Abstract

The first fermentation round serves as the critical starting point for the formation of the sauce-flavor style. However, the spatial heterogeneity and intrinsic relationships between the microbial community, physicochemical properties, and flavor compounds in the first-round fermented grains remain unclear. In this work, microbial communities and volatile compounds across different layers of the fermentation pit were investigated. Results showed both acidity and ethanol content decreased with increasing depth. Lactobacillus was the dominant bacterial genus across all layers, whereas the dominant fungal genera exhibited marked spatial stratification: Trichosporon prevailed in the bottom layer, while Pichia dominated the middle and upper layers. Ethyl phenylacetate served as the backbone aroma compound across all layers, but distinct layer-specific flavor compounds were identified. Nonanal, potentially correlated with Trichosporon, was the key flavor compound in the bottom layer; phenolic compounds characterized the middle layer, and Pichia-associated esters such as isoamyl acetate dominated the upper layer. Correlation analysis confirmed significant associations between specific microbial taxa and ester accumulation. Notably, Pichia and Trichosporon exhibited opposing correlations with multiple flavor compounds, suggesting metabolic differentiation. This study clarified the spatial distribution of microorganisms and flavors and provided correlational insights into flavor formation in traditional baijiu fermentation.

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