a time as possible. Most brewers use a simple batch system of propagation, starting with a few milliliters of stock culture and scaling up until there is enough yeast to pitch a commercial brew. Scale-up introduces actively growing cells to a fresh supply of nutrients in order to produce a crop of yeast in the optimum physiological state.
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