The Importance of Wort Composition for Yeast Metabolism During Accelerated Brewery Fermentations

The volumetric productivity of the beer fermentation process can be increased by using a higher pitching rate (i.e., higher inoculum level). Next to this, high-gravity brewing has become a standard strategy for brewers to increase their productivity. However, both technologies can have a significant effect on yeast metabolism. In this study, high-gravity and high-cell-density fermentations were combined, and their impact on yeast physiology and flavor compound production was evaluated. Additionally, an attempt was made to decrease the production of total diacetyl during accelerated fermentation systems by optimization of the free amino nitrogen content of the wort. Higher wort density resulted in decreased yeast viability, which correlated to increased expression levels of stress-related genes and higher levels of trehalose. More than wort density, the relative amounts of different assimilable sugars have a drastic effect on both yeast fermentation performance and flavor compound production. Worts with high amounts of sucrose had a stimulating effect on the uptake of amino acids, yeast growth, glycogen formation, recycling of trehalose, ethyl ester synthesis, and the turnover rate of total diacetyl. Yeast exposed to high levels of sucrose experienced more osmotic stress and stress related to stationary phase than other high-gravity worts. Although sucrose, compared with maltose, had a stimulating effect on ATFl expression, a remarkable decrease in acetate esters was observed. Considering the adverse effects of sucrose on the yeast performance, it is advisable to avoid high concentrations of these fast-food sugars and to use a combination of sucrose and maltose syrups as a way to increase the wort density.