## 2 Results and Discussion
### Sensory Evaluation  
To further confirm the sensory feature differences that the freeze concentration process might bring to the wine, sensory evaluation of the two wines after the fermentation and the aging process, respectively, was carried out (Figure 1).  
After fermentation, the treated wine showed a better sensory profile (Figure 1a). The obvious improvement was mainly highlighted in the appearance and mouthfeel, especially the structure and aftertaste properties. It has been confirmed that both the structure and the aftertaste of wine are mainly related to the composition and distribution of non-anthocyanin phenolic compounds [42; 48]. In the present study, the freeze concentration treatment significantly changed the composition of flavan-3-ols and phenolic acids, which might result in such an alteration to the treated wine (Table 4). In addition, the improvement of the appearance in the treated wine could be mainly related to the higher level of anthocyanins, especially non-acylated anthocyanins (Table 4), since anthocyanins are the important contributor for wine color [57; 58].  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Color Attribute**} & \multicolumn{2}{c}{**Fermentation**} & \multicolumn{2}{c}{**One-Year Aging**} \\ \cline{2-5}  & **Control** & **Freeze Concentration** & **Control** & **Freeze Concentration** \\ \hline L* & 65.52 \(\pm\) 3.70 a & 52.37 \(\pm\) 3.05 b & 61.61 \(\pm\) 3.93 a & 62.64 \(\pm\) 3.83 a \\ a* & 37.3 \(\pm\) 2.09 b c & 49.37 \(\pm\) 3.10 a & 32.69 \(\pm\) 1.72 c & 36.98 \(\pm\) 2.19 b c \\ b* & 5.97 \(\pm\) 0.47 c & 3.61 \(\pm\) 0.20 d & 19.32 \(\pm\) 1.44 a & 13.40 \(\pm\) 0.97 b \\ C* & 37.78 \(\pm\) 0.22 b & 49.51 \(\pm\) 0.11 a & 37.97 \(\pm\) 0.04 b & 39.34 \(\pm\) 0.19 b \\ H & 9.10 \(\pm\) 0.67 c & 4.18 \(\pm\) 0.16 d & 30.59 \(\pm\) 0.88 a & 19.91 \(\pm\) 0.15 b \\ \hline \hline \end{tabular}  
* Data are mean \(\pm\) standard deviation of duplicate tests. Different letters in the same row indicated significant differences at \(p\leq 0.05\).  
\end{table}
Table 6: Color attributes of wine after fermentation and one-year aging.  
The fragrance also showed an improvement in the treated wine. As the results by GC-MS showed, the freeze concentration increased the contents of esters while it decreased the amount of volatile acids (\(p\leq 0.05\)), which makes it a good way to improve wine aroma. It should be mentioned that although the treatment increased the contents of higher alcohols, it did not show a significant negative effect on wine aroma, which may be because the increased higher alcohols were still within the acceptable range as reported [23].  
All things taken into consideration, the treated wine showed a better fragrance than the control according to the sensory panel (Figure 1a). Except for the composition of aromatic compounds, other factors could also play important roles in wine aroma [59]. For example, it has been reported that the synergistic effect from the low OAV value volatile compounds could improve the overall aroma of wine [34]. Similarly, the matrix effect of non-volatiles has been also reported to impact the wine aroma expression [7]. In the present study, glycerol had a higher content in the treated wine, which might enhance thje matrix effects. Differences in the sensory attributes of these wines after a one-year aging period were still observed (Figure 1b). For example, a significant improvement in the appearance of the treated wine still existed, which resulted mainly from the higher content of anthocyanins in the treated wine compared to the control. The scores on mouthfeel and fragrance properties decreased after the aging process, but fortunately the treated wine performed better than the control.