Respiratory Deficiency in Brewing Yeast Strains-Effects on Fermentation, Flocculation, and Beer Flavor Components. José R. Ernandes, John W. Williams, Inge Russell, and Graham G. Stewart, John Labatt Limited, London, Ontario, Canada N6A 4M3. J. Am. Soc. Brew. Chem. 51:0016, 1993.

Respiratory sufficient (RS) and spontaneously arising respiratory deficient (RD) mutants from ale and lager brewing strains of Saccharomyces exhibited differences in both the rates and profiles of sugar uptake during low- or high-cell-density fermentations of brewer's wort. At low-cell density, the RD mutant displayed slower rates of fermentation and growth than did the RS wild-type strain. However, in high-cell density fermentations using yeast adapted to maltose utilization, the rates and profiles of maltose and maltotriose uptake did not differ substantially between RS and RD strains. Furthermore, the utilization of glucose by the RD mutant was faster than that by the RS strain. The amounts of esters and fusel oils in beers produced by RS and RD strains were different, and during wort fermentation, the RD mutant produced higher concentrations of diacetyl than did the RS strain. Extracted cell wall surface proteins from an RS yeast culture (flocculent) and its spontaneously generated RD mutant (nonflocculent) were found to be different when their protein bands were examined by sodium dodecylsulfate-polyacrylamide gel electrophoresis.

Keywords: Beer flavor, Fermentation, Flocculation, Petites, Saccharomyces, Wort, Yeast