## 3 Results and Discussion  
### Classification of Wines by Geographical Origin and Vintage Based on Oenological Parameters  
Oenological parameters, such as alcohol content, titratable acidity, pH, total phenols, total anthocyanins, and total tannin, are essential parameters for red wine quality [3; 26; 27; 28]. Differences in oenological parameters (alcohol content, titratable acidity, pH, total phenols, total anthocyanins, and total tannin) between the six sub-regions of Ningxia were explored by ANOVA; rarely significant differences were found (Table 1). (12.93% \(v/v\)). The total acidity of Ningxia (5.81 g/L) wine was significantly lower than that of Bordeaux (7.29 g/L). The total anthocyanin content of California (0.20 g/L) and Ningxia (0.17 g/L) wines was significantly higher than that of Bordeaux (0.09 g/L). Since the ethanol content of wine depends on the sugar concentration in the fermentation, wines from warm, dry regions tend to have higher ethanol concentrations than those from cool, wet regions [29]. The high alcohol and anthocyanin content of Ningxia wines appears to be related to the inland location of the Helan Mountains, which have a typical temperate, semi-arid continental monsoon climate. The eastern foothills have a large day/night temperature difference, high annual sunshine hours, and a short monsoon season, which promote the accumulation of high sugar and anthocyanin contents in the grapes. The large day/night temperature difference results in the rapid accumulation of sugar and low acidity. The Ningxia climate, therefore, produces wines with high alcohol and anthocyanin content but low acidity. California (known as the Sunshine Coast) has very high annual sunshine hours, so the wine anthocyanin content is higher than that of Ningxia. There was no significant difference in pH, total phenols, or total tannins between the three regions (Table 1). Differences in oenological parameters between the six Ningxia vintages (2013, 2014, 2015, 2016, 2017, and 2018) were explored (Table 2). Alcohol and anthocyanin content followed an overall downward trend as aging time increased. The alcohol content of the recent vintages, from 2016 (13.93% \(v/v\)), 2017 (13.87% \(v/v\)), and 2018 (13.93% \(v/v\)) was significantly higher than that from 2013 (12.92% \(v/v\)). One explanation for this could be that a warmer climate increases the alcohol content of wines from a given region [30; 31]. Climate change has resulted in a global temperature rise, which promotes an increased accumulation of sugar. The weather records for Ningxia, from March to September 2013-2018 (Table S4 and Figure 2), show that the average temperature and precipitation have been increasing over this period, except for a decrease in 2017. Another explanation for decreased alcohol content in older vintages could be volatility and chemical reactions such as oxidation and esterification, during the aging process. The anthocyanin content of the near vintage wine of 2018(0.24 g/L) was significantly higher than that of the long-aged wine of 2013 (0.05 g/L), 2014(0.08 g/L), 2015 (0.13 g/L), and 2016 (0.15 g/L). This may be due to the polymerization and precipitation during wine aging. The anthocyanin content of the recent 2018 vintage (0.24 g/L) was markedly higher than that of the older vintages from 2013 (0.05 g/L), 2014 (0.08 g/L), 2015 (0.13 g/L), and 2016 (0.15 g/L). Anthocyanins may undergo chemical reactions, such as cyclization, oxidation, and polymerization, to form various anthocyanin derivatives, resulting in decreased anthocyanin content [32].