WINETECH Technical Yearbook 2019

applications at véraison on Chenin blanc and Sauvignon blanc in South Africa. Such research was therefore required to compare the outcome to previous trials (Sauvignon blanc) to evaluate foliar fertilisation in local context (Chenin blanc and Sauvignon blanc) and to contribute to the knowledge regarding Chenin blanc as a whole. SOUTH AFRICAN PROJECT AIMS AND OBJECTIVES The limitations of the previous foliar fe r t i l i s a t i on s t ud i e s a r e l i n ked t o both chemi ca l and sensor y aspec t s . Methoxypyrazines and major volatiles are important aroma compounds and have not been analysed in foliar fertilisation research studies. Only a few research studies determined the vine nitrogen status before and after foliar applications (Jreij et al ., 2009; Lacroux et al ., 2008; Helwi et al ., 2014). Only two studies have done sensory analysis of the finished wines, but do not mention the age of the wines (Lacroux et al ., 2008; Geffroy et al ., 2016). Another gap in foliar fertilisation research studies is that chemical and sensory evolution of wines during bottle maturation have not been considered. To this end, a project was proposed to study the effect of N and S foliar fertilisation treatments on the chemical composition of the juice and wine of V. vinifera L. cultivars Chenin blanc and Sauvignon blanc. This was

accomplished by evaluating the treatment effects on non-volatile content (amino acids, GSH and YAN) at various stages of winemaking and on volatile composition (major volatiles, methoxypyrazines and volatile thiols) in wine. Furthermore, the effect on the aroma composition of the wines was evaluated sensorially. These aspects constitute the topic of the next two articles in the series. SUMMARY Positive results of foliar fertilisation studies in vineyards have gained the attention of South Africa’s wine industry and winemakers who want to positively influence the aroma and complexity of wines through this viticultural practice. The complexity of the various chemical compounds present in the grape berry and must can contribute to the intricate aromatic expression, flavour and mouth- feel properties of a wine. Many winemakers and viticulturists have experimented with various processes in the cellar or practices in the vineyard to positively influence the non- volatile and volatile compounds present in grapes and wine. Vine nitrogen fertilisation has been shown to have a positive impact on the composition of grapes. Due to climate change and frequent summer droughts, foliar fertilisation has been widely used on various crops and can lead to a quick nutrient uptake through the leaves.

Christensen, L.P., Smart, D.R. 2005. Foliar fertilization in vine mineral nutrient management programs. In: Soil Environment and Vine Mineral Nutrition Symposium. 83-90. Jreij, R., Kelly, M.T., Deloire, A., Brenon, E., Blaise, A. 2009. Combined effects of soil- applied and foliar-aplied Nitrogen on the N composition and distribution in water stressed vitis vinifera L. cv. Sauvignon blanc grapes. Journal International des Sciences de la Vigne 43(4):179-187. Lasa, B., Menendez, S., Sagastizabal, K., et al . 2012. Foliar application of urea to “Sauvignon blanc” and “Merlot ” vines: Doses and time of application. Plant Growth Regulation 67(1):73-81. Doi: 10.1007/ s10725-012-9667-5. Delas, J. 2000. Fertilisation de La Vignee. 2nd ed. (Féret, ed.). Bordeaux. Marais, J. 1994. Sauvignon blanc cultivar aroma: A review. South African Journal of Enology and Viticulture 15(2):41-45. Loubser, F. 2008. Chenin blanc table wine in South Africa. Cape Wine Master Dissertation. http://capewineacademy.co.za/ dissertations/Cheninblanc_Table_Wines.pdf . Monteiro, F.F., Bisson, L.F. 1991. Biological Assay of Nitrogen Content of Grape juice and prediction of sluggish fermentations. American Journal of Enology and Viticulture 42(1):47-57.

REFERENCES Bell, S.J., Henschke, P.A. 2005. Implications of nitrogen nutrition for grapes, fermentation and wine. Australian Journal of Grape and Wine Research 11(3):242-295. Doi: 10.1111/ j.1755-0238.2005.tb00028.x. Chone, X., Lavigne-Cruege, V., Tominaga, T., et al . 2006. Effect of wine nitrogen status on grape aromatic potential: Flavor precursors (S-cysteine conjugates), gluthathione and phenolic content in *Vitis vinifera* L. cv. Sauvignon blanc. Journal International des Sciences de la Vigne et du Vin 1-6. Doi: 10.1006/anbo.2000.1361. Fischer, U. Flavours and fragrances. 2007 In: Flavours and Fragrances : Chemistry, Bioprocessing and Sustainability. Berlin, Heidelberg, New York: Springer. 241-67. Doi: 10.1016/S0924-2244(97)01044-3. Laget, F., Tondut, J-L., Deloire, A., Kelley, M.T. 2008. Climate trends in a specific Mediterranean viticultural area between 1950 and 2006: Climate and viticulture in the South of France. Journal International des Sciences de la Vigne et du Vin 42(3):113-123. http:// knol.google.com/k/alain-deloire/climate- trends-in-a-specific/2rmh6zvf1o8hc/12 . Keller, M. 2010. Water Relations and Nutrient Uptake. In: The Science of Grapevines: Anatomy and Physiology. 1st ed. Elsevier Inc. 85-105. Doi: 10.1016/B978-0-12-374881- 2.00003-9.