Trehalose—An Osmoprotectant and Stress Indicator Compound in High and Very High Gravity Brewing

Trehalose metabolism was studied in the yeast strain Saccharomyces cerevisiae var. uvarum (strain AJL 2036) during fermentation in normal gravity, high-gravity (HG), and very-high-gravity (VHG) worts. The maximum cellular trehalose concentrations were found to be proportional to original wort gravity. This effect was independent of the ethanol concentration in the fermenting wort. An increase in wort gravity resulted in both higher cellular trehalose contents and increased glycerol concentrations, irrespective of the carbohydrate used to increase the gravity. Aswort gravities increased, the cellular trehalose levels rose more than did the glycerol concentrations. This behavior was found to be a general osmotic stress response, but the effect was more marked in glucosesupplemented fermentations. Trehalose metabolism was confirmed to be strongly under nutrient control. This yeast strain's metabolism of trehalose was very different when under glucose-repressed or -derepressed conditions. In VHG worts, a significant accumulation of trehalose occurred very early in the fermentations. Yeast in these worts behaved as if derepressed despite the presence of significant amounts of glucose. It is proposed that trehalose is an important osmoprotectant and stress indicator compound for brewing yeasts fermenting HG or VHG worts. However, it is postulated that the efficiency of trehalose as an osmoprotectant is likely compromised by a repressed trehalose carrier protein during critical periods in the fermentations.