Masters Degrees (Institute for Wine Biotechnology)

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Browsing Masters Degrees (Institute for Wine Biotechnology) by Author "Bruwer, Freda Aléta"

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    Effect of foliar Nitrogen and Sulphur spraying on white wine composition ( Vitis vinifera L.cv. Chenin Blanc and Sauvignon Blanc)
    (Stellenbosch : Stellenbosch University, 2018-12) Bruwer, Freda Aléta; Buica, Astrid; Stellenbosch University. Faculty of AgriSciences. Dept. Viticulture & Oenology & Institute for Wine Biotechnology.
    ENGLISH ABSTRACT: Chenin Blanc and Sauvignon Blanc, as the most planted wine cultivars in South Africa, are of great interest to researchers worldwide, due to its increased high wine quality. Wine quality is interlinked with wine aroma. Vine nitrogen fertilization influence the vine physiology and composition of the grapes, and enhanced aroma expression. By addressing Yeast Assimilable Nitrogen (YAN) deficiency with foliar fertilization, during the ripening season, to low nitrogen containing vines, the aroma potential of the wines can be potentially influenced. The main aim of this research study was to assess the influence of different foliar fertilization treatments on Chenin Blanc and Sauvignon Blanc vines planted in various locations in South Africa. For each season, two vineyards with a history of producing low nitrogen content grapes were used, one vineyard per cultivar. The vineyards received sulphur and nitrogen foliar treatments twice before véraison. During winemaking, the juices and wines underwent analysis for non-volatile and volatile content. The wines underwent maturation for three and nine months, and then sensorially and chemically analysed. In Chapter 2 the various wine compounds and classes of compounds present in Chenin Blanc and Sauvignon Blanc wines were analysed. The specific characteristics, aroma composition and its implications on the sensory perception of the cultivars were reviewed. The influence and contribution of different fertilization practices on the chemical compounds and resulting wine’s aromatic expression were investigated. The first part of the research study investigated the effect of foliar fertilization on the non-volatile content in the juices and wines. In Chapter 3, the nitrogen containing foliar fertilization applications increased the YAN levels. This increase is relevant not only for yeast metabolism, but also for the aromatic potential of a wine, as certain amino acids being precursors of aroma compounds. Glutathione were also influenced by the treatments for both years and both cultivars, but the trends were not as evident as with YAN. The second part of the study assessed the effect of various fertilization treatments on the volatile content of the juices and aged wines. Sensory analysis and chemical analysis were used to assess the wines after three and nine months of bottle maturation. Chapter 4 highlighted that sulphur containing foliar treatments influenced the volatile content of major volatiles and volatile thiols. The overall volatile content of the wines was very similar but identified a clear vintage and age effect during maturation. Sensory analysis classified the Chenin Blanc wine with ‘tropical’ and ‘fruity’ aromas, while Sauvignon Blanc wines had prominent ‘tropical’, ‘passion fruit’, and ‘grapefruit’ aromas. During bottle maturation, some notes and aroma characters were maintained but their frequency of citations changed. The results of this research study contributed to the knowledgebase on South African Chenin Blanc and Sauvignon Blanc wines, but also concluded that foliar fertilization can influence the non-volatile and volatile content of wines. South African winemakers and the industry can use this information to make decisions at the viticulture and winemaking level to produce wines with more desirable sensory attributes.