Ecological Niche Differentiation in 3D Expanding Stacks: A Key Mechanism for Enhancing Yeast Community Complexity in Sauce-Flavor Baijiu Fermentation

Stacking fermentation of sauce-flavor Baijiu forms a 3D stratified solid-state bioreactor. The artisanal operations and environment create four microniches, driving yeast community complexity that regulates ethanol production, flavor biosynthesis, microbial balance, and Baijiu quality, yet yeast spatiotemporal dynamics and species-specific flavor roles remain unclear. Using amplicon sequencing and monoculture fermentations, this study mapped yeast distribution and quantified flavor contributions. Yeast richness peaked at 30 genera, dominated by Saccharomycopsis (41.88%), Pichia (17.28%), and Torulaspora (12.58%), with dynamics correlating with moisture, temperature, and acidity ( p < 0.05). Key isolates had distinct traits: P. kudriavzevii JNPK produced floral and fruity flavor esters/alcohols, P. manshurica JNPM generated aldehydes, S. fibuligera JNSF produced fewer volatile organic compounds (VOCs), and T. delbrueckii JNTD produced organic acids/tetramethylpyrazine (all critical for aroma). This study provides theoretical support for optimizing yeast application in sauce-flavor Baijiu fermentation.