Interactive effect of temperature and irrigation on grape composition during berry development in Cabernet Sauvignon

Project Number
WW KB 02

Project title
Interactive effect of temperature and irrigation on grape composition during berry development in Cabernet Sauvignon

Project leader
Myburgh, P

Team members
Van Heerden, A
Myburgh, P
Lambrechts, M G
Oberholster, A
Walters, H
Deloire, A

Project description
Viticultural variables can influence the composition of tannins and anthocyanins and other flavonoids in grapes, but their extractability and stabilisation during winemaking into coloured polymeric pigments has a greater influence on wine colour than concentration alone. The factors which influence firstly extractability of flavonoids and secondly their formation into polymeric pigment are largely unresolved in viticultural and enological research. The proposed study aims to look at three field variables in two Cabernet Sauvignon blocks in different localities: climate, temperature, irrigation and grape maturity levels to produce wines of differing flavonoid composition. The grape and wine samples will vary in one anthocyanin:tannin concentration, together with differences in tannin-anthocyanin interactions and polymerisation during fruit development (i.e. loss of ‘green’ tannins with berry maturity), and in berry skin composition and pigment extractability. The aim of the study is to explore the downstream events of fermentation and bottle ageing on the formation of stable polymeric pigments, as well as factors influencing the production of ‘green tannins’ in Cabernet Sauvignon wine.

Objectives of the proposed project are: To optimise the Sarneckis et al. (2006) and Habertson-Adams methods for the determination of tannin concentration in Cabernet Sauvignon grapes and wines. To produce small-scale wines from grapes sampled from climatically distinct localities with three superimposed irrigation levels within the Swartland area To assess changes in tannin and phenolic composition of grape and wine samples using spectrophotometric methods, with special reference to the development of stable, tannin-bound polymeric pigment a) In grape samples taken at weekly intervals pre- and post-veraison, up to harvest b) In grape samples taken from the different viticultural treatments outlined above c) In finished and aged wine samples produced from grapes in a. and b. d( In musts sampled during fermentation of c. To assess wines sensorially for their astringency, mouth-feel, tannin structure, tannin ‘greenness’ (see Distell 2 application). To draw correlations between data derived to characterise phenolic composition, and sensory attributes of the wines, in terms of tannins.

Presentation(s)
Mehmel, T O. 2010. Effect of climate and soil conditions on Cabernet Sauvignon grapevines in the Swartland region with special reference to sugar loading and anthocyanin biosynthesis. 27 October, University of Stellenbosch, Stellenbosch, South Africa.

Thesis
Mehmel, T O. 2010. Effect of climate and soil water status on Cabernet Sauvignon (Vitis vinifera L.) grapevines in the Swartland region with special reference to sugar loading and anthocyanin biosynthesis. MScAgric (Viticulture and Enology) University of Stellenbosch, Stellenbosch, South Africa.

FinalReport.pdf

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