Effect of foliar Nitrogen and Sulphur spraying on white wine composition (Vitis vinifera L.cv. Chenin Blanc and Sauvignon Blanc)

[摘要] ENGLISH ABSTRACT: Chenin Blanc and Sauvignon Blanc, as the most planted wine cultivars in South Africa, are ofgreat interest to researchers worldwide, due to its increased high wine quality. Wine quality isinterlinked with wine aroma. Vine nitrogen fertilization influence the vine physiology andcomposition of the grapes, and enhanced aroma expression. By addressing Yeast AssimilableNitrogen (YAN) deficiency with foliar fertilization, during the ripening season, to low nitrogencontaining vines, the aroma potential of the wines can be potentially influenced.The main aim of this research study was to assess the influence of different foliar fertilizationtreatments on Chenin Blanc and Sauvignon Blanc vines planted in various locations in SouthAfrica. For each season, two vineyards with a history of producing low nitrogen content grapeswere used, one vineyard per cultivar. The vineyards received sulphur and nitrogen foliartreatments twice before véraison. During winemaking, the juices and wines underwent analysisfor non-volatile and volatile content. The wines underwent maturation for three and nine months,and then sensorially and chemically analysed.In Chapter 2 the various wine compounds and classes of compounds present in Chenin Blancand Sauvignon Blanc wines were analysed. The specific characteristics, aroma composition andits implications on the sensory perception of the cultivars were reviewed. The influence andcontribution of different fertilization practices on the chemical compounds and resulting wine'saromatic expression were investigated.The first part of the research study investigated the effect of foliar fertilization on the non-volatilecontent in the juices and wines. In Chapter 3, the nitrogen containing foliar fertilization applicationsincreased the YAN levels. This increase is relevant not only for yeast metabolism, but also for thearomatic potential of a wine, as certain amino acids being precursors of aroma compounds.Glutathione were also influenced by the treatments for both years and both cultivars, but thetrends were not as evident as with YAN.The second part of the study assessed the effect of various fertilization treatments on the volatilecontent of the juices and aged wines. Sensory analysis and chemical analysis were used toassess the wines after three and nine months of bottle maturation. Chapter 4 highlighted thatsulphur containing foliar treatments influenced the volatile content of major volatiles and volatilethiols. The overall volatile content of the wines was very similar but identified a clear vintage andage effect during maturation. Sensory analysis classified the Chenin Blanc wine with 'tropical' and'fruity' aromas, while Sauvignon Blanc wines had prominent 'tropical', 'passion fruit', and'grapefruit' aromas. During bottle maturation, some notes and aroma characters were maintainedbut their frequency of citations changed.The results of this research study contributed to the knowledgebase on South African CheninBlanc and Sauvignon Blanc wines, but also concluded that foliar fertilization can influence thenon-volatile and volatile content of wines. South African winemakers and the industry can use thisinformation to make decisions at the viticulture and winemaking level to produce wines with moredesirable sensory attributes.

[发布机构] Stellenbosch University