Oenological evaluation of Chenin Blanc wines elaborated from different trellising systems

Iipinge, Hilaria (2019-12)

Thesis (MScAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Grape composition plays a significant role in defining wine style and typicality; and there are ways in which grape composition can be altered or modified. Among these ways are viticultural practices which include trellising systems. Trellising systems are driving mechanisms that alter canopy microclimates, consequently affecting yield and the quality of grapes. Due to the fact that most grape primary metabolites contribute to the production of secondary compounds in final wines, it is important to assess if changes in canopy microclimates induced by trellising systems can reflect in final wines. Therefore, the aim of this study was to characterise (chemically and sensorially) grape must and wines of Chenin Blanc grapes made from grapes of different trellising systems. Basic oenological parameters (including Brix, pH, TA and alcohol) were measured for grape juice from harvest and then throughout the winemaking process. Sugar level varied in the first season with a significant difference between systems, but no significant differences were observed in other parameters. The other important factor evaluated was yield, which had differences between systems; mostly, open canopies by horizontal division produced higher yield than vertical dividing canopies and closed non-dividing canopy systems. However, those differences were not statistically significant between systems. YAN, ammonia, total (FAN) and individual amino acids in musts and major volatiles and thiols were subsequently measured. The concentrations were above critical levels for YAN. No significant differences were found across all the treatments, when the data were subjected to analysis of variance, and even by multivariate analysis no distinctive groupings were formed. However, the additional fingerprint of wine samples by high-resolution mass spectrometry produced groupings of samples according to trellising systems. In Chapter 3, the wines of the six different trellising systems were profiled using a rapid descriptive method (CATA), using both analytical and expert panellists; further, wine overall quality was evaluated by experts. Wine samples could not be differentiated by aroma according to trellising systems. On the other hand, taste and mouthfeel profiles implied that there were differences between wine samples according to trellising systems. Additionally, the overall wine quality rating showed significant differences between wines of according to trellising systems, mostly contributed by significant differences in taste and aroma ratings. In Chapter 4, a detailed discussion of results from Chapters 2 and 3 is presented by comparing sensory profiles with chemical composition by correspondence analysis and principal component analysis respectively. Aroma compounds showed no significant differences between trellising systems (Chapter 2). Aroma description profiles from the correspondence analysis (CA) biplot (Chapter 3), illustrated that aroma profiles of the wines were similar since no clear groupings observed., The CA score plot from taste and mouthfeel results produced a similar configuration pattern with the PCA score plot from the high resolution mass spectrometry (HRMS) data, which indicated that the trellis system may have an influence on chemical aspects also related to the wines’ taste perception. The results of this research contribute to information that winemakers or growers may require regarding decisions they can make in relation to choosing an appropriate trellising systems. However, other factors such as cultivar, climate, vintage, and economic advantage should not be disregarded.

AFRIKAANSE OPSOMMING: Druiwesamestelling speel 'n belangrike rol in die definiëring van wynstyl en tipiesheid; en daar is maniere waarop druiwesamestelling verander of gewysig kan word. Onder hierdie maniere is wingerdboukundige praktyke, wat stelsels insluit. Opknappingstelsels is dryfmeganismes wat die mikroklimaat van die lug beïnvloed, wat die opbrengs en die kwaliteit van druiwe beïnvloed. Aangesien die meeste druif primêre metaboliete bydra tot die produksie van sekondêre verbindings in finale wyne, is dit belangrik om te bepaal of veranderinge in die kloofmikroklimaat wat deur trilstelsels veroorsaak word, in finale wyne kan weerspieël. Daarom was die doel van hierdie studie om druiwemost en wyne van Chenin Blanc-druiwe (wat chemies en sintuiglik is) te karakteriseer (chemies en sintuiglik), vervaardig uit druiwe van verskillende opknappingstelsels. Basiese oenologiese parameters (insluitend Brix, pH, TA en alkohol) is vanaf die oes en daarna gedurende die wynmaakproses gemeet vir druiwesap. Die suikervlak het in die eerste seisoen gewissel met 'n beduidende verskil tussen stelsels, maar in ander parameters is geen noemenswaardige verskille waargeneem nie. Die ander belangrike faktor wat geëvalueer is, was opbrengs, wat verskille tussen stelsels gehad het; Meestal het oop afdakke deur horisontale verdeling hoër opbrengste gelewer as vertikale skeidende afdakke en geslote afdakke nie. Hierdie verskille was egter nie statisties beduidend tussen stelsels nie. Daarna is YAN, ammoniak, totaal (FAN) en individuele aminosure in mossies en belangrikste vlugtige en toile gemeet. Die konsentrasies was bo kritieke vlakke vir YAN. Daar was geen noemenswaardige verskille tussen al die behandelings nie, toe die data aan variansie-analise onderworpe was, en selfs deur multivariate analise, is daar geen onderskeidende groeperings gevorm nie. Die bykomende vingerafdruk van wynmonsters deur massa-spektrometrie met 'n hoë resolusie het groepe monsters volgens trilstelsels opgelewer. In hoofstuk 3, is die wyne van die ses verskillende opleistelsels met behulp van 'n vinnige beskrywende metode (CATA) geprofileer, met behulp van sowel analitiese as kundige paneellede; verder is wyngehalte meestal deur kundiges beoordeel. Wynmonsters kon nie volgens aroma onderskei word deur aroma nie. Aan die ander kant het smaak- en mondgevoelsprofiele geïmpliseer dat daar verskille tussen wynmonsters volgens trilstelsels was. Daarbenewens het die algehele wynkwaliteitwaardigheid beduidende verskille getoon tussen wyne volgens traliewerkstelsels, meestal bygedra deur beduidende verskille in smaak- en aroma-graderings. In Hoofstuk 4, word 'n gedetailleerde bespreking van die resultate uit hoofstuk 2 en 3 aangebied deur sensoriese profiele met chemiese samestelling onderskeidelik deur korrespondensie-analise en hoofkomponentanalise te vergelyk. Aroma verbindings het geen noemenswaardige verskille getoon tussen die stelsels nie (hoofstuk 2). Aroma-beskrywings profiele uit die korrespondensie-analise (CA) biplot (Hoofstuk 3), illustreer dat die aroma-profiele van die wyne soortgelyk was, aangesien geen duidelike groeperings waargeneem is nie. Die CA-telling van smaak en mondgevoelens het 'n soortgelyke konfigurasiepatroon met die PCA-telling opgelewer Dit is gebaseer op die data met die hoë resolusie massaspektrometrie (HRMS), wat aangedui het dat die trellis-stelsel 'n invloed kan hê op chemiese aspekte wat ook verband hou met die smaakpersepsie van die wyne. Die resultate van hierdie navorsing dra by tot inligting wat wynmakers of produsente mag benodig rakende besluite wat hulle kan neem met betrekking tot die keuse van 'n toepaslike versieringstelsel. Ander faktore soos kultivar, klimaat, oesjaar en ekonomiese voordeel moet egter nie buite rekening gelaat word nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107185
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