WINETECH Technical Yearbook 2021

Control

C + Cu C + MeSH C + MeSH + Cu

C + H2S C + H2S + Cu C + H2S + MeSH

C + H2S + MeSH + Cu

Passionfruit - after 24 hours vs 6 weeks (Graph 2) Graph 2: Passion fruit – after 24 hours vs 6 weeks

chromatography with sulfur chemilumines- cence detection. Journal of Agricultural and Food Chemistry 58(17): 9454-9462. Doi: 10.1021/jf102008r. Nikolantonaki, M. & Waterhouse, A.L., 2012. A method to quantify quinone reaction rates with wine relevant nucleophiles: A key to the understanding of oxidative loss of varietal thiols. Journal of Agricultural and Food Chemistry 60(34): 8484 - 8491. Doi: 10.1021/jf302017j. Coetzee, C. & Du Toit, W.J., 2012. A compre - hensive review on Sauvignon blanc aroma with a focus on certain positive volatile thiols. Food Research International 45(1): 287-298. Doi: 10.1016/j.foodres.2011.09.017. Franco-Luesma, E., Sáenz-Navajas, M.P., Valentin, D., Ballester, J., Rodrigues, H. & Ferreira, V., 2016. Study of the effect of H2S, MeSH and DMS on the sensory profile of wine model solutions by Rate- All-That-Apply (RATA). Food Research International 87: 152-160. Doi: 10.1016/j. foodres.2016.07.004.

Contributing researchers: Marlize Bekker and Allie Kulcsar. REFERENCES Clark, A.C., Grant-Preece, P., Cleghorn, N. & Scollary, G.R., 2015a. Copper(II) addition to white wines containing hydrogen sulfide: Re - sidual copper concentration and activity. Aus­ tralian Journal of Grape and Wine Research 21(1): 30-39. Doi: 10.1111/ajgw.12114. Clark, A.C., Wilkes, E.N. & Scollary, G.R., 2015b. Chemistry of copper in white wine: A review. Australian Journal of Grape and Wine Research 21(3): 339-350. Doi: 10.1111/ajgw.12159. Vela, E., Hernández-Orte, P., Franco-Luesma, E. & Ferreira, V., 2017. The effects of copper fining on the wine content in sulfur off-odors and on their evolution during accelerated anoxic storage. Food Chemistry 231: 212- 221. Doi: 10.1016/j.foodchem.2017.03.125. Ugliano, M., Kwiatkowski, M., Vidal, S. et al. , 2011. Evolution of 3-mercaptohexanol, hydrogen sulfide, and methyl mercaptan during bottle storage of Sauvignon blanc wines. Effect of glutathione, copper, oxygen exposure, and closure-derived oxygen. Journal of Agricultural and Food Chemistry 59(6): 2564-2572. Doi: 10.1021/jf1043585. Siebert, T.E., Solomon, M.R., Pollnitz, A.P. & Jeffery, D.W., 2010. Selective determination of volatile sulfur compounds in wine by gas

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Control

C + Cu C + MeSH C + MeSH + Cu

C + H2S C + H2S + Cu C + H2S + MeSH

C + H2S + MeSH + Cu

24 hours 6 weeks

wine with reductive off-odours, this is the take-home message from this experiment: Copper is effective in binding H 2 S and removing its “boiled egg” off-odour, while less effective in mitigating MeSH-derived “cabbage” off-odour from the wine. A small- scale trial with copper addition to remove H 2 S could be beneficial, to determine what is the minimum amount necessary to remove the reductive off-odour from the wine. From this study’s results, it is possible to conclude that after the copper has bound to H 2 S, excess copper could gradually bind to the desirable varietal thiol 3MH in your wines after bottling and reduce tropical notes in e.g., Sauvignon blanc and Chenin blanc wines. Therefore, good winemaking

practice would be to avoid reductive odours from forming in wines. If not possible, then to mindfully use copper in the removal of reductive off-odours by using only the minimum amount necessary. SUMMARY Researchers at the South African Grape and Wine Research Institute (SAGWRI) at Stellenbosch University partnered with researchers from the Australian Wine Research Institute (AWRI) in Adelaide, to expand knowledge on the short- and long-term chemical and sensorial impacts of copper fining of reductive wines. The project provided new insights on this controversial topic.

For more information, contact Matija Leskovi ć at matija@sun.ac.za.

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