DETERMINATION OF YEAST VIABILITY

Abstract

A new technique for the determination of yeast viability, by cultivation on haemacytometer slides followed by counting the microcolonies, gave a demonstrably true estimate of the percentage of cells which were able to reproduce. By comparison with this method, staining techniques correctly estimated the percentage of viable cells In fresh yeasts, but overestimated the percentage of viable cells in old yeasts. Gelatin plate counts always underestimated the percentage viability. With some brewery yeasts it was possible to demonstrate by slide culture that the dilution necessary for a plate count was lethal to a large proportion of the cells. The gelatin plate method therefore gave very low and erroneous results for the viability of these yeasts. Slide culture was also found to be useful for the enumeration of chain-forming yeasts in a mixed culture.