## 2 Results and Discussion
### Volatile Compounds  
A total of 81 aromatic compounds (Table 3) were detected in these wines, among them 16 volatile compounds (highlighted in bold font) which exhibited an important contribution to the overall aroma of the wine due to their concentration being higher than the threshold (Odor activity values (OAV) above 1.0). Esters are secondary metabolites from yeast, synthesized via higher alcohols and acetyl-CoA metabolism [20; 21]. They constituted the largest group of volatiles, and contribute the fruity and flowery characters of wine aroma [20]. In this study, in all 33 esters were detected. After the fermentation, most of the esters showed higher concentrations in the treated wine compared with the control (\(p\leq 0.05\)). Only a few of them were higher in the control than in the treated wine, but their contents were all below the threshold. Ethyl acetate, ethyl butanoate, isoamyl acetate, ethyl texanoate, ethyl octanoate, isoamyl lactate, ethyl decanoate, and ethyl dihydrocinnamate exhibited a content above the threshold (OAV > 1.0) and showed a higher content in the treated wine, which implied an improved fruity aroma could be obtained after freeze concentration. Higher alcohols, also called fused alcohols, are produced by yeast during alcoholic fermentation [22], and usually have a strong and pungent smell, as well as taste. Total higher alcohols in the samples were all in the acceptable range 400-1400 mg/L for red wines [23]. However, the content was significantly higher in the treated wine than the control (\(p\leq 0.05\)) as a consequence of the high ethanol content and high level of pomace to juice ratio, in agreement with [PERSON] and [PERSON]. [PERSON] and [PERSON] found ethanol concentration and solids content could affect the higher alcohols concentration in the final product [24]. 1-Propanol, isobutanol, 1-butanol, isopentanol, and 1-hexanol were the dominant higher alcohols in these wines, and also showed higher content in the treated wine. However, only isopentanol and 1-hexanol showed higher concentrations than the threshold (OAV > 1.0); these two higher alcohols contribute solvent and herbaceous notes for wine, respectively. The OAV of 2-phenylethanol was also above 1.0. Unlike other aliphatic alcohols, 2-phenylethanol is an aromatic alcohol and contributes to rose or honey characters [25]. However, in our study, freeze concentration technology showed a negative influence on this compound. The reason why the treated wine showed a lower amount of 2-phenylethanol is not clear, and further studies are needed. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Physicochemical Index**} & \multicolumn{2}{c}{**Fermentation**} & \multicolumn{2}{c}{**One-Year Aging**} \\ \cline{2-5}  & **Control** & **Freeze Concentration** & **Control** & **Freeze Concentration** \\ \hline Alcohol (\%, \(v\)/\(v\)) & 13.32 \(\pm\) 0.14 b & 14.41 \(\pm\) 0.18 a & 13.12 \(\pm\) 0.16 b & 14.40 \(\pm\) 0.16 a \\ Reducing sugar (g/L) & 2.00 \(\pm\) 0.14 a & 1.45 \(\pm\) 0.07 b & 2.00 \(\pm\) 0.14 a & 2.35 \(\pm\) 0.21 a \\ Total acid (g/L) & 6.30 \(\pm\) 0.28 a b & 6.65 \(\pm\) 0.35 a & 6.00 \(\pm\) 0.28 a b & 5.85 \(\pm\) 0.21 b \\ Volatile acid (g/L) & 0.57 \(\pm\) 0.02 b & 0.55 \(\pm\) 0.03 b & 0.69 \(\pm\) 0.03 a & 0.71 \(\pm\) 0.04 a \\ pH & 3.82 \(\pm\) 0.17 a & 4.07 \(\pm\) 0.18 a & 3.97 \(\pm\) 0.16 a & 4.14 \(\pm\) 0.16 a \\ Glycerol (g/L) & 8.60 \(\pm\) 0.28 b c & 9.60 \(\pm\) 0.28 a & 8.00 \(\pm\) 0.28 c & 9.20 \(\pm\) 0.28 a b \\ \hline \hline \end{tabular} Data are mean \(\pm\) standard deviation of duplicate tests. Different letters in the same category indicate significant differences at \(p\leq 0.05\).  
\end{table} 
Table 2: Physicochemical properties of wines after fermentation and one-year aging. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Acoustic Compound** & **Threshold** & **Odor Description** & **Ref.