Determination of the optimal ripeness of South African red grapes in terms of their phenol composition

Project Number
WW 08-29

Project title
Determination of the optimal ripeness of South African Shiraz grapes in terms of their phenolic composition/Grape Ripeness and Microclimate Effects on the Phenolic Composition of Grapes and Wine (Vitis vinifera L. cv. Shiraz/101-14 Mgt)

Project description
The objective of the project is to determine the optimal ripeness of South African Shiraz grapes in terms of their phenolic content. A
second objective, which is part of a doctoral degree, is the grape Ripeness and Microclimate Effects on the Phenolic Composition of
Grapes and Wine (Vitis vinifera L.cv. Shiraz/101-14 Mgt). There appears to be a lack of scholarship regarding the changes of individual
phenolic concentrations over ripeness of South African grown Shiraz grapes. It appears that grape ripeness and different row
orientations of canopies effect the phenolic concentrations of Shiraz grapes.

The knowledge of individual grape phenolic compound concentrations over grape ripeness can provide answers to questions such as:
1. At which stage of grape ripening are individual phenolic compound concentrations optimal?
2. Does grape colour correlate with optimal phenolic concentrations?
3. How does the optimal phenolic concentration in the grapes correlate with the phenolic concentrations of wine and with overall wine
quality?

Experimental work was conducted at the ARC’s experimental farm in Robertson, where variables such as rootstock of the vine, clone of the vine, canopy management and general viticultural practices were kept constant. Ambient temperatures, annual rainfall and prevailing wind were monitored. Shiraz grapes were harvested at three different ripeness levels (approx. 22°B, 24°B and 26°B) from four different row orientations from both sides of the canopy over four consecutive vintages (2008, 2009, 2010, 2011). Shiraz grape skins were lyophilized and subjected to chemical extraction prior to chemical analysis. Wines were produced from the corresponding harvested grapes. Twenty-five individual phenolic compounds were quantified in Shiraz grape skin and Shiraz wine samples by means of a liquid chromatographic method. Titratable acidity and pH were also measured in the wine samples. Wines were also subjected to sensory analyses.

The results point to the effect of different treatments, i.e. row orientation/light intensity have on the phenolic compound concentrations of
Shiraz grapes and Shiraz wine. Trends and patterns relating to treatment and phenolic concentrations, including sensory data were evident in the results. The results show that certain treatments (light intensities/row direction) have an effect on the phenolic compound concentration of
Shiraz grapes and wine including sensory attributes.

Phenolic compound concentrations of Shiraz grapes are affected by light interception or light exposure (microclimate/row orientation).
Grapevines planted to a NS and an E-W row orientation are conducive to increased flavanol concentrations. This implicates row orientation, training systems and pruning techniques. The level of light exposure to grapevines planted to a NE-SW and a NW-SE row orientation seems optimum for grape development in terms of anthocyanin concentrations (colour pigments) and ultimately improved wine quality. This however relates to a specific grape cultivar, i.e. Vitis vinifera L. cv. Shiraz/101-14 Mgt), terroir and specific wine style. Research is needed to aid our understanding of the relationships among vine phenology, light intensity (microclimate), diurnal temperature, vine row orientation and wine quality. The knowledge of the phenolic compound concentration differences of experimental Shiraz wine and the phenolic concentration association with grape cultivar is important in oenology, because the phenolic concentrations can be controlled through vineyard practices and this can lead to optimal ripeness of phenols and a desired wine style.

Poster(s)
Minnaar, P P, De Villiers, A J, Hunter, J J. 2012. Anthocyanin and sensory attributes of Vitis vinifera L. cv Shiraz wines as affected by row orientation and ripeness levels. Poster presented at the 9th International Terroir Congress. 27 June – 2 July, Dijon/Reims, France.

Minnaar, P P, De Villiers, A J, Hunter, J J. 2011. Grape ripeness and microclimate effects on the phenolic composition of grapes and wine (Vitis vinifera L. cv. Shiraz/101-14 Mgt). Poster presented at the In Vino Analytica Scientia Conference. 19-24 July, Graz, Austria.

Presentation(s)
Minnaar, P P. 2011. Grape ripeness and microclimate effects on phenolic composition of grapes and wine (Vitis vinifera L. cv Shiraz/101-14 Mgt). Paper presented at In Vino Analytica Scientia. 21-23 July, University of Technology, Graz, Austria.

Minnaar, P P and Hunter, J J. 2012. Anthocyanin and sensory attributes of Vitis vinifera L. Shiraz wines as affected by row orientation and ripeness levels. Paper presented at the 9th International Terroir Congress. 25-29 June 2012, Burgundy and Champagne, France.

Minnaar, P P, De Villiers, A J, Hunter, J J. 2014. Impact of row orientation and ripeness levels on anthocyanins and flavanols of Syrah grapes. Presented at the 36th South African Society for Enology and Viticulture Conference. 12-14 November, Somerset-West, South Africa.

Minnaar, P P, De Villiers, A J. 2014. Microclimate and grape ripeness effects on the phenolic composition of Syrah grapes and wine. Paper presented at Winetech Winemaking Techniques and Practices Programmes. 2 October.

Minnaar, P P, De Villiers, A J, Hunter, J J. 2014. Impact of row orientation and ripeness levels on anthocyanins and flavanols of Syrah grapes. Paper presented at MACROWINE. 7-10 September, Stellenbosch, South Africa.

Minnaar PP, De Villiers, A J, Hunter, J J. 2013. Anthocyanin and Sensory Attributes of Vitis vinifera L cv. Shiraz wines as affected by row orientation and ripeness levels. Paper presented at the 36th World Congress of Vine and Wine. 2-7 June, Bucharest, Romania.

Minnaar, P P, De Villiers, A J, Hunter, J J. 2013. Anthocyanins, flavanols and flavonols of Vitis vinifera L. cv Syrah wines as affected by row orientation and ripeness levels. Presentation at the 18th International Symposium of the Group of International Experts of vitivinicultural Systems for CoOperation. 7-11 July, Porto, Portugal.

Minnaar, P P, De Villiers, A J, Hunter, J J. 2013. Determination of the optimal ripeness of South African Red grapes in terms of their phenol composition. Presented at the 35th South African Society for Enology and Viticulture International Conference. 13-15 November, Somerset-West, South Africa.

Minnaar, P P, De Villiers, A J, Hunter, J J. 2012. Anthocyanin and Sensory Attributes of Vitis vinifera L cv. Shiraz wines as affected by row orientation and ripeness levels. Presented at the 34th South African Society for Enology and Viticulture Conference. 14-16 November, Franschhoek, South Africa.

Minnaar, P P, De Villiers, A J, Hunter, J J. 2012. Impact of row orientation on berry anthocyanin of Shiraz wines. Presented at the Technical Workshop-Shiraz wines. 20 November, Stellenbosch, South Africa.

Article
Minnaar, P P, De Villiers, A J, Hunter, J J. Anthocyanins, flavanols, and flavonols of Vitis vinifera L. cv Shiraz wines as affected by row orientation and ripeness levels. Proceedings of the 18th International Symposium of the Group of International Experts of vitivinicultural Systems for CoOperation, 7-11 July 2013,

Minnaar, P P, Hunter, J J. 2015. Wynkleur van Shiraz, WineLand, Mnth Dec (p. 78-79)
Article.pdf

 

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