This study investigated the microbial community in three-color sauce-flavor Daqu (black, yellow, and white) throughout their maturation processes, together with their physicochemical factors, culturable microbes, flavor components, and fermenting vitalities. Results from high-throughput sequencing revealed distinct microbial diversity, with more pronounced variations in bacterial community than in fungal community. Firmicutes and Ascomycota emerged as the most dominant bacterial and fungal phyla, respectively, during maturation. Genus-level analysis identified Kroppenstedia, Virgibacillus, and Bacillus as dominant bacteria in black Daqu, yellow Daqu, and white Daqu, severally, while Thermoascus was shared as the core dominant fungi for these Daqu. Physicochemical factors, particularly acidity, were found to exert a significant impact on microbial community. Kroppenstedtia was the key bacteria influencing the color formation of these Daqu. Furthermore, correlations between dominant microbes and flavor compounds highlighted their role in Daqu quality. Molds (Aspergillus, Rhizomucor, and Rhizopus), excepting Bacillus, played a crucial role in the formation of pyrazine compounds. Consequently, this study offers innovative insights into the microbial perspectives on color and pyrazine formation, establishing a groundwork for future mechanized Daqu production and quality control of sauce-flavor baijiu.

Baijiu is a traditional distilled liquor unique to China. Its distinctive flavor is shaped by the synergistic activity of complex microbial communities, among which yeasts play a central role in sugar metabolism, ethanol fermentation, and aroma synthesis. In recent years, the advancement of isolation and cultivation techniques, high-throughput sequencing, metagenomics, and multi-omics technologies has deepened our understanding of yeast community compositions, succession patterns, and functional characteristics during Baijiu brewing. Among these, Saccharomyces cerevisiae was recognized as the core ethanol-producing species and has been extensively studied for its metabolic traits and stress tolerance in Baijiu fermentation. Studies have shown that, in addition to S. cerevisiae, non-Saccharomyces yeasts such as Pichia, Wickerhamomyces, Saccharomycopsis, Kazachstania, and Candida et al. are widely distributed across strong-, sauce-, and light-flavor Baijiu and their respective starters (Daqu), exhibiting robust ester-producing capacities and stress resistance. These yeasts occupy distinct ecological niches throughout fermentation stages and engage in dynamic and environment-dependent interactions with lactic acid bacteria, molds, and other microbes. This review systematically summarizes yeast diversity, community structure, metabolic traits, key functional genes, microecological interactions, recent discoveries of novel yeast species, and advances in genetic engineering in Baijiu brewing. It further highlights future research priorities, including multi-omics integration, functional exploration of non-Saccharomyces yeasts, and synthetic biology-guided strain development, with the goal of supporting high-quality and intelligent Baijiu production.

Light-flavor Baijiu (LFB) fermentation is a representative spontaneous mixed-culture solid-state fermentation process in which sorghum is used as the raw material. Raw materials and microorganisms are crucial to the flavor formation and quality of LFB. However, the microbial and physicochemical dynamics of different sorghum varieties during LFB fermentation, as well as their impact on flavor compounds are still largely unknown. Herein, PacBio single-molecule real-time (SMRT) sequencing and headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry (HS-SPME-GC–MS) were applied to investigate microbial community succession and volatile flavor formation in glutinous/non-glutinous sorghum-based fermented grains during LFB fermentation. Fermented grains made of glutinous sorghum Liangnuo No. 1 (GLN) had higher bacterial α-diversity and lower fungal α-diversity than those with fermented grains prepared with non-glutinous red sorghum (NRS) (p < 0.05). The dominant microbial species were Saccharomyces cerevisiae, Acetobacter pasteurinus, and Lactobacillus helveticus, the latter two of which were the predominant bacteria observed at the end of fermentation in GLN and NRS, respectively. Moisture content and reducing sugar had a more significant impact on the microorganisms in GLN, while amino acid nitrogen, total free amino acids, and residual starch were the main driving factors driving the microbial community in NRS. The correlation network and discriminant analysis indicated that a relatively high content of 4-vinylguaiacol showed a significant positive association with significant differential microbial species in GLN. These results provided valuable insights for improving the quality of LFB.

Predominant odorants in modern and traditional types of Chinese xiaoqu liquor (Baijiu) were identified and compared by the combined use of gas chromatography−olfactometry, odor activity values (OAVs), and multivariate analyses. A total of 79 aroma compounds were identified in a typical modern type xiaoqu Baijiu (M) and a typical traditional type xiaoqu Baijiu (T), 42 of them had OAV > 1 in both M and T samples. The main differences between the two samples were obtained for the concentration of 23 aroma-active compounds. A total of 22 samples made by different brewing processes were analyzed to confirm the differences. Partial least squares discriminant analysis confirmed that 20 compounds could be used as potential markers for discrimination between modern type xiaoqu Baijiu and traditional type xiaoqu Baijiu. Their difference in content is between 1.5 and 17.9 times for modern type xiaoqu Baijiu and traditional type xiaoqu Baijiu. The results showed the aroma characteristics of modern and traditional type xiaoqu Baijiu clearly and comprehensively, which will provide guidance for modern Baijiu quality control and evaluation.