Dynamic diversification of bacterial functional groups in the Baiyunbian liquor stacking fermentation process

The stacking fermentation (SF) process is a bridge between Daqu making and alcoholic fermentation in the pits. Revealing the dynamic diversification of the microbial functional groups in this process is of vital importance to unfold the mechanism of Baiyunbian liquor flavor, and improve the quantity and production of the traditional Chinese liquor fermentation process. A total of 142 strains of bacteria were isolated from the Baiyunbian liquor SF process, which were divided into 17 species and two subspecies. These isolated bacteria could hydrolyze the main carbon resources such as starch, protein, cellulose, lignin, and fat as well as produce acetic acid, lactic acid, or butyric acid. Our results indicated that the dynamic variations of the bacterial functional groups revealed their specific functions in the Baiyunbian SF process. Interestingly, although the bacterial bio-diversity decreased during the SF process, the total bacterial biomass increased at the end, in which the biomass of the starch degrading bacteria was dominate throughout the whole SF process. Among the identified bacteria, B.licheniformis and B.subtilis contributed the most biomass and functionalities during the Baiyunbian SF process, playing important roles in the formation of the Maotai-flavor. Our study revealed the bio-diversity of the microbial functional groups in the Baiyunbian liquor SF process and the mechanism of the Baiyunbian liquor flavor formation, providing valuable guidance to improve the traditional Chinese liquor fermentation process. It could also act as an attempt to turn the present manufacturing process to standardized procedures.