Abstract
Strong beer production exposes yeast cells to high ethanol concentration, osmotic pressure, nutrient limitation, and prolonged fermentation stress, which can reduce attenuation and flavour consistency. This study examines yeast stress tolerance during high-ethanol fermentation in strong beer production. Controlled fermentations were conducted using high-gravity wort under fixed pitching rate, oxygenation, nutrient level, and temperature conditions. Yeast viability, membrane integrity, trehalose accumulation, glycerol production, sugar utilization, ethanol yield, attenuation, pH reduction, and stress-related aroma compounds were monitored. The results show that ethanol stress increased during late fermentation, slowing maltotriose uptake and reducing yeast vitality. Strains with stronger membrane stability maintained better attenuation and produced fewer harsh alcohol notes. Balanced nutrient supply and oxygen management improved stress adaptation and fermentation completion. The study demonstrates that high-ethanol beer quality depends on matching yeast tolerance with wort strength, nutrition, and temperature control to maintain stable fermentation performance.