Project title
Oxygen management during the winemaking process

Project leader
Du Toit, W J

Institution
University of Stellenbosch. Department of Viticulture and Oenology

Team members
Nieuwoudt, H H

Project description
The overall objectives of this project are to ascertain more knowledge regarding the role that oxygen plays in South African wines, both white and red. The first aim of the project is to investigate the effect of very oxidative and reductive winemaking on South African white wines composition and quality. Whole bunch pressing of white cultivars under almost inert atmosphere is becoming more popular in Europe, but has not been investigated according to our knowledge. By using a custom made press, oxygen levels were kept below 0.5 mg/L in the headspace. This led to higher concentrations of phenolics and glutathione. However, the presence of even low concentrations of oxygen resulted in lower concentrations of these compounds. Very reductive conditions on the other hand led to sulphur compounds being formed.

A ratio of 1/2 to 1/4 of anthocyanins to tannins is considered optimal for red wine maturation and phenolic development in combination with slight oxidation. The second aim of this study is to investigate this unsupported claim. Initial additions of white skins to red juice led to low anthocyanin concentrations and very high T/A ratios. By substituting the skins with pips, more favourable ratios were obtained. The development of these wines over time will thus be monitored.

The third aim is to ascertain whether infrared spectroscopy can be used in combination with the electronic tongue and tasting to monitor the development of oxidation in wine. This will be done in conjunction with researchers from Russia and Denmark.

Poster(s)
1. Du Toit, W J, Joseph, B, Lisjak, K, Prevoo, D and Stander, M. 2006. A novel LCMSMS method to measure gluthathione concentrations in grape juice and wine. 29th National Congress of the South African Society for Enology and Viticulture, November, Somerset West, South Africa.
2. Joesph, B, Oberholser, A, Lisjak, K and Du Toit, W J. 2006. Reductive pressing and juice treatments: effect on white wine composition. 29th National Congress of the South African Society for Enology and Viticulture, November, Somerset West, South Africa.

Presentation(s)
1. Du Toit, W J, Joseph, B and Nieuwoudt, H H. 2006. Alternative ways to measure oxidation in wine. 29th National Congress of the South African Society for Enology and Viticulture, November, Somerset West, South Africa.
2. Du Toit, W J and Lisjak, K. 2006. Knowledge transfer to industry as a presentation: Reductive winemaking in South African Sauvignon blanc. SASEV, Cape Winelab. SA Wine Laboratories seminar, Stellenbosch, South Africa.
3. Du Toit, W J. 2006. Reductive winemaking with Sauvignon blanc. Interlab Information Day, Elsenburg Agricultural College, Stellenbosch, South Africa.
4. Du Toit, W J. 2007. Oxygen in wine. 58th Annual American Society of Enology and Viticulture's Annual Meeting. Reno, Nevada.
5. Du Toit, W J. 2008. Over ageing of white wines. Vinpro Consultation Services Information Day, Barrydale, South Africa.
6. Geldenhuys, L, Oberholster, A and Du Toit, W J. 2008. The effect of macro-oxygenation on wines made of different seed concentrations. 15th International Enology Symposium, Trier, Germany.
7. Geldenhuys, L, Oberholster, A and Du Toit, W J. 2008. The effect of macro-oxygenation on wines made of different seed concentrations. Dienstleistungszentrum Landlicher Raum, Neustadt, Germany.

Final report
http://www.sawislibrary.co.za/dbtextimages/DuToitWJ2.pdf

Du Toit, W J. 2006. Nuwe bevindige rakende askorbiesuur in wyn. WineLand. Mnth July v. 203 p. 63-64

Article

Du Toit, W J. 2006. Nuwe bevindings rakende askorbiensuur in wyn. WineLand. Mnth Jul n. 203 p. 63-64

Du Toit, W J, Lisjak, K, Stander, M A, Prevoo, D. 2007. Using LC-MSMS to assess glutathione levels in South African white grape juices and wines made with different levels of oxygen. Journal of Agricultural and Food Chemistry. v. 55 p. 2765-2769

Du Toit, W J. 2007. Effect of different oxygen levels on glutathione levels in South African white must and wines. WineLand. Mnth Dec n. 220 p. 66-67

Du Toit, W J. 2006. The effect of oxygen on the composition and microbiology of red wine. (PhD)

Dissertation

Lisjak, K. 2007. The role of oxygen in new vinification technologies of white and red wines (PhD)

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