Afternoon shading delays ripening and modifies grape flavonoids and wine composition under natural heat stress in semi-arid regions.

To mitigate the rapid ripening by afternoon high temperature in semi-arid wine regions, grapevine artificial shading was applied in a three-year experiment (2021-2023) in China. The moderate shading (1.5 h, MD) and strong shading (2.5 h, SD) were applied in the afternoon. Climatic parameters were collected, grape and wine flavonoids were determined by HPLC-MS. Results revealed that shading reduced the berry surface temperature by up to 4 °C and delayed sugar accumulation, resulting in grapes with higher acidity (∼1 g/L) and lower Brix (∼0.5 °Brix) at harvest. MD and SD wines had lower flavonols, red hue, and anthocyanin derivates. Specific non-methylated anthocyanins and kaempferol-based flavonols were bioindicators of solar radiation. Wine flavor and aging chemistry were also investigated. Overall, afternoon shading delays grape ripening and regulates grape flavonoid profiles and thus modifies wine appearance and flavor. This study provides insights into regulating grape and wine quality in semi-arid regions.