## 5 Conclusions  
The temporal profile of the microbial community and volatile compounds during the third round of fermentation of sauce-flavor _baijiu_ in the Beijing region were studied. The results showed that _Lactobacillus_, _Virgibacillus_, _Oceanobacillus_, _Kroppenstedtia_, _unclassified_c_Bacillus_, _Bacillus_, and _unclassified_f_Bacillaceae_ were the core bacterial flora, and _Byssochlamys_, _Issatchenka_, _Monscus_, _Thermoascus_, _Aspergillus_, _Thermoascus_, _Aspergillus_, _Thermo_, _Leitochem_, _Saccharomyces_, and _Pichia_ were the core fungal flora. The acidity of fermented grains drove the microbial community succession. A total of 81 volatile compounds were identified in the 18 samples, among which esters and alcohols were abundant, and their concentrations increased with time. The differences in the profile of flavor compounds and microbial community structure in fermented grains from different rounds in the Beijing region were smaller than those in the fermented grains from the Beijing and Guizhou regions. The difference in microbial community composition and their resulted differences in fermentation parameters of fermented grains were found to be responsible for the differences in the profiles of flavor compounds between sauce-flavor _baijiu_ produced in the Beijing and Guizhou regions.  
**Supplementary Materials:** The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/foods13050670/s1](https://www.mdpi.com/article/10.3390/foods13050670/s1)]([https://www.mdpi.com/article/10.3390/foods13050670/s1](https://www.mdpi.com/article/10.3390/foods13050670/s1)). Figure S1. Rarefaction curves of bacterial Chaol index (A) and Shannon index (B). Figure S2. Rarefaction curves of fungal Chaol index (A) and Shannon index (B). Figure S3. The seven rounds of the manufacturing process of the sauce-flavor _baijiu_. Table S1. Shannon and Chaol indexes for the bacterial community. Groups with different letters mean significant differences (\(p<0.05\)) as determined by one-way ANOVA [PERSON]'s post hoc test. Table S2. Shannon and Chao 1 indexes for fungal community. Groups with different letters mean significant differences (\(p<0.05\)) as determined by one-way ANOVA [PERSON]'s post hoc test. Table S3. Temporal profile of volatile compounds in fermented grains of the third round of fermentation (\(\mathrm{ug}/\mathrm{g}\)). Table S4. Changes of fermentation parameters in the upper, middle, and lower layers of fermented grains. Groups with different letters mean significant differences (\(p<0.05\)) as determined by one-way ANOVA [PERSON]'s post hoc test.  
Figure 7: A summary map of dominant microorganisms and potential functions.  
**Author Contributions:** W.L. and H.Z.: data curation, writing--original draft preparation. H.Z., W.L., R.W. and C.Z.: editing, preparation of figures and tables. X.L.: conceptualization and supervision. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the National Natural Science Foundation of China (no. 31830069) and the Beijing Municipal Natural Science Foundation and Beijing Municipal Education Commission (no. KZ202110011016).  
**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/Supplementary Materials. Further inquiries can be directed to the corresponding author.  
**Acknowledgments:** The authors wish to express their deep gratitude and appreciation for the support obtained from the National Natural Science Foundation of China (no. 31830069) and the Beijing Municipal Natural Science Foundation and Beijing Municipal Education Commission (no. KZ202110011016).  
**Conflicts of Interest:** The authors have no relevant conflicts of interest to disclose.