Role of varietal thiols in South African Colombard wines

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dc.contributor.advisorDu Toit, Wessel J.en_ZA
dc.contributor.advisorBrand, Jeanneen_ZA
dc.contributor.authorVan Rooyen, Riancoen_ZA
dc.contributor.otherStellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology.en_ZA
dc.date.accessioned2019-02-25T10:16:07Z
dc.date.accessioned2019-04-17T08:15:00Z
dc.date.available2023-05-03T03:00:14Z
dc.date.issued2019-04
dc.descriptionThesis (MScAgric)--Stellenbosch University, 2019.en_ZA
dc.description.abstractENGLISH ABSTRACT: Colombard is the second most planted wine grape in South Africa and research that provides insight into and additional knowledge on Colombard may prove particularly useful in the production of quality wine from this cultivar. One of the most important quality drivers is wine aroma. The aroma of a wine may be studied through the quantification of certain compounds, as well as through sensory analysis. There are limited studies that have focused on quantifying the compounds responsible for the aroma of Colombard wine. Varietal thiols are sulphur-containing compounds and include 3-mercaptohexan-1-ol (3MH), 3-mercaptohexyl acetate (3MHA) and 4-mercapto-4-methylpentan-2-one (4MMP). These varietal thiols are normally present at extremely low levels in wine and have been known to contribute to the aromas of ‘passion fruit’, ‘guava’ and other ‘fruity aromas’ in Sauvignon Blanc and Chenin Blanc wines. The aims of this research were to determine whether certain viticultural and oenological practices may influence varietal thiol levels in Colombard wine and to explore the sensory contribution of varietal thiols to the aroma of South African Colombard wine. The effects of different vineyards, yeast strains and juice treatments on varietal thiols levels in Colombard wine were investigated. A classification of commercial wines in terms of the effect of different winemaking practices on varietal thiol levels was also undertaken. The sensory contribution of varietal thiols to the aroma of Colombard wines was also assessed. The origin of the grapes, as well as the choice of yeast strain, significantly influenced 3MH levels, while the latter also had a significant effect on 3MHA levels. Certain juice treatments were found to lead to large increases in 3MH and 3MHA levels. Varietal thiols in commercial Colombard wines were comparable to those reported in young South African Sauvignon Blanc and Chenin Blanc wines. Significant differences in varietal thiol levels were found for the origin of the grapes (3MH), vineyard yield (4MMP), method of juice clarification (3MH), and the bulk price point of the wine (3MH and 3MHA). Varietal thiols seem to play an important role in the ‘guava’ and ‘passion fruit’ aromas in South African Colombard wines. The results of this research have made a contribution to the sensorial characterisation of Colombard wines. With this new knowledge, viticultural and oenological decisions may be adapted to produce market-specific Colombard wines.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Colombard is die tweede mees geplante wyndruif in Suid-Afrika en navorsing wat insig in en bykomende kennis oor Colombard verskaf, kan veral nuttig wees in die produksie van gehalte wyn met hierdie kultivar. Een van die belangrikste drywers van gehalte is wynaroma. Die aroma van ’n wyn kan bestudeer word deur die kwantifisering van sekere verbindings, asook deur sensoriese analise. Daar is beperkte studies wat fokus op die kwantifisering van verbindings wat verantwoordelik is vir die aroma van Colombard-wyn. Variëteitspesifieke tiole is swaelbevattende verbindings en sluit in 3-merkaptoheksaan-1-ool (3MH), 3-merkaptoheksiel asetaat (3MHA) en 4-merkapto-4-metielpentaan-2-oon (4MMP). Hierdie variëteitspesifieke tiole is normaalweg teen baie lae vlakke in wyn teenwoordig en dit is bekend dat hulle bydra tot die ‘grenadella’-, ‘koejawel’- en ander ‘vrugtige aromas’ in Sauvignon Blanc- en Chenin Blanc-wyn. Die doelstellings van hierdie navorsing was om te bepaal of sekere wingerdkundige en wynkundige praktyke die vlak van variëteitspesifieke tiole in Colombard-wyn kan beïnvloed en om die sensoriese bydrae van variëteitspesifieke tiole tot die aroma van Suid-Afrikaanse Colombard-wyn te ondersoek. Die effekte van verskillende wingerde, gisrasse en sapbehandelings op die vlak van variëteitspesifieke tiole in Colombard-wyn is bestudeer. Verder is ’n klassifikasie van kommersiële wyne in terme van die effek van verskillende wynbereidingspraktyke op die vlak van variëteitspesifieke tiole onderneem. Die sensoriese bydrae van variëteitspesifieke tiole tot die aroma van Colombard-wyn is ook assesseer. Die oorsprong van die druiwe, sowel as die keuse van gisras, het ’n betekenisvolle invloed op die vlak van 3MH gehad, terwyl laasgenoemde ook ’n betekenisvolle effek op die vlak van 3MHA gehad het. Sekere sapbehandelings is gevind om groot verhogings in 3MH- en 3MHA-vlakke teweeg te bring. Variëteitspesifieke tiole in kommersiële Colombard-wyn kon vergelyk word met wat in jong Suid-Afrikaanse Sauvignon Blanc- en Chenin Blanc-wyn gevind is. Betekenisvolle verskille in die vlakke van variëteitspesifieke tiole is gevind vir die oorsprong van die druiwe (3MH), wingerdopbrengs (4MMP), manier van sapverheldering (3MH), en die grootmaatprys van die wyn (3MH en 3MHA). Dit het geblyk dat variëteitspesifieke tiole ’n belangrike rol speel in die ‘koejawel’- en ‘grenadella’-aromas van Suid-Afrikaanse Colombard-wyn. Die resultate van hierdie navorsing maak ’n bydrae tot die sensoriese karakterisering van Colombard-wyn. Met behulp van hierdie nuwe kennis kan wingerdkundige en wynkundige besluite aangepas word om markspesifieke Colombard-wyn te produseer.af_ZA
dc.embargo.terms2023-04-30
dc.format.extent89 pages : illustrations, mapen_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/105835
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshWine and wine makingen_ZA
dc.subject.lcshColombard wine grapes -- South Africaen_ZA
dc.subject.lcshVarietal thiol levels in Colombard wineen_ZA
dc.subject.lcshThiols -- Analysisen_ZA
dc.subject.lcshWine -- Flavor and odoren_ZA
dc.subject.lcshColombard wine grapes -- Effect of stress onen_ZA
dc.subject.lcshGrapes -- Sensory evaluationen_ZA
dc.subject.lcshGrapes -- Selectionen_ZA
dc.subject.nameUCTDen_ZA
dc.titleRole of varietal thiols in South African Colombard winesen_ZA
dc.typeThesisen_ZA
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