Daqu is a saccharifying starter for brewing Baijiu, and it is a consortium of microorganisms, enzymes and substances formed by natural fermentation under completely open conditions, which is the product of the joint action of a microbial community. Microorganisms are the core of Daqu, as they determine enzymes, which in turn determine compounds. Current research on Daqu involves various aspects related to microorganisms, enzymes, and compounds, such as sensory characteristics, microbial community succession, enzyme properties, physicochemical properties, volatile compounds, and non-volatile compounds. Research on microorganisms in Daqu focuses on the structure succession and function of microbial communities, and their correlations with sensory characteristics, enzymes, physicochemical properties, volatile compounds, and non-volatile compounds. This article systematically reviews the current status of and progress in fungal research in Daqu based on the literature published over the past decade, aiming to ensure that the Baijiu industry stays informed about the trends in research on Daqu fungi, thereby advancing relevant research work and improving this industry’s technical level.

The central regions with the most significant sensory characteristics (denoted as HXH, HRA and QCU, respectively) of three kinds of Fengxiangxing Daqu, namely, Hongxinqu, Huairangqu and Qingchaqu, were characterized for microscopic features, physicochemical properties, fungal communities, and volatile substances. The significant differences in and the correlation between fungal communities and physicochemical properties and volatile substances were analyzed. The results showed that the core fungi in HXH were Aspergillus, Monascus and Saccharomycopsis, while those in HRA and QCU were Aspergillus and Saccharomycopsis. HXH had the highest moisture content, acidity and starch content, followed by HRA, and the lowest level for QCU. HRA had the highest saccharification and fermentation power, followed by QCU and the lowest level for HXH. Esterification power was the highest in QCU, followed by HRA, and the lowest in HXH. Totally 155, 115 and 113 volatile substances were detected in HXH, HRA and QCU, respectively, the major ones being esters, alcohols, aldehydes, ketones, and pyrazines. The highest contents of alcohols and ketones were found in HXH, the highest contents of alcohols and aldehydes in HRA, and the highest content of pyrazines in QCU. The abundance of Monascus was significantly positively correlated with acidity and the contents of moisture, starch, esters, acids, aldehydes and ketones (P < 0.05); the abundance of Saccharomycopsis was positively correlated with esterification power and pyrazine content; the abundance of Aspergillus was positively correlated with fermentation power, saccharification power and alcohol content. The results of this study have theoretical significance and practical value for improving the quality evaluation system of Daqu quality.