Effects of cluster thinning on grape composition: Preliminary experiences on 'Sangiovese' grapevines

Effects of cluster thinning on grape and wine quality has been widely explored, but literature results have shown that yield reduction and quality improvement are not always strictly related and may depend from several factors (cultivar, time of application, environmental conDitions). The trial was conducted over a two-year period (2003-2004) on cv. Sangiovese, spur-pruned cordon trained (1 m x 2.8 m spaced) in a hillside vineyard near Bologna. In the first year the vines were adjusted to 15 clusters per plant after fruit set and at veraison the plants were randomly Divided in three groups: a) C, unthinned vines (15 clusters). b) T1, thinned at 10 clusters per vine; c) T2, thinned at 5 clusters per vines. The same treatments were applied in the second year of experiment. The data concerning the ratio between total leaf area and production at 2003 harvest were 1.7, 2.3 and 3.9 m²/kg and 1.1, 1.7 and 3.1 in 2004, for C, T1 and T2 respectively. Soluble solids content of grapes (°Brix) was 21.9, 22.8 and 22 in 2003 and 21.8, 22.7 and 23.2 in 2004 for C, T1 and T2 respectively. In general, berry skin analyses showed a tendency to a decreasing in tri-substituted anthocyanins (delphiniDin-3-glucoside, petuniDin-3-glucoside and malviDin-3-glucoside) and an increasing of Di-substituted anthocyanins (peoniDin-3-glucoside and cyaniDin-3-glucoside) in thinned vines, especially in 2004. Total anthocyanins measured in 2004 were 874, 1192 and 1066 mg/kg in C, T1 and T2. Sensorial analysis of wines obtained from microvinification in 2003 showed no significant Differences between treatments, while a significant effect of thinning was recorded on 2004 wines.