Interaction of water deficit, canopy modification and ripening : effect on the phenolic and colour composition of Shiraz grapes & subsequent wine

[摘要] ENGLISH ABSTRACT: Phenolic compounds are important quality indicators of a red wine, as they can contribute to thecolour of a young red wine, colour stability during ageing as well as astringency, bitterness,body and overall mouthfeel properties. Wine composition is commonly influenced bywinemaking and viticultural practices.In South Africa it often happens that vines are excessively vigorous, resulting in canopiesthat are too dense, which in turn could have a negative effect on the quantity and quality of thegrapes produced. Viticultural practices such as judicious canopy management and irrigation aredesigned to control vine vigour and yield, thus improving fruit ripening and colour development.Artificial shading and water deficit have been reported to have an influence on the sensoryproperties of red wine as well as on the flavonoid composition. These effects are dependent ona number of factors, however, including the season, cultivar, light intensity, and the extent andtiming of water deficit.There is limited research on the possible interactive effects of grapevine water deficits andcanopy manipulation on grape and wine flavonoid composition in Shiraz, as well as therelationships between berry and wine composition. We thus investigated the effect of canopyreduction in combination with water deficit on the phenolic and colour composition of Shirazgrapes at different levels of ripeness, and in their corresponding wines after alcoholic andmalolactic fermentation as well as after six months' ageing. This study found that it is possible toimprove the phenolic composition of grapes and wine by shoot removal, and some of thetendencies in the wines were also observed after the ageing period. If the shoot removal is notperformed at a very early stage, sunburn damage can occur and this will result in berries with alower mass and volume at harvest due to excessive exposure without the berry having adaptedto the imposed conditions.Harvesting at different ripeness levels also affected the chemical and phenolic compositionof the grapes and resulting wines. The water deficit effect on most phenolic parametersmeasured in the grapes and wine was not as prominent as that of the canopy manipulationtreatment.This study improved our understanding of how an improvement in the canopy microclimateof Shiraz could be reflected in the phenolic composition of wines, along with a potentiallyimportant effect of harvesting date. On this basis it may be possible to attain a specific winestyle. Harvesting at a ripe stage, for example, could result in the production of wines with highercolour density and astringency, while unripe grapes could result in wines with higher levels ofperceivable fresh berry attributes. In particular, canopy reduction could increase the astringencyand body of wines made from grapes subjected to water deficit.

[发布机构] Stellenbosch University