Abstract
Dissolved oxygen control during early lager fermentation is essential because oxygen availability influences yeast growth, membrane synthesis, fermentation rate, attenuation, and flavour stability. This study examines the effect of dissolved oxygen level on early-stage lager fermentation under controlled brewing conditions. Lager wort was oxygenated at selected concentrations before pitching, while wort composition, yeast strain, pitching rate, and fermentation temperature were kept constant. Yeast cell growth, oxygen depletion, sugar utilization, ethanol formation, pH reduction, vicinal diketone development, attenuation, and fermentation time were evaluated. The results show that insufficient oxygen limited yeast growth and slowed fermentation, while excessive oxygen increased oxidative stress indicators and altered flavour precursor formation. Moderate oxygenation supported stable yeast metabolism, improved attenuation, and reduced fermentation variability. The study demonstrates that dissolved oxygen should be managed as a precise process-control variable rather than a routine pre-fermentation step. This improves consistency in lager production.