Browsing by Author "Van Rooyen, Rianco"
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- ItemRole of varietal thiols in South African Colombard wines(Stellenbosch : Stellenbosch University, 2019-04) Van Rooyen, Rianco; Du Toit, Wessel J.; Brand, Jeanne; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology.ENGLISH ABSTRACT: Colombard is the second most planted wine grape in South Africa and research that provides insight into and additional knowledge on Colombard may prove particularly useful in the production of quality wine from this cultivar. One of the most important quality drivers is wine aroma. The aroma of a wine may be studied through the quantification of certain compounds, as well as through sensory analysis. There are limited studies that have focused on quantifying the compounds responsible for the aroma of Colombard wine. Varietal thiols are sulphur-containing compounds and include 3-mercaptohexan-1-ol (3MH), 3-mercaptohexyl acetate (3MHA) and 4-mercapto-4-methylpentan-2-one (4MMP). These varietal thiols are normally present at extremely low levels in wine and have been known to contribute to the aromas of ‘passion fruit’, ‘guava’ and other ‘fruity aromas’ in Sauvignon Blanc and Chenin Blanc wines. The aims of this research were to determine whether certain viticultural and oenological practices may influence varietal thiol levels in Colombard wine and to explore the sensory contribution of varietal thiols to the aroma of South African Colombard wine. The effects of different vineyards, yeast strains and juice treatments on varietal thiols levels in Colombard wine were investigated. A classification of commercial wines in terms of the effect of different winemaking practices on varietal thiol levels was also undertaken. The sensory contribution of varietal thiols to the aroma of Colombard wines was also assessed. The origin of the grapes, as well as the choice of yeast strain, significantly influenced 3MH levels, while the latter also had a significant effect on 3MHA levels. Certain juice treatments were found to lead to large increases in 3MH and 3MHA levels. Varietal thiols in commercial Colombard wines were comparable to those reported in young South African Sauvignon Blanc and Chenin Blanc wines. Significant differences in varietal thiol levels were found for the origin of the grapes (3MH), vineyard yield (4MMP), method of juice clarification (3MH), and the bulk price point of the wine (3MH and 3MHA). Varietal thiols seem to play an important role in the ‘guava’ and ‘passion fruit’ aromas in South African Colombard wines. The results of this research have made a contribution to the sensorial characterisation of Colombard wines. With this new knowledge, viticultural and oenological decisions may be adapted to produce market-specific Colombard wines.