Impact of rice koji enzymatic mashing and sequential co-fermentation by fruit peel-isolated yeast on wort composition, volatile profiles, and sensory characteristics of rice beer

While rice is an attractive cereal for low-alcohol beverage innovation, inefficient starch saccharification remains a production bottleneck compared to traditional barley brewing. This study developed an integrated strategy combining rice koji-driven mashing and sequential co-fermentation with Saccharomyces cerevisiae and Hanseniaspora vineae to address the above limitations and improve the quality of rice beer. Rice koji exhibited robust hydrolytic activity during the initial mashing stage (45°C), significantly changing the wort carbohydrate composition with a 2.6-fold increase in glucose concentration compared to the control. The modified sugar profile and sequential inoculation fundamentally shifted yeast population dynamics. Unlike barley-based fermentation where S. cerevisiae dominated, the rice-based wort allowed both yeasts to maintain comparable populations, likely due to lower ethanol accumulation. This microbial interaction significantly enriched volatile compounds, particularly acetate esters. Specifically, compared to the single strain fermentation, 2-phenylethyl acetate (floral note) increased from undetectable levels to 15.91 mg/L in the sequential co-fermentation group. Correspondence analysis correlated sequential co-fermentation with floral aftertaste attributes, reflecting higher sensory scores in overall acceptability for the developed rice beer. Overall, the synergy between koji-assisted enzymatic hydrolysis and yeast population modulation provides a robust pathway for enhancing the quality and aromatic complexity of rice-based beverages.