Assessment of added glutathione in yeast propagations, wort fermentations, and beer storage

Glutathione (GSH) is one of the most abundant low-molecular-weight thiols found in living cells. Concentrations varying from 8 to 37 nmol/mg of cells were measured in brewing yeast. While other studies emphasize the key role of GSH in the response of some genetically modified yeasts to different stresses, our results show that GSH added to the yeast propagation medium has no significant impact on the growth of most brewing yeast strains. In high-gravity primary fermentations, a slight positive effect was observed during the first week with only two (lager) yeast strains. Added to phosphate buffer or beer, GSH imparts a reducing activity similar to that of ascorbic acid, but it proves to be a much less powerful antioxidant than phenolic compounds. Whatever the chosen step for spiking, beers aged in the presence of GSH were characterized by strong sulfurous off-flavors, despite a mere 6% degradation of the tripeptide.