Investigation of Enological Techniques to Mitigate the Effects of Grapevine Red Blotch Disease on Wine Composition

Background and goals Grapevine red blotch disease (GRBD) causes a delay in ripening events in grapes, subsequently decreasing sugar accumulation, inhibiting anthocyanin biosynthesis, and affecting cell wall metabolism. Phenolic extractability is reduced in wine made from GRBD fruit, which can be slightly improved by extending the ripening period of GRBD grapes. However, further enological techniques that increase phenolic concentrations in wine or facilitate cell wall degradation have not been investigated in GRBD fruit. Methods and key findings Vitis vinifera L. cv. Merlot grapevines with GRBD symptoms were harvested twice, two weeks apart, in 2019 and 2020. Pectolytic enzyme addition and extended maceration were performed on the second harvest of GRBD fruit to improve phenolic extraction during fermentation. Phenolic concentrations, volatile profiles, and sensory characteristics were analyzed for all wine produced. Seasonal factors and harvest time were found to affect the phenolic extractability, chemical composition, and sensory characteristics of wine made with GRBD fruit. Compared to control wine, extended maceration of wine made with GRBD fruit largely did not improve chemical composition or sensory characteristics, and on ly minor increases of tannin concentrations were found during fermentation. Wine composition and sensory properties primarily depended on vintage and harvest time, rather than enological technique applied. Conclusions and significance A delayed harvest of diseased fruit had a greater effect on phenolic composition in the wines than did the analyzed enological techniques, consistent with previous findings. However, this finding depends on variations across different seasons.