Microorganisms in Daqu: a starter culture of Chinese Maotai-flavor liquor

Maotai-flavor liquor, a famous traditional Chinese drink, is distilled from fermented sorghum in the southern province of China. Moreover, it is of interest as one of the few examples of liquor distilled from the product of a fermentation using a wild microflora starter. Daqu is the starter of this fermentation process. Daqu is a mixture of two components: milled wheat and a complex microbial community. The composition and the effects of this microbial group are largely unknown. In this study, we have analysed the constituents of the microbial community and the development of microorganisms in the industrial Daqu preparation and ripening process. More than 200 colonies were isolated and characterized. The isolates were discriminated by phenotypic and conventional biochemical taxonomic methods. The results revealed the presence of bacteria, moulds and yeasts. Bacteria consist of Bacillus, Acetobacter, Lactobacillus, and Clostridium, among which Bacillus strains were found to be predominant. Moulds consisted of Aspergillus, Mucor, Rhizopus, Monascus and Trichoderma, and Aspergillus strains were found to be predominant in the six different biotypes. Yeasts comprised Saccharomyces, Hansenula, Candida, Pichia, and Torulaspora. The most frequently isolated yeasts belonged to the genus Saccharomyces. The microbial diversity shift showed that the microbial genera changed with increasing ripening time. Knowledge of the microbial diversity in Daqu provides a basis for microflora management and understanding of the role of microbes in the Daqu production process, and the contribution of Daqu performed as a starter culture to Maotai-flavor liquor.