Rind-core microbial niche differentiation at centimeter-scale modulates the sensory quality of solid-state high-temperature Daqu.

High-temperature Daqu (HTD) is a vital microbial starter for Moutai-flavor Baijiu, providing the essential enzymes and flavor precursors required for fermentation. However, restricted mass and heat transfer during the solid-state process drive pronounced spatial heterogeneity across the Daqu brick, yet how this niche differentiation modulates HTD quality remains elusive. In this study, we analyzed a comprehensive dataset (n = 134) spanning 12 production batches, performing centimeter-scale characterization of physicochemical properties and microbial succession in both high-quality and ordinary-quality HTD. Our results showed that while whole-sample analysis failed to detect differences between high-quality and ordinary-quality Daqu, spatial partitioning revealed that ordinary-quality rind had significantly lower acidity than high-quality rind during the early fermentation stage (S1, days 9-12), with no difference in the core. Furthermore, significant microbial differentiation was observed between the rind and core of HTD, with this spatial divergence occurring at an accelerated rate in ordinary-quality samples during fermentation. Redundancy analysis (RDA) and laboratory validation further confirmed that these micro-ecological variations were primarily driven by gradients in acidity and water content Our study highlights the importance of considering centimeter-scale microbial heterogeneity, providing insight into its relationship with microbial succession rates and how these factors contribute to the final quality of HTD.