## 4 Discussion  
In this study, three main results were received. First, the concentration of tartaric acid in the wines declined with cold stabilization treatment from 11 days to 15 days, as expected. Second, the wine pH value declined significantly during bottle storage, and cold treatments significantly reduced the pH value of wines compared with the control group after 6 and 12 months of bottle storage. Finally, some main components of ethyl esters and norisoprenoids tend to increase during bottle storage, which is highly correlated to the pH declining. The cold treatment duration for the wines to obtain tartaric stability varies with wines [2]. In 1999, [PERSON] et al. studied the composition of the tartrate precipitates deposited on stainless steel tanks during the cold stabilization of white wines. They found that a complete stabilization of Grenache white wine was achieved within eight days, whereas the Macacbeu white wine had not yet achieved stabilization after six weeks [10]. Researchers compared the effects of cold treatment, ion exchange resins, electrodialysis, potassium polysapartate, and carboxymethyl cellulose on the tartrate stabilization of Monastrell red wines. They concluded that cold treatment for 15 days could effectively keep the tartrate stability of wines even after one year of bottle storage [13]. [PERSON] et al. observed that cold treatment for seven days could impart tartaric stabilization to fino, medium, and cream wines [15]. In our study, no new crystal precipitation in the Riesling dry wines appeared in the cold treatment at \(-5.3\ ^{\circ}\)C for over 13 days. Potassium ion (K\({}^{+}\)) is at higher concentrations in grape juice and the bitartrate (HT\({}^{-}\)) species is usually at higher concentrations than tartrate (T\({}^{2-}\)) at the normal wine pH range (pH 3.0-4.0) [5]. As a result, wine cold stabilization treatment primarily generates potassium bitartrate (KHT) crystals [5]. KHT precipitation is always accompanied by an increase or decrease in wine pH, which highly depends on the pH value prior to precipitation [2], and pH 3. 65 is a key dividing point [5]. That is, tartrate stabilization treatment on wines below pH 3.65 may result in a pH decrease because the wines have a much higher concentration of free tartaric acid (H\({}_{2}\)T) in comparison to its tartrate (T\({}^{2-}\)), and H\({}_{2}\)T/HT\({}^{-}\) equilibrium shifts to increase HT\({}^{-}\) and liberate H\({}^{+}\), which eventually leads to a pH decrease [2]. In contrast, in the wines above pH 3.65, KHT precipitation will result in a pH increase as a higher concentration of T\({}^{2-}\) makes the HT\({}^{-}\)/T\({}^{2-}\) equilibrium shift to increase HT\({}^{-}\) through bounding H\({}^{+}\)[5]. The Riesling wine pH was about 3.16 before the cold treatments in this study. The above tartaric acid chemistry explains why the pH declined with the cold treatment duration and bottle storage. Much research so far has focused on the effect of the cold stabilization treatments such as ion exchange resins, carboxymethylcellulose, potassium polysapartate, and electrodialysis on the phenolic profile and chromatic characteristics [13; 16; 29]. [PERSON] et al. Figure 5: Aroma sensory evaluation scores of the 11-day to 15-day cold treatment wines (T11–T15) and the control wine (T0) at 6 months and 12 months of bottle storage. observed that cation-exchange resin-treated wines had higher concentrations of aromatic compounds such as hexyl acetate, isobutanol, 2-phenylethyll alcohol, ethyl isovalerate, and diethyl succinate after 6 months of bottle storage [4]. Esters are important contributors to wine aroma [30]. During bottle storage, esterification and ester hydrolysis strongly depend on wine pH [31]. Lower pH will accelerate the acid-catalyzed esterification or hydrolysis [31; 32; 33]. Our result also demonstrated this point to some extent.