Effects of Huangshui on the links of pit age to microbial–flavor coupling in Nongxiangxing Baijiu fermentation

Pit age is a key factor shaping microbial succession and flavor formation during Nongxiangxing Baijiu (NXB) fermentation, the ecological coupling among pit mud (PM), Huangshui (HS), and Jiupei (JP) remains unclear. Here, we analyzed the physicochemical properties, microbial communities, and volatile organic compounds (VOCs) of PM, HS, and JP collected from fermentation pits used for 5 and 30 years. Further, mantel tests and co-occurrence network analyses were performed to examine associations among environmental factors, microbiota, and flavor metabolism. The results showed that PM from the 30-year fermentation pits exhibited a more mature physicochemical profile and a more favorable niche for microbial colonization. Lactobacillus was the predominant bacterial genus in JP and HS, whereas Methanosarcina and Fastidiosipila were enriched in PM; Pichia was more abundant in HS, while Monascus was characteristic of PM. Esters were the dominant VOCs in all samples, and HS and JP displayed highly similar volatile compositions. Notably, Lactobacillus remained a core taxon across pit ages, whereas fungal interactions shifted from competitive to cooperative patterns in older fermentation pits. The above findings clarify microecological contributions to flavor formation, and further to offer a theoretical basis for process optimization and quality regulation in industrial Baijiu production.