Abstract
Repeated repitching is common in industrial ale fermentation, but yeast stress can accumulate across generations and reduce fermentation reliability, attenuation, and flavour consistency. This study evaluates yeast stress indicators during repeated repitching in industrial ale production. Yeast crops were collected and reused across multiple fermentation cycles under controlled wort composition, pitching rate, oxygenation, and temperature conditions. Viability, vitality, glycogen reserve, trehalose accumulation, membrane integrity, fermentation rate, sugar uptake, attenuation, pH reduction, ethanol yield, and stress-related by-products were monitored. The results show that early repitching generations maintained strong fermentation activity, while later generations showed reduced vitality, slower maltotriose utilization, and increased stress metabolite formation. Poor storage and excessive trub carryover intensified physiological decline. The study demonstrates that yeast stress monitoring is necessary for defining safe repitching limits in industrial ale production. Controlled yeast handling, storage, and generation tracking improve fermentation consistency and reduce flavour defects.