• Addresses “high sugar-low acid” imbalance in wines under climate warming. • Grape stem addition modulates wine phenolics, color, aroma, and antioxidant activity. • Optimal stem ratios (1/8–1/2) are established for 'Cabernet Sauvignon' and 'Marselan'. • Delayed harvesting boosts phenolic content and alters volatile profiles in stems. • Provides a sustainable, waste-to-resource strategy for quality regulation. Due to climatic variability, wine grapes often fail to reach optimal maturity within the typical harvest window. In arid and semi-arid regions of northwestern China, grape quality exhibits significant imbalances analog associated with harvest timing. In production practice, it was serendipitously observed that grape stems, which are waste from the grape industry, can effectively solve problems such as "high sugar content and low acidity". This study evaluated the use of grape stems as a targeted regulation tool for improving ordinary table wine quality under specific high sugar-low acidity conditions. The results showed that as a potential quality regulation tool, the chemical composition, phenolic and volatile substance contents of grape stems are significantly affected by the harvesting period. Results showed that delayed harvesting increased total phenolic content in stems by 15%–30% and altered volatile profiles, reducing green notes. Wine with stems (1/8–1/2 proportion) exhibited decreased ethanol (by 0.5%–1.2% v/v) and total acid (by 0.3–0.8 g/L), while pH and TSS increased. TPC rose by 10%–25%, and antioxidant capacity was enhanced by 15%–40%. Color intensity ( a* value) decreased, and sensory evaluation indicated optimal aroma balance and palate richness at 1/8 stem proportion in late‑harvested Ningxia wines. Based on the above indicators, the appropriate grape stem addition amounts for different varieties in the two production areas under different harvesting periods were determined, providing a theoretical basis for optimizing winemaking processes for specific raw material challenges, while acknowledging that destemming remains the standard practice for premium wine production.
Wang et al. (Sun,) studied this question.