## 4 Conclusions  
The results demonstrate that the microbial metabolism exhibited significant activity during the pre-fermentation and mid-fermentation stages, which were characterized by a higher water content and the efficient utilization of starch for saccharification. \(\alpha\)-amylase and glucoamylase activities displayed a sharp decline, while acid protease, cellulase activity, and lipase activity showed an increase. Additionally, the acidity gradually increased as the fermentation progressed. The microbial structure of Hunan light-flavor Baijiu at different fermentation periods was investigated using high-throughput sequencing technology. A total of fifty bacterial genera and twenty-two fungal genera were identified in this study. Lactobacillus and Saccharomyces were found to be the predominant microorganisms among bacteria and fungi, respectively. Notably, there were substantial variations in the microbial composition and abundance observed across different fermentation periods, highlighting the complexity of the microbial structure during the fermentation stage. The results of a Spearman correlation analysis of physicochemical indicators with fungal and bacterial microorganisms show that _Lactobacillus_ and _Saccharomyces_ were the dominant genera for bacteria and fungi, respectively, which suggests that these physicochemical indicators drive changes in the flora of _Saccharomyces_ and _Lactobacillus_. At the same time, the growth and metabolism of _Saccharomyces_ and _Lactobacillus_ could also have an important effect on the enzyme activity, ethanol content, and acidity, which are conducive to the formation of the Baijiu flavor. Additionally, a total of 46 volatile flavor compounds were detected via GC-MS in the fermented grains samples, of which esters constituted the major portion, and nine key flavor compounds with an ROAV \(>\) 1 were identified throughout the fermentation process. Isoamyl acetate had the highest ROAV and made the greatest contribution to the flavor, enhancing the floral and fruity aroma of the fermented grains. These results provide a data reference and theoretical guidance for the industrial development of light-flavor Baijiu.  
**Author Contributions:** A.H.: methodology, writing--original draft preparation, writing--reviewing and editing: J.X.: data curation, writing--original draft preparation; T.Z.: investigation, validation; J.H.: software; R.J.: investigation; Y.D.: validation; H.C.: project administration, Z.L.: methodology, supervision, funding acquisition. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the Doctoral Research Start-up Fund of Guiyang University, Micro-ecology of Wine-making and Quality Analysis of the Rounds of Wine in the Core Region of Sauce-type Baijiu (Project No. GYU-KY-[2022]).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author.  
**Conflicts of Interest:** Author [PERSON] was employed by Hunan Guoyuan Liquor Co., Ltd. [PERSON] has contributed toward project administration. The objectivity and authenticity of the experimental results and discussion were not affected by the company. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.