Delaying wine grape ripening by trimming

Abstract

A number of cultural techniques have been proposed in order to delay wine grape ripening in the face of global warming. This study is aimed at evaluating the effects of trimming on delaying berry ripening as well as at the determination of the optimal moment and intensity to realize this cultural practice. The preliminary study was conducted in two experimental vineyards located in Logroño, La Rioja, Spain. In one of them (V1), the intensity of trimming was investigated with 3 treatments carried out: Control (C), Trimming (T) and Double Trimming (DT) In the other one (V2), trimming was done in two different moments: Before flowering (TBF) and after fruit set (TAF). For each treatment, veraison date was recorded, as well as the initial total soluble solids (TSS, oBrix); TSS and anthocyanins were determined weekly in the period of maturation. The grapes were harvested at the same level of TSS and parameters of must were analyzed. In both vineyards, the trimming practice delayed the veraison date significantly, especially the 90%-veraison date. In V1, trimming led to an increase in total acidity and tartaric acid, and a decrease in leaf-fruit ratio, pH and malic acid. No significant difference in anthocyanin content was observed between the treatments, although must from DT and T groups had less concentration compared with group C. Ripening was delayed evidently but the objective of restoring anthocyanin: sugar ratio was not achieved, probably due to the abnormal climate of this vintage. In V2, TBF did not delay the ripening; In contrast, it helped to accelerate the accumulation of sugar during the maturity period. This preliminary year’s results indicate that the ideal moment for trimming is after the fruit set; the optimal intensity of trimming is still not clear, more complementary experiments should be conducted over the next few years.