Abstract
Elevated wort gravity increases brewing productivity but exposes yeast cells to osmotic stress, ethanol toxicity, nutrient limitation, and altered sugar uptake patterns. This study investigates yeast stress response and ethanol yield under elevated wort gravity conditions. Controlled fermentations were conducted using wort with different extract concentrations while maintaining constant yeast strain, pitching rate, oxygenation, and temperature. Yeast viability, trehalose accumulation, glycerol formation, sugar consumption, ethanol production, attenuation, pH reduction, fermentation time, and stress-related by-products were monitored. The results show that higher wort gravity increased early osmotic stress and later ethanol stress, leading to slower maltotriose utilization and reduced conversion efficiency at the highest extract level. Balanced nitrogen availability and oxygenation improved yeast adaptation, supported higher attenuation, and reduced sluggish fermentation. The study demonstrates that ethanol yield under elevated wort gravity depends on yeast physiological tolerance rather than extract concentration alone. Controlled nutrient management improves high-gravity fermentation reliability.