Rare short- and medium-chain fatty acid-producing anaerobes from raw soil play vital roles in formation of diverse flavour compounds of Jiangxiangxing Baijiu.

Pit mud is an essential habitat for diverse anaerobes, however, how pit mud of Jiangxiangxing Baijiu contributes to flavour is still unclear. The correlation between pit mud anaerobes and flavour compounds formation was investigated by analyzing flavour compounds and prokaryotic community of pit mud as well as fermented grains. Then scaling-down fermentation and culture-dependent approach were used to verify the effects of pit mud anaerobes on flavour compound formation. We found that short- and medium-chain fatty acids and alcohols, e.g., propionate, butyrate, caproate, 1-butanol, 1-hexanol, and 1-heptanol, were the vital flavour compounds produced by pit mud anaerobes. Pit mud anaerobes hardly migrated into fermented grains because of the low pH and low moisture of fermented grains. Therefore, the flavour compounds produced by pit mud anaerobes might enter fermented grains via volatilization. Moreover, enrichment culturing proved that raw soil was one of the sources for pit mud anaerobes, e.g., Clostridiumtyrobutyricum, Ruminococcaceae bacterium BL-4 and Caproicibacteriumamylolyticum. These rare short- and medium-chain fatty acid-producing anaerobes in raw soil can be enriched during Jiangxiangxing Baijiu fermentation. These findings clarified the role of pit mud during Jiangxiangxing Baijiu fermentation and revealed the key species involved in short- and medium-chain fatty acid-producing production.