Pit-wall mud (PWM) fosters bacterial communities involved in Baijiu production. PWM varies depending on pit age and height. In this study, we explored the bacterial communities in PWM and factors driving their evolution. The abundance and diversity of bacterial communities were low in new PWM (NPWM). In old PWM (OPWM), similar but diverse bacterial communities were observed at different heights. Lactobacillus was the predominant genus in NPWM, and Caproiciproducens, Aminobacterium, Hydrogenispora, Lactobacillus, Petrimonas, Syntrophomonas, and Sedimentibacter were the dominant genera in OPWM. A decrease was noted in the abundance of Lactobacillus, which indicated evolution. Among all the physicochemical properties, pH had the highest degree of interpretation with an R² value of 0.965. pH also exerted the strongest effect on bacterial communities. The path coefficients of pH on bacterial community diversity and abundance were 0.886 and 0.810, respectively. Caproiciproducens and Clostridium sensu stricto 12 metabolized lactic acid, inhibiting the growth of Lactobacillus at a suitable pH, which led to the maturation of PWM. Our findings enrich the literature on the evolution of bacterial communities in PM and the maturation of PM.

The succession of microbial communities during the fermentation process in sesame-flavored Baijiu cellars profoundly influences the flavor profile of the liquor. However, the key factors driving microbial succession in these cellars remain unclear. This study focuses on the fermentation process of sesame-flavored Baijiu Zaopei in traditional Tongcheng cellars. Samples were collected from the surface, middle, and bottom of the cellar, categorized by fermentation time. Various techniques were employed to analyze the physicochemical properties (including moisture, ethanol, total acid, starch, and reducing sugars), flavor compounds (volatile substances and amino acids), and microbial communities (bacteria and fungi) of the Zaopei during fermentation. A total of 68 flavor compounds were detected, with 16 key flavor compounds and 16 amino acids identified. Microbiologically, the Lactobacillus genus dominated in the later stages of fermentation, while the Issatchenkia species were the predominant fungi. Correlation analysis indicated that environmental factors play a significant role in driving microbial community succession. Acetobacter, Staphylococcus, Pichia, Bacillus, and Kroppenstedtia species may contribute to the synthesis of key flavor compounds. The relative contents of acetic acid, 2-phenylethyl ester, and Benzenepropanoic acid ethyl ester were influenced by multiple microbial groups, suggesting a synergistic fermentation effect. PICRUSt2 predictions revealed significant differences in 41 KEGG pathways at level 2 and 293 pathways at level 3 across different fermentation intervals. These pathways are primarily associated with amino acid, ester, and nucleotide metabolism, as well as bacterial transcription, translation, and signal transduction. This research provides a theoretical foundation for understanding the fermentation mechanisms of sesame-flavored Baijiu.

Fermented soybean paste, a traditional high-salt condiment, faces challenges in standardization and quality control due to its reliance on natural fermentation. This study systematically evaluated the effects of a defined starter culture, Tetragenococcus halophilus CICC 10286, on soybean paste fermentation by comparing natural fermentation (NF) and fortified fermentation (FF). Compared with NF, FF maintained a higher moisture in the later stage (NF-LS: 50.30%; FF-LS: 60.08%) and lower total acid levels in the middle and later stages (NF-MS: 1.58 g/100 g; FF-MS: 0.96 g/100 g; NF-LS: 2.23 g/100 g; FF-LS: 1.11 g/100 g). Although protein degradation was more pronounced in the FF group at the midpoint (p < 0.0001), the lower accumulation of amino acid nitrogen suggests a potential shift in nitrogen metabolism, possibly toward enhanced transamination or deamination processes. Free amino acid profiling indicated that FF facilitated earlier accumulation of umami and sweet amino acids, but the total free amino acid content in the later stage was lower. Specifically, Glu and Asp reached 724.47 nmol/L and 305.52 nmol/L, respectively, in NF-LS, whereas the corresponding values in FF-LS were 397.16 nmol/L and 275.46 nmol/L. Meanwhile, Pro reached 337.81 nmol/L in FF-MS, indicating earlier accumulation of some amino acids under FF. Notably, the proportion of bitter amino acids in the FF group was reduced in the later stage. Microbial community analysis showed that FF promoted the enrichment of Tetragenococcus and halotolerant bacteria, such as Halomonas, at the midpoint, and increased the relative abundance of the aroma-producing yeast Zygosaccharomyces (NF-MS: 37.73%; FF-MS: 65.11%). Functional prediction based on PICRUSt2 suggested a higher predicted abundance of genes involved in pyruvate metabolism and branched-chain amino acid degradation in the FF group. These findings demonstrate that T. halophilus CICC 10286, as a starter culture, can effectively modulate the fermentation of soybean paste, providing a scientific basis for developing standardized and quality-controlled fermentation processes.