Leaf removal and wine composition of Vitis vinifera L. cv. Nero d'Avola: the volatile aroma constituents

Background: Defoliation is a cultural practice for crop management in grapevines and the benefits effects have been demonstrated. Here, the influence of 'early' leaf removal on the quality of Nero d'Avola wines was evaluated. Particular attention has been given to the volatile constituents responsible for the wine aroma but also to the total amount of polyphenolic compounds, anthocyanins and flavonoids.

Results: 'Early' defoliation was manually applied and compared with non-defoliated controls. The grapes were harvested at two different ripening times following their technological and phenolic maturity. Statistical quantitative differences occurred among the samples from the four trials (defoliated and control samples, both at two ripening times). Both the time of harvest and the vine leaf removal determined variation in the wine composition. A large number of volatile constituents were identified and quantified; the odour activity values (OAVs) were calculated. Basal leaf removal reduced pH and increased titratable acidity, total amount of anthocyanins, flavonoids, polyphenols and colour intensity in the wines from the first harvest. Results showed the increase of fermentation and varietal aromas in the defoliated wines from the first harvest. Limited differences occurred between the wines from defoliated and control vines relative to the second harvest. Principal components analysis, which was applied to compounds with OAVs ≥ 0.5, allowed the different compounds to be distinguished.

Conclusion: 'Early' leaf removal can lead to a positive effect on the quality of Nero d'Avola under the environmental conditions in which the present study was undertaken but particular attention has to be given to the time of grape harvest. The results also demonstrate that 'early' defoliation can be applied to improve wine quality in the Mediterranean region, where there is a concentration of rainfall during winter, and nearly arid conditions and high temperatures during the summer.