WINETECH Technical Yearbook 2019

Overall, both cultivars were ester- and thiol- driven. While the S and N+S treatments had some negative (cooked vegetables, sulphur and herbaceous) aromas, which can be linked to reductive sulphur compounds, we observed limited or no negative effects of the treatments overall. Although the chemical makeup of the wines changed with the applied treatments as shown by the chemical analysis results, the overall effect was not observed in the aromatic expression of the wines. This can be due to the matrix effect or the interactions of the volatile and non-volatile compounds present in the wines. FINAL WORD To our knowledge, this is the first project spanning over three seasons that examined the effect of N, S, and N+S foliar fertilisation on Chenin blanc. This study contributed to the knowledge on South African Chenin blanc and Sauvignon blanc wines, but also demonstrated that foliar fertilisation can be used to influence the non-volatile (Part 2) and volatile content of wines. This knowledge could ultimately aid researchers and w i nema ke r s unde r s t and t he s e compounds, produce a specific wine style and produce better quality wines. A better understanding of the factors linking vineyard fertilisation applications, grape heredity, climate, must and wine composition to the

sensory expression of wines need to be investigated to fully understand how these different factors can affect the sensory expression of the wines. Although statistical differences were observed between major volatile and thiol levels of foliar treatments and the control in this study, no differences were observed between the different treatments in sensory analysis. The question thus remains whether it is worthwhile to do foliar treatments for this purpose taking into account the cost involved, if there will be no perceivable difference for the taster (be it consumer or professional)? Foliar treatments can be very beneficial in some cases as seen in previous studies and in the case of low YAN vineyards in this study, and in other cases have limited effect. It must not be a practice that is simply widely followed without careful consideration of the possible outcome. SUMMARY Chemical and sensory evaluation of wines made after foliar fertilisation showed whether the effects of vineyard treatments lasted during bottle maturation. Until now, no foliar fertilisation studies have focused on determining the volatile content present in wines during bottle maturation. This aspect is relevant, since the impact of the treatments on the final wines can be temporary and the effect can only last for a

limited period. Therefore, the study of the evolution of volatile chemical compounds such as major volatiles and thiols during ageing is needed to better understand the (lasting) effects of the foliar fertilisation treatments. The information gained by performing sensory analysis during different stages of bottle maturation, can add to the knowledge base of the aroma of these wines. REFERENCES Swiegers, J.H., Bartowsky, E.J., Henschke, P.A. & Pretorius, I.S., 2005. Yeast and bacterial modulation of wine aroma and flavour. Australian Journal of Grape and Wine Research 11: 139-173. Henschke, P. & Jiranek, V., 1993. Yeasts – metabolism of nitrogen compounds. In: Wine Microbiology and Biotechnology , 77- 164. Harwood Academic Publishers, Chur, Switzerland. Selli, S., Canbas, A., Cabaroglu, T., Erten, H., Lepoutre, J-P. & Gunata, Z., 2006. Effect of skin contact on the free and bound aroma compounds of the white wine of Vitis vinifera L. cv. Narince. Food Control 17(1): 75-82. Doi: 10.1016/j.foodcont.2004.09.005. Herbst- Johnstone , M. , Ni co l au , L . & Kilmartin, P.A., 2011. Stability of varietal thiols in commercial Sauvignon blanc wines. American Journal of Enology and Viticulture 62(4): 495-502. Doi: 10.5344/ ajev.2011.11023.

Capone, D., Sefton, M., Hayasaka, Y. & Jeffery, D., 2010. Analysis of precursors to wine odorant 3-mercaptohexan-1- ol using HPCL-MS/MS: Resolution and quantitation of 3-S-cysteinylhexan-1-ol and 3-S-glutathionylhexan-1-ol. Journal of Agricultural and Food Chemistry 58: 1390-1395. Sarrazin, E., Sinkharuk, S., Pons, M., Thibon, C., Bennetau, B. & Darriet, P., 2010. Elucidation of the 1,3-sulfanylalcohol ox i d a t i on me c h a n i sm: An unu s u a l identification of the disulfide of 3-sulfa- nylhexanol in Sauternes botrytized wines. Journal of Agricultural and Food Chemistry 58: 10606-10613. Juhasz, A., 2015. Effect of foliar fertilization on wine aroma for white wine cv. Sauvignon blanc ( Vitis vinifera L.). Lacroux, F., Tregoat, O., Van Leeuwen, C., Pons, A. & Dubourdieu, D., 2008. Effect of foliar nitrogen and sulphur application on aromatic expression of Vitis vinifera L. cv. Sauvignon blanc. Journal International des Sciences de la Vigne et du Vin 42(3): 1-8. Doi: 10.1007/s11032-013-9938-5. Geffroy, O., Charrier, F. & Poupault, P. et al. , 2016. Nitrogen and sulfur spraying allow to produce wines with enhanced concentration in varietal thiols. Macrowine , 27-30 June: 81310.

– For more information, contact Astrid Buica at abuica@sun.ac.za.