Insights into heterogenetic mechanism in physicochemical driving factors, microbial community and volatile metabolites during high-temperature Daqu fermentation by traditional stacking and shelf stacking.

Background: Research on shelf-stacking fermentation is growing, with the aim of reducing labor and improving Daqu stability, but it still falls short compared to traditional stacking fermentation, especially for high-temperature Daqu (HTD). The heterogenetic mechanisms underlying+ these two Daqu remain unclear.

Results: The improved micro-oxygen environment in shelf-stacking fermentation significantly reduced acidity and increased liquefaction and esterification activities compared to traditionally stacked HTD (HTD-T). These changes substantially impacted the bacterial community and its succession, though fungi were minimally affected. Specifically, shelf-stacked HTD (HTD-S) showed higher relative abundances of Weissella and Thermoactinomyces in later stages than HTD-T, whereas Bacillus and Kroppenstedtia prevailed under traditional conditions. Redundancy analysis indicated that moisture and acidity mainly drove the differentiation of the bacterial community. Shelf-stacking fermentation also reduced the contents of furfuryl alcohol, furfural, acetic acid and isovaleric acid. Thermoactinomyces, Aspergillus and Thermoascus significantly contributed to these changes in characteristic flavor compounds. Functional prediction further revealed that microbial communities in HTD-T demonstrated enhanced abilities in glycolysis, 2,3-butanediol synthesis and phenylalanine metabolism.

Conclusion: The findings provide potential control targets for precision regulation to improve the quality of shelf-stacked HTD and will contribute to mechanized HTD production. © 2025 Society of Chemical Industry.