Doctoral Degrees (Viticulture and Oenology)

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Browsing Doctoral Degrees (Viticulture and Oenology) by browse.metadata.advisor "De Villiers, Andre J."

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    Microclimate and grape ripeness effects on the phenolic composition of grapes and wine (Vitis vinifera L. cv. Shiraz/101-14 Mgt)
    (Stellenbosch : Stellenbosch University, 2018-12) Minnaar, Phillipus Petrus; Hunter, Jacobus Johannes; De Villiers, Andre J.; Stellenbosch University. Faculty of AgriSciences. Dept. Viticulture & Oenology & Institute for Wine Biotechnology.
    ENGLISH ABSTRACT: The study was aimed at the impact of canopy microclimate by means of grapevine row orientation (GVRO) and grape ripeness levels (GRL) on individual phenolics of Vitis vinifera L. cv. Syrah/101-14 Mgt grapes and wine. Grapes were harvested over four consecutive vintages at ca. 22°Brix, 24°Brix and 26°Brix GRL and representative of NS, EW, NE-SW and NW-SE GVRO. Wines were made from harvested grapes. Phenolics were quantified in lyophilised grape skin and wine samples. Treatment affects were distinguishable by HPLC and sensory analyses and confirmed by ANOVA, PCA and MFA. Grapes from NE-SW GVRO were highest in anthocyanins, flavonols and flavan-3-ols at ca. 22°Brix, whereas those from NW-SE GVRO were highest in anthocyanins, flavonols, flavan-3-ols, and phenolic acids at ca. 24°Brix. At a GRL of ca. 26°Brix, grapes from NW-SE GVRO were highest in flavonols and phenolic acids, whereas anthocyanins were highest from NS GVRO and flavan-3-ols highest from NS and NE-SW GVRO. Lowest anthocyanins and phenolic acids were in grapes from NW-SE GVRO at ca. 22°Brix GRL. Grapes at ca. 24°Brix and 26°Brix GRL from NS GVRO were lowest in flavonols. Flavan-3-ols seemed lowest in grapes from NS and NW-SE GVRO at ca. 24°Brix and 26°Brix GRL, respectively. At GRL of ca. 24°Brix and 26°Brix, lowest anthocyanins and phenolic acids were found for NE-SW GVRO. Wines from NW-SE GVRO had highest anthocyanins at ca. 22°Brix and 24°Brix GRL, but wines at ca. 26°Brix from EW GVRO had highest anthocyanins. Flavonols, flavan-3-ols and phenolic acids were highest in wines from NE-SW GVRO at ca. 22°Brix GRL. At a GRL of ca. 24°Brix and 26°Brix, wines from NS and NW-SE GVRO, respectively, were highest in flavonols, flavan-3-ols and phenolic acids. Lowest anthocyanins, flavonols, flavan-3-ols and phenolic acids were found in wines from EW GVRO at ca. 22°Brix GRL. Phenolic acids were also lowest in wines from EW GVRO at ca. 24°Brix GRL. At ca. 24°Brix GRL, lowest anthocyanins were found in wines from NS GVRO, lowest flavonols from NE-SW GVRO and lowest flavan-3-ols from NW-SE GVRO. At ca. 26°Brix GRL, lowest anthocyanins, flavonols and flavan-3-ols occurred in wines from NS GVRO and lowest phenolic acids from NE-SW GVRO. Phenolics, sensory attributes, GVRO and GRL were associated with each other. Sensory attribute scores of wines differed among GVRO. Wine quality was associated with NE-SW and NW-SE GVRO. Despite the complexity of impacting factors and different phenolics, results showed the likelihood that a chosen GVRO and GRL may affect wine style. Grapevine row orientation enables a “natural” change in canopy microclimate, leading to grape quality improvements. In practice, a desirable GVRO may not necessarily be applicable to all environments. Management of the fruiting zone remains an option for increasing or decreasing grape exposure, irrespective of GVRO. Further research is needed to understand the relationships of vine phenology, light intensity, temperature and GVRO with grape and wine phenolic profiles and wine quality. Phenolic concentration differences in wines in this study and association thereof with GVRO is important in oenology, because phenolics can be affected by vineyard practices, which may further lead to a desired wine style. However, phenolics of grapes and ultimately of wine, are affected by multiple factors, e.g. climate, grape cultivar, viticultural practices, GRL and berry size, all of which must be considered when a specific wine style is intended.