Effect of fruit zone leaf removal on total glycoconjugates and conjugate fraction concentration of Riesling and Chardonnay (Vitis vinifera L.) grapes

Grape glycosides are, in part, important aroma and flavor precursors. Their quantification may offer a means of determining the impact of viticultural practices, such as leaf removal, on potential wine quality. Fruit zone leaf removal of Riesling and Chardonnay grapevines grown at two sites for two seasons was evaluated for its influence on total and phenol-free grape glycosides at harvest. Vines were trained to a low bilateral cordon system at one vineyard and a high bilateral cordon at the other. The concentrations of total and phenol-free glycosides were higher in Riesling and Chardonnay fruit from leaf-pulled vs control vines at three of four harvest dates. Phenol-free glycosides averaged 80% of the total in Riesling juice and 66% of the total in Chardonnay. Grapevine canopy microclimate plays an important role in determining fruit composition, although knowledge about the relationship between microclimate and aroma/flavor development is limited. This study illustrates the affect of microclimate manipulation on grape glycosides, important components of fruit quality.