Masters Degrees (Viticulture and Oenology)

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Browsing Masters Degrees (Viticulture and Oenology) by browse.metadata.advisor "Carey, Victoria Anne"

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    Site and vintage response of malic and tartaric acid in Vitis vinifera L. cv’s Cabernet Sauvignon and Sauvignon blanc
    (Stellenbosch : Stellenbosch University, 2013-12) Coetzee, Zelmari; Strever, Albert Erasmus; Carey, Victoria Anne; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: Acids are one of the major components that originate largely from the berry, that are found in wine, and that influence the sensory perception. The presence of organic acids in adequate concentrations in the grape berry, of which tartaric- and malic acid are the main organic acids present, is important as this determines the potential of a must to produce a good and stable wine. The effect of temperature on the organic acid content of the must is widely discussed with higher temperatures in general being associated with lower quantities of organic acids present in the juice, and lower temperatures during ripening associated with higher quantities, specifically in the case of malic acid. Due to the topographical diversity of the Stellenbosch Wine of Origin district and the closeness of the ocean and the occurrence of sea breezes, the mesoclimate differs greatly over short distances. Sixteen sites, consisting of eight Sauvignon Blanc and Cabernet Sauvignon sites respectively, were selected from a broader terroir study site network. Three vintages with complete climatic datasets were selected for vintage comparisons. Climate in the study area was monitored on differing scales, and data from a weather station network, as well as from mesoclimatic dataloggers within the sites were available. The available data was firstly compared to determine the variability of the data, not only between the two climatic scales, but also between the sites. Different climate classification indices and parameters available in literature were thereafter compared and evaluated for the best representation in this area. The Huglin index was found to be a better representation regarding the thermal climatic indices. Due to the great differences between temperatures noted for the mesoclimatic loggers and the nearest automatic weather station, the use of mesoclimatic logger data was preferred, and is advised in future studies where this scale of data is available. Malic and tartaric acid has a definite synthesis period up until véraison, after which the content of tartaric acid remains constant in the berry and the content of malic acid decreases until harvest due to mainly respiration. The temperature data was therefore separated in a synthesis period from flowering to véraison, and a ripening period from véraison to harvest. In this study, clear differences were firstly seen in the climate as expected, not only between sites per vintage, but in addition between vintages and between vintages per site. The phenological differences between the sites could be largely attributed to the differences in temperature as phenology and temperature was found to be highly correlated in this study. Differences in the ripening parameters were noticed in addition to the contents of the organic acids between sites, although no definite contribution of temperature was shown to affect the contents of these compounds at either véraison or harvest. These differences may be attributed to other factors such as the soil water content and the canopy architecture. In addition, these factors all contribute in differing percentages to the differences found in the contents per site. It was found though that temperature can be used as an indicator of the organic acid content in the grape berry, considering that the temperature data is available on a mesoclimatic scale, separated in a synthesis and period of degradation, and the number of hours within the temperature thresholds are determined. Differences seen in the organic acid contents can however not only be attributed to the differences in topography and the temperature as discussed in this study.