Identifying Key Microorganisms During the Low-Temperature Incubation Phase in the Production of Medium-High Temperature Daqu

Daqu, an essential component in Baijiu production, is classified into low-temperature Daqu, medium-high temperature Daqu, and high-temperature Daqu based on the maximum achievable temperatures during the production process. Medium-high temperature Daqu is used for brewing strong-flavor Baijiu. The low-temperature incubation period, the first stage of indoor cultivation in the production process of medium-high temperature Daqu, is crucial for the growth and reproduction of various brewing microorganisms. This study examined the physicochemical indexes, microbial composition, and volatile compounds during the low-temperature incubation period of Daqu. As the temperature of Daqu increased, the acidity initially rose and then decreased, starch content continued to increase, alcoholic power increased continuously, esterifying power almost doubled and glycosylated amylase decreased. A total of 46 major volatile compounds, including alcohols (14), esters (18), acids (3), furans (1), aldehydes (5), phenols (2), ketones (2), and pyrazines (1), were identified. Phenylethyl alcohol exhibited the highest concentration and the greatest variation. Among them, Lactobacillus and Issatchenkia were identified as the most abundant bacterial and fungal genera, respectively. Trichosporon showed the strongest positive correlation with the increase in butanol content, and Aspergillus exhibited significant positive correlations with many types of important physicochemical indexes of Daqu. Wickerhamomyces, Saccharomyces, and Alternaria disappeared in the later stage of the low-temperature incubation period. These findings provide important evidence for better understanding and optimizing the crucial low-temperature incubation period, ultimately enhancing the quality of Daqu production.