Grape and wine phenolic composition as a result of training system and canopy modification in Vitis vinifera L.cv Shiraz.

[摘要] ENGLISH ABSTRACT: Non-volatile phenols, such as anthocyanins and tannins, are important parameters used in measuring thequality of red wine, as they are the main components influencing red wine colour and astringency. TheSmart-Dyson (SD) training system, as developed by Dr Richard Smart and John Dyson, has previouslybeen investigated as an alternative to the vertical shoot positioning (VSP) training system for vigorousvines, as it has the effect of bringing the vine 'into balance and has been shown to increase grape yield.The effects of the SD training system on the non-volatile phenols of the grapes, and how these treatmentdifferences influence the wine, have been investigated in international studies, but limited studies havebeen done under South African conditions.The first aim of this study was to assess differences in the non-volatile phenol composition of Shirazgrapes at harvest originating from a Reduced, VSP or SD training system and to assess whether thesedifferences are reflected in the wines between treatments. Between these selected treatments it was foundthrough spectrophotometer and HPLC analysis that the SD system may sometimes lead to a lowerconcentration of phenols in wine, although the physical structure of the SD system is expected to be moreconducive to a better microclimate to enhance the phenolic concentration. The reduced treatment was alsoadded, as it is a method for reducing vegetative growth by physically removing vegetative matter from theplant. This also leads to a better microclimate, but may have a negative effect on the yield.The second aim of the study was to examine how the differences between the reduced, SD- and VSPtreatments in wine were affected by ageing. The reaction rates of the different non-volatile phenols differand thus their interaction during wine ageing might differ. This will affect the ageing potential, dependingon the relative concentrations of the different phenols. However, the relative differences between thetreatments remained unchanged during ageing.The final aim of this study was to look at whether the treatment differences in the wine could beperceived sensorially. As sensory perception is ultimately the main parameter by which wine quality isjudged by the consumer, it is important to know if analytical differences are reflected sensorially. Whenthe wines were tasted, the panel could in general not find an association between the treatments.The results generated from this study show that there were some differences regarding non-volatilephenols between the, Reduced canopy treatment and SD- and the VSP training system treatments. It stillhas to be investigated how management practices relating to these training systems can affect thesedifferences.

[发布机构] Stellenbosch University