Regulation of pile-forming duration drives microbial community succession and flavor metabolism in sauce-flavor baijiu brewing

Stacking fermentation is a critical procedure in sauce-flavor baijiu production, and pile-forming operations (from pile initiation to pile completion) play important roles in enriching microorganisms and promoting heap temperature increases. However, the impacts of different pile-forming durations (PFD) on the physicochemical parameters, volatile compounds, and microbial composition of fermented grains remain unclear. Here, the physicochemical parameters, volatile compounds, and microbial communities of fermented grains were comprehensively investigated across three PFD groups (PFD_72h, PFD_48h, and PFD_24h) during the 4th-6th rounds. The three groups showed similar dynamic patterns in total titratable acidity, moisture, reducing sugar, starch, organic acids, and volatile compounds. Compared with PFD_72h, PFD_24h and PFD_48h exhibited higher initial temperatures and faster heating rates during stacking fermentation, whereas PFD_72h showed higher total titratable acidity and lactic acid levels at the end of pit fermentation (CJ stage). The microbial community composition and succession patterns were similar among PFD groups, while dominant genera (Thermomyces , Thermoascus , and Saccharomyces etc.) showed higher relative abundances in the PFD_48h and PFD_24h groups at the end of stacking fermentation (PD stage). Co-occurrence networks differed in structure and keystone taxa, with the PFD_72h network showing greater complexity and stability in the 4th and 6th rounds. Redundancy analysis identified temperature and acidity as key drivers of microbial community variation. Metabolic correlation and functional prediction analyses showed that Acetilactobacillus , Pichia , and Kazachstania were significantly associated with acetic acid, ethanol, and ethyl acetate. These findings clarify PFD effects on fermentation characteristics and provide insights into regulating stacking fermentation in sauce-flavor baijiu production.