Bacterial Functions and Cooperative Mechanism in Major Aroma-Types Baijiu (Chinese Liquor) Solid-State Fermentation: From Ecological Correlation to Metabolic Causality

Baijiu, a Chinese liquor stands out for its distinctive flavor derived from solid-state fermentation and a diverse microbial community as compared to other liquors like whiskey and brandy. The current research on Baijiu fermentation has focused on microbial dynamics and the development of volatile compounds, while the specific roles of individual bacteria remain less understood. This review systematically benchmarks functional bacteria across major aroma-types (Sauce-, Strong-, Light-, and Rice-flavor), proposing a Constraint-Driven Functional Assembly hypothesis to elucidate how environmental factors shape functional guilds. It explores how these bacteria contribute to substrate utilization efficiency, conversion of the volatile compounds, and enhancements to Baijiu quality. In large-scale solid-state fermentation of Baijiu, individual bacteria are keystone drivers of substrate utilization, aroma production, flavor, and act as ecological engineers that accelerate fermentation kinetics. Crucially, by establishing the Key Taxa–Metabolic Pathway–Flavor linkage, this review facilitates a transition from ecological correlation to metabolic causality. Moreover, analyzing advancements in microbial research, fermentation technologies, and metabolic regulation provides insights into optimizing bacterial functions to enhance both the efficiency and sensory of Baijiu production. Finally, functional bacteria from Baijiu fermentation hold promise for applications beyond the beverage industry, including use in functional foods as potential probiotics.