Determination of the phenol composition of South African red grapes and wines and the application there of in optimum production of quality wines

Project Number
WW 08-25

Project title
Determination of the phenol composition of South African red grapes and wines and the application there of in optimum production of quality wines

Project leader
Minnaar, P P

Team members
Marais, J
Oberholster, A
Louw, A
October, F

Project description
A lack of knowledge exists on the phenol composition of local red grapes and wine and on the impact these colour and taste compounds have on wine quality. This knowledge is essential in the optimisation of viticultural and enological techniques to produce optimal quality wines. One of the main goals of this project, i.e. to determine the phenol composition of a spectrum of red grapes and wines, has already been realised in part by the analyses of Pinotage, Shiraz and Cabernet Sauvignon wines from the 2002 season. Wines were sampled from the Young Wine and Veritas wine shows according to cultivation distribution in wine producing areas. A liquid chromatographic technique, that is able to determine 38 individual phenols per wine, has been implemented for the analysis of these wines. Interesting cultivar differences have been noted in the levels of certain phenols. The levels of caffeic acid and its tartaric acid derivative, caftaric acid, are significantly higher in Pinotage compared to Shiraz and Cabernet Sauvignon. Notably higher levels of total analysed flavonols were observed in Shiraz compared to the other two cultivars. These findings agree with those from the 2001 season, but need to be verified further by the analysis of more wines and also grapes over a number of seasons to determine possible seasonal effects. Cultivar differences in phenol composition can be used in identifying colour and taste impact phenolic compounds. Identification of such compounds will be an important tool in realising another main goal of this project, i.e. to apply the knowledge obtained from the phenol composition determination in optimising viticultural and enological techniques to produce wines of high quality. In so doing technology will be developed which can improve South Africa’s competitiveness on the international markets. This is true especially seen in the light that the local wine production pattern is turning from white to red wine. The ratios of the main anthocyanins relative to one another in wines are increasingly being used as a measure of wine authenticity. These ratios were determined for the analyses wines from the 2002 season. The data indicate slight distinctions between Pinotage, Shiraz, and Cabernet Sauvignon wines based on these ratios. These data could be of value in setting a standard of characteristic anthocyanin ratios in South African wines.

Article
Rossouw, M, Marais, J. 2003. Phenolic compounds in South African red wines: A preliminary study, WineLand, Mnth Feb (p. 77-79)

Rossouw, M, Marais, J. 2004. The phenolic composition of South African Pinotage, Shiraz and Cabernet Sauvignon wines, South African Journal of Enology and Viticulture, v. 25 (2) (p. 94-104)

FinalReport.pdf

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