Tempo-spatial dynamics of physicochemical properties and microbial communities in high-temperature Daqu during the fermentation process

High-temperature Daqu (HTD) is the starter for sauce-flavor Baijiu, produced through stacked solid-state fermentation. At the end of fermentation, white, yellow, and black Daqu are typically formed in different layers of the stack, but the mechanisms behind their formation remain unclear. This study compared tempo-spatial dynamics of physicochemical properties, metabolites, and species-level microbial communities throughout HTD fermentation. Different layers of HTD remained similar during the initial five days of fermentation, but gradually exhibited significant physicochemical and microbial differentiation in the later stage (days 8-40). The upper-layer Daqu exhibited remarkably higher saccharification and liquefaction enzyme activities than the other layers. Thirty-nine differential metabolites and thirteen microbial biomarkers were identified at different layers. The microbial co-occurrence networks, correlations of dominant microbes with specific metabolites, and physicochemical factors significantly shaping the microbial communities in different layers of HTD were illustrated. This study provides valuable insights into the fermentation mechanisms of different HTD types.