Effects of severe trimming after fruit set on the ripening process and the quality of grapes

Some cultural techniques have been proposed in order to delay ripening of wine grapes under global warming. This study on two varieties in a two year period (2014-2015), was aimed at evaluating the effects of severe trimming after berry set on delaying grape ripening as well as on grape quality. The experiment was carried out for 'Tempranillo' in an experimental vineyard in Logroño (VL, with irrigation) and for 'Grenache' in a commercial vineyard in Badarán (VB, without irrigation). Both places are within DOC Rioja and in each of them three treatments were carried out: control (C), trimming once (T) and trimming twice (TT). In both vineyards, trimming treatments reduced leaf area (LA) to production (P) ratio (LA/P) significantly and delayed the veraison dates. In VL, relative to C, T and TT delayed the harvest dates by 14 to 23 days, obtaining a comparable level of total soluble solids (TSS) and a similar total anthocyanin concentration (TAC). In VB, T delayed the harvest dates by 16 to 20 days without significant differences in TSS and TAC from C. However, grapes of TT failed to mature properly due to the serious shortage of LA. From an acid perspective, trimming treatments were likely to improve organic acid composition by increasing the tartaric acid and reducing the malic acid, as long as the LA/P was not too low. The relatively cooler ripening condition caused by trimming seemed insufficient for a better anthocyanin synthesis.