Abstract
Light-flavour Baijiu is a type of Chinese liquor with a pure and mild flavour produced by traditional spontaneous solid-state fermentation. The flavour of this liquor has been found to vary in the different periods of annual production. To explore the factors affecting flavour, the microbiota of the surrounding environment, starter and fermentation process in different periods were investigated. Results showed that the ester content and acidity of light-flavour Baijiu were significantly lower when annual production was resumed after a summer break. HCA plot of volatile flavour profile and bacterial PCoA results indicated that the differences occurred at later stages, mainly due to different structures of Lactobacillus. Correlation analysis by O2PLS indicated that Lactobacillus positively correlated with esters. Species-level analysis showed that the lack of L. acetotolerans on the surface of the jar might cause a lag in fermentation and lower ester content. Thereafter, L. acetotolerans was revived during fermentation and enriched on the surface of the jar, which promoted ester formation. As important sources of L. acetotolerans, the air and fermentation jars played a critical role during fermentation. Therefore, this systematic study on environmental microbial ecology is valuable for quality control and to explore environmental microbiota functions during spontaneous fermentation.
Highlights
Over thousands of years, humans have optimized the conditions including temperature, moisture, and salinity to promote the growth of certain microbial communities and obtain various fermented foods such as cheese, alcoholic beverages, sourdough, soy sauce, and vinegar[1,2]
The annual production is divided into three periods: (1) Lipai period (LP) refers to the beginning of a production cycle in September after the summer production break, (2) Tiaopai period (TP) refers to the last period of production before production break in the summer, (3) Yuanpai period (YP) refers to the production period between LP and TP
The ester content in Baijiu during LP was about 2.93 g/L, which was significantly lower than 5.07 g/L in YP (p < 0.01)
Summary
Humans have optimized the conditions including temperature, moisture, and salinity to promote the growth of certain microbial communities and obtain various fermented foods such as cheese, alcoholic beverages, sourdough, soy sauce, and vinegar[1,2]. The traditional process of Baijiu mainly includes material preparation, Daqu (starter) preparation, alcoholic fermentation, solid-state distillation, and aging[6]. The alcoholic fermentation of light-flavour Baijiu is carried out in pottery earthen jars instead of mud pits, which are used for the other two types of Baijiu. Throughout the annual production, it was found in common that the ester content in light-flavour Baijiu produced during LP was found to be significantly lower than that produced during YP and TP, the same Daqu was used. Environmental microorganism from fermenters, tools, staffs, and air in the material preparing room are thought to cause a difference to the flavour and quality during LP. We attempted to provide an insight into the composition and dynamics of environmental microbial communities present in different alcoholic fermentation periods. These findings should be immensely helpful for exploring environmental microbiota functions during spontaneous fermentation
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