Browsing by Author "De Beer, Petrus Johannes"

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    Grape and wine phenolic composition as a result of training system and canopy modification in Vitis vinifera L.cv Shiraz.
    (Stellenbosch : Stellenbosch University, 2015-12) De Beer, Petrus Johannes; Du Toit, Wessel J.; Strever, Albert; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: Non-volatile phenols, such as anthocyanins and tannins, are important parameters used in measuring the quality of red wine, as they are the main components influencing red wine colour and astringency. The Smart-Dyson (SD) training system, as developed by Dr Richard Smart and John Dyson, has previously been investigated as an alternative to the vertical shoot positioning (VSP) training system for vigorous vines, 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 treatment differences influence the wine, have been investigated in international studies, but limited studies have been done under South African conditions. The first aim of this study was to assess differences in the non-volatile phenol composition of Shiraz grapes at harvest originating from a Reduced, VSP or SD training system and to assess whether these differences are reflected in the wines between treatments. Between these selected treatments it was found through spectrophotometer and HPLC analysis that the SD system may sometimes lead to a lower concentration of phenols in wine, although the physical structure of the SD system is expected to be more conducive to a better microclimate to enhance the phenolic concentration. The reduced treatment was also added, as it is a method for reducing vegetative growth by physically removing vegetative matter from the plant. 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 VSP treatments in wine were affected by ageing. The reaction rates of the different non-volatile phenols differ and thus their interaction during wine ageing might differ. This will affect the ageing potential, depending on the relative concentrations of the different phenols. However, the relative differences between the treatments remained unchanged during ageing. The final aim of this study was to look at whether the treatment differences in the wine could be perceived sensorially. As sensory perception is ultimately the main parameter by which wine quality is judged by the consumer, it is important to know if analytical differences are reflected sensorially. When the 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-volatile phenols between the, Reduced canopy treatment and SD- and the VSP training system treatments. It still has to be investigated how management practices relating to these training systems can affect these differences.