Application of High-Temperature Daqu with Controlled Temperature and Humidity in Baijiu Brewing

To achieve automation of high-temperature Daqu production for jiang-flavor baijiu, temperature- and humidity-controlled rooms were employed. High-throughput sequencing and headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) were used to detect the microbial communities and volatile flavor components of Jiupei (fermented grains) made with temperature- and humidity-controlled Daqu or traditional Daqu during the sixth round of baijiu brewing, respectively. The results showed that Firmicutes was the dominant bacterial phylum in the experimental (67.95%-86.04%) and control (81.24%-89.04%) cellars during the entire fermentation process. Ascomycota was the absolute dominant fungal phylum in both cellars, with relative abundance exceeding 97%. During the entire fermentation process, the dominant bacterial genera in the experimental cellar were Kroppenstedtia (18.50%), Virgibacillus (17.00%), and Thermoactinomyces (13.25%), and the dominant fungal genera were Monascus (25.93%), Thermomyces (17.75%), and Byssochlamys (15.78%). The dominant bacterial genera in the control cellar were Kroppenstedtia (30.05%), Virgibacillus (20.84%), and Oceanobacillus (15.00%), and the dominant fungal genera were Pichia (50.74%), Monascus (14.18%), and Byssochlamys (8.97%). A total of 97 volatile flavor compounds were identified in Jiupei, and the total content of volatile flavor compound was 2 143.29 and 2 521.04 mg/kg in the experimental and control cellars, respectively. Using the cutoff of variable importance in the projection (VIP) values greater than one, 29 significantly differential volatile flavor compounds were identified. Spearman analysis was used to calculate the correlation between the significantly differential metabolites and the dominant microorganisms, revealing that the bacterial genera significantly positively correlated with the majority of ester compounds had a higher relative abundance in the experimental cellar compared with the control cellar, whereas the bacterial genera with a higher relative abundance in the control cellar, such as Pichia and Kroppenstedtia, were mainly positively correlated with most alcohol compounds. Analysis of the changes in microbial communities and volatile flavor compounds during the production of Daqu revealed that applying temperature- and humidity-controlled Daqu in the sixth round of baijiu brewing had a positive effect on the formation of most ester compounds. The metabolic function prediction of bacterial flora using the PICRUSt2 software showed that temperature- and humidity-controlled Daqu exhibited comparable safety and functionality to traditional Daqu in baijiu production. This research will contribute to the transformation and upgrading of the mechanized brewing mode for jiang-flavor baijiu.