Abstract
Sour beer fermentation depends on controlled interaction between lactic acid bacteria and mixed yeast cultures, which together shape acidity, attenuation, aroma complexity, and maturation stability. This study investigates sour beer fermentation control using selected lactic acid bacteria and mixed yeast cultures. Controlled fermentations were prepared with defined inoculation timing, culture ratios, wort composition, temperature, oxygen exposure, and maturation duration. Lactic acid production, pH decline, yeast viability, sugar utilization, ethanol formation, ester development, phenolic expression, volatile acidity, turbidity, and sensory balance were monitored. The results show that coordinated bacterial and yeast activity produced balanced acidity and complex aroma development. Excessive bacterial dominance caused sharp acidity and reduced flavour integration, while weak bacterial activity produced insufficient sour character. Mixed yeast cultures improved aroma depth but required careful control to avoid unstable attenuation. The study demonstrates that sour beer quality depends on managing microbial timing and culture balance across fermentation and maturation.