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

Thesis (MA)--Stellenbosch University, 2018.ENGLISH ABSTRACT: Chenin Blanc and Sauvignon Blanc, as the most planted wine cultivars in South Africa, are of great interest to researchers worldwide, due to its increased high wine quality. Wine quality is interlinked with wine aroma. Vine nitrogen fertilization influence the vine physiology and composition of the grapes, and enhanced aroma expression. By addressing Yeast Assimilable Nitrogen (YAN) deficiency with foliar fertilization, during the ripening season, to low nitrogen containing 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 fertilization treatments on Chenin Blanc and Sauvignon Blanc vines planted in various locations in South Africa. For each season, two vineyards with a history of producing low nitrogen content grapes were used, one vineyard per cultivar. The vineyards received sulphur and nitrogen foliar treatments twice before véraison. During winemaking, the juices and wines underwent analysis for 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 Blanc and Sauvignon Blanc wines were analysed. The specific characteristics, aroma composition and its implications on the sensory perception of the cultivars were reviewed. The influence and contribution of different fertilization practices on the chemical compounds and resulting wine’s aromatic expression were investigated. The first part of the research study investigated the effect of foliar fertilization on the non-volatile content in the juices and wines. In Chapter 3, the nitrogen containing foliar fertilization applications increased the YAN levels. This increase is relevant not only for yeast metabolism, but also for the aromatic 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 the trends were not as evident as with YAN. The second part of the study assessed the effect of various fertilization treatments on the volatile content of the juices and aged wines. Sensory analysis and chemical analysis were used to assess the wines after three and nine months of bottle maturation. Chapter 4 highlighted that sulphur containing foliar treatments influenced the volatile content of major volatiles and volatile thiols. The overall volatile content of the wines was very similar but identified a clear vintage and age 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 maintained but their frequency of citations changed. The results of this research study contributed to the knowledgebase on South African Chenin Blanc and Sauvignon Blanc wines, but also concluded that foliar fertilization can influence the non-volatile and volatile content of wines. South African winemakers and the industry can use this information to make decisions at the viticulture and winemaking level to produce wines with more desirable sensory attributes.AFRIKAANSE OPSOMMING: Chenin Blanc en Sauvignon Blanc is die mees aangeplante witwyn-kultivars in Suid-Afrika en is van groot belang vir navorsers wêreldwyd weens die hoë wynkwaliteit. Wynkwaliteit is gekoppel aan wyn aroma. Stikstof bemesting tot die wingerdstok kan die wingerd fisiologie en samestelling van die druiwe beïnvloed, asook die aroma uitdrukking verbeter. Deur die gisbare stikstof (YAN) tekort aan te vul in lae stikstofbevattende wingerde met blaarvoeding gedurende die rypwording seisoen, kan die aroma van die wyne potensieël beïnvloed word. Die hoofdoel van hierdie navorsing studie was om die invloed van verskillende blaarvoeding behandelinge op Chenin Blanc- en Sauvignon Blanc wingerdstokke op verskillende plekke in Suid-Afrika te beoordeel. Vir elke seisoen is twee wingerde met 'n geskiedenis van lae druif stikstofinhoud gebruik, een wingerd per kultivar. Die wingerd het twee keer voor deurslaan swaelen stikstof-blaartoevoegings ontvang. Tydens die wynmaakproses is die sappe en wyne geanaliseer vir nie-vlugtige en vlugtige inhoud en het onderskiedelik vir drie en nege maande veroudering ondergaan en is daarna sensories en chemies ontleed. In Hoofstuk 2 is verskillende wynverbindings en klasse van verbindings wat teenwoordig is in Chenin Blanc- en Sauvignon Blanc wyne geanaliseer. Die spesifieke eienskappe, aromasamestelling en uitwerking daarvan op die sensoriese persepsie van die kultivars is geevalueer. Die invloed en bydrae van verskillende blaarvoeding behandelinge op die chemiese verbindings en gevolglike aromatiese uitdrukking van die wyne is ondersoek. Die eerste deel van die navorsing het ondersoek ingestel op die effek van blaarvoeding op die nie-vlugtige inhoud in die sappe en wyne. In Hoofstuk 3 het die stikstofbevattende blaarvoeding behandelinge die YAN-vlakke verhoog. Hierdie toename is nie net relevant vir gismetabolisme nie, maar ook vir die aromatiese potensiaal van 'n wyn, aangesien sekere aminosure voorlopers van aromaverbindings is. Glutatione was ook beïnvloed deur die behandelings vir beide jare en albei kultivars, maar die neigings was nie so duidelik soos met YAN nie. Die tweede deel van die studie het die effek van verskillende blaarvoeding behandelinge geevalueer op die vlugtige inhoud van die sappe en verouderde wyne. Sensoriese - en chemiese analise is gebruik om die wyne na drie en nege maande se bottelveroudering te beoordeel. Hoofstuk 4 het uitgewys dat swael-blaartoevoegings die vlugtige inhoud van esters, hoër alkohole, vetsure en positiewe vlugtige tiole beïnvloed het. Die algehele vlugtige inhoud van die wyne was baie soortgelyk, maar het 'n duidelike oesjaar en verouderingseffek tydens veroudering getoon. Sensoriese analise het die Chenin Blanc wyn met 'tropiese' en 'vrugtige'-aromas geklassifiseer, terwyl Sauvignon Blanc wyne prominente' tropiese', ‘grenadella' en ‘pomelo' aromas gehad het. Tydens bottelveroudering is die teenwoordigheid van sommige aromatiese karakters behou, maar die hoeveelheid keer wat dit voorkom het verander. Resultate van hierdie navorsing studie het bygedra tot die kennisbasis oor die Suid-Afrikaanse Chenin Blanc- en Sauvignon Blanc wyne, maar het ook tot die gevolgtrekking gekom dat blaarvoeding behandelinge die nie-vlugtige en vlugtige inhoud van wyne kan beïnvloed. Suid- Afrikaanse wynmakers en die bedryf kan hierdie inligting gebruik om besluite te neem op wingerdbou en wynmaak om wyne met meer wenslike sensoriese eienskappe te produseer