## 3 Results and Discussion  
### Changes in Volatiles during the Fermentation of Yellow Wine  
Yellow wine contains a variety of volatile substances, which are mainly derived from raw materials and the metabolites of microorganisms [30]. In the present study, 36 volatile substances were annotated during the fermentation of yellow wine (Table 2), and all these compounds could be classified into seven groups (Figure 2A), including 13 esters, eight alcohols, four aldehydes, one phenol, one acid, one ketone, one ether, and seven other substances (e.g., alkanes, naphthalene, azoles, nitrogenous compounds). It was found that aldehydes and esters are major of volatile compounds in F0 (Figure 2B). Aldehydes reduced from 36.8% to 1.77% with the progress of fermentation. This phenomenon might be caused by the conversion of aldehydes into alcohols during the fermentation process. Furthermore, some of the aldehydes combined with higher alcohols to form acetals [12]. Esters increased in F2 and F3 but decreased sharply by 22.59% after filtering (F4). Alcohol rose from F0 and maintained high relative content in F2, F3, and F4. The esters kept decreasing, especially after filtering. Previous research has indicated that alcohols are more persistent than esters during the fermentation of yellow wines, and our findings support this [31]. This is said to be because esters are less soluble in water and ethanol, hence esters are lost with the lees during pressing, resulting in a quick decrease in their relative content [12]. As a result, the pressing procedure for yellow wine should be altered to retain more of the wine's essential esters and therefore enhance its flavor. Acids play an important role in the flavor of most fermented foods. In this investigation, the sole acid associated with yellow wine was acetic acid, which began to be generated in F3 and rose to 24.46% in F4. It has been reported that over the duration of 3-5 days of yellow wine fermentation, lactic acid bacteria increased from 2.6 lg to 5.43 lg [32]. This indicates that acids began to accumulate in the yellow wine during this period, as a result of the proliferation of lactic acid bacteria. The study Indicated a considerable variation in the flavor material composition of yellow glutinous rice wine and yellow sorghum wine. After 5 days of fermentation, the sorghum wine was dominated by acids and esters, with a little alcohol. By contrast, glutinous rice wine contains more esters and alcohols, which may make sorghum wine taste thinner than glutinous rice wine [33; 34]. Previous research has also discovered that changing the types of grains and soaking durations changes the amino acid and organic acid content of yellow wine, which influences its flavor [35]. As a result, research into the variations in volatiles across various grains must be expanded in order to improve the categorization of yellow wines. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**NO. **} & \multicolumn{1}{c}{**Compound Name**} & \multicolumn{1}{c}{**Formula**} & \multicolumn{1}{c}{**CAS**} & \multicolumn{1}{c}{**Relative Content (\%)**} & \multicolumn{1}{c}{**F4**} \\ \cline{2-9}  & & & & **F0** & **F1** & **F2** & **F3** & **F4** \\ \hline H1 & Dimethyl Ether & C\({}_{3}\)H\({}_{0}\)O & 115-10-6 & 6.699 \(\pm\) 0.66 b & & 2.00 \(\pm\) 0.05 c & 8.53 \(\pm\) 0.71 a \\ H2 & Nonanal & C\({}_{3}\)H\({}_{8}\)O & 124-19-6 & 25.79 \(\pm\) 2.20 a & 4.2 \(\pm\) 0.10 b & 0.94 \(\pm\) 0.07 c & 0.20 \(\pm\) 0.01 c & 1.48 \(\pm\) 0.09