Water stress increased polyphenolic quality in 'Merlot' grapes

The interaction between grapevines and their environment is important in determining fruit quality. The effect of water stress was recently examined as a tool to improve grape quality via its effect on polyphenols in 'Merlot' fruit. The study was conducted in the field during 2002 in north-eastern Italy. A 10-year-old vineyard of Merlot, clone R18 grafted onto SO4 and planted on a loamy soil with 15% gravel was used. Water stress was imposed from veraison onwards by maintaining vines at a stem water potential of -1.4 MPa. Compared to the controls the water stress treatment reduced vegetative and berry growth. Sugars were increased and total polyphenols, anthocyanins and catechin concentrations were higher at fruit maturity in the stressed treatment compared to the control. Proanthocyanidins were higher in the skins of stressed berries, but water stress had no effect on its concentration in the seeds. Wines from water stressed fruit had a better aroma, more astringency, a more intense and more brilliant color, and greater harmony in structure than the control wines. The method of extracting polyphenols was extremely important to correctly define the concentration of total and extractable polyphenols. Two different methods of extraction (with ethanol and with acidified methanol) gave a better picture of the effects of water stress on 'Merlot' fruit. Water stress proved to be beneficial on improving the quality of 'Merlot' grapes and wine.