Characterization of fermentation parameters, volatile compounds and microbial community structure of fermented grains in the upper and lower layers during strong-flavor Baijiu fermentation.

Strong-flavor Baijiu (SFB) is produced using a solid-state fermentation system, but the impact of stratified fermented grains on fermentation remains unclear. Therefore, in a typical distillery plant, we evaluated the physical and chemical composition, volatile compound profile, and microbial community of fermented grains in SFB both above (FG-A) and below (FG-B) the Huangshui line. Significant differences in fermentation parameters between FG-A and FG-B were observed after 30 days of fermentation (P < 0.05). Additionally, the partial least squares projection to latent structure discriminant analysis (PLS-DA) revealed distinct differences in volatile compounds between FG-B and FG-A, identifying 26 discriminant markers. The diversity of short-chain fatty acids (SCFAs) and their esters were higher in FG-B compared to FG-A. Furthermore, microbial diversity and abundance have differed significantly between the two layers of fermented grains (P < 0.05), included 17 differential genera. Correlation and pathway enrichment analyses indicated that the higher SCFA content in FG-B could be attributed to the greater abundance of acid-producing microorganisms compared to FG-A. This study highlights the differences between the two layers of fermented grains in SFB fermentation, offering new insights into solid-state fermentation and expanding the current understanding of the traditional SFB fermentation process.