Sensory profiling, quality evaluation, and chemical profiling of South African de-alcoholised still wines

Simple item page
dc.contributor.advisorNieuwoudt, Heleneen_ZA
dc.contributor.advisorBrand, Jeanneen_ZA
dc.contributor.advisorPentz, Chrisen_ZA
dc.contributor.advisorMuller, Magdalenaen_ZA
dc.contributor.authorQwebani, Sinazoen_ZA
dc.contributor.otherStellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology.en_ZA
dc.date.accessioned2023-02-27T10:24:58Z
dc.date.accessioned2023-05-18T07:05:40Z
dc.date.available2023-02-27T10:24:58Z
dc.date.available2023-05-18T07:05:40Z
dc.date.issued2023-03
dc.descriptionThesis (MScAgric)--Stellenbosch University, 2023. en_ZA
dc.description.abstractENGLISH ABSTRACT: A relatively new category of wines with <0.5% v/v ethanol produced through physical removal of ethanol is in demand by many health-conscious consumers. However, this physical intervention has an impact on the wines’ sensory profiles. Accordingly, there is an interest in understanding this category’s sensory aspects and chemical composition. The aim of this study was to investigate the sensory profiles and quality of South African (SA) de-alcoholised still wines, and to do chemical profiling, with focus on volatile aroma compounds, of the wines. The sensory profiles of a set of commercial de-alcoholised still wines (n=16) were generated by the free listing (FL) method. Wine industry professionals (n=52) from seven different wine cellars participated were asked to freely list the sensory descriptors they associated with the wines upon tasting. For quality evaluation, the same panel was required to score the wines’ perceived quality using a 20-point scale. The sensory modalities evaluated for quality were appearance (max=3), nose (max=7), and palate (max=10) added up to a score of 20. In addition, to obtain a chemical profile, chemical compounds of a wine set (n=14) were quantified. However, data processing was required for the text generated from the free listing sensory evaluation method. For instance, free listing generated 11627 words which were standardised to 3846 descriptions after removal of non-sensory descriptions, repetitions of descriptions and comparisons. Thereafter, lemmatisation was done where descriptors were reduced to their roots and grouped into descriptor categories. The established sensory profile consisted of positive, neutral, and negative descriptor categories. The results of the study reveal that negative sensory descriptors were cited many times compared to positive characteristics: “off-odours”, “lack of aroma”, “lacks flavour”, and “watery”. However, it is important to note that there were positive descriptors: “good aroma” and “good palate”. Even though, “fruit” a neutral descriptor was the most cited which might have contributed positively to the sensory quality of these wines. In overall these results lack cultivar specific descriptions and thus wine authenticity which indicates that the complex aroma and flavour profile of full-strength white, rosé and red wines can be lowered drastically due to the process of de-alcoholisation. These sensory descriptors were then correlated with quality scores attained using the 20-point scale scoring system in which some of the wines received very low scores. As a result, the average of the overall scores was 13 out 20 which is explained as “borderline faulty”, “unbalanced wine”. In addition, the concentrations of the wines under study had 4 folds less of esters, 17 folds less of higher alcohols, and 3 folds less of fatty acids when compared to published ideal wines values, depicting poor wine quality. This pioneering study has established the sensory, quality, and chemical profile of this wine for the improvement of this category. As a result, major concerns both in sensory quality and the chemical profile of this new category have been successfully identified and insights into the way forward have been recommended to the wine industry and future studies.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: 'n Relatief nuwe wynkategorie met <0.5% v/v etanol wat deur fisiese verwydering van etanol uit volsterkte wyn geproduseer word, is in aanvraag deur gesondheidsbewuste verbruikers. Hierdie fisiese ingryping het egter 'n impak op die wyne se sensoriese profiele. Gevolglik is daar 'n belangstelling om hierdie kategorie se sensoriese aspekte en chemiese samestelling te verstaan. Die doel van hierdie studie was tweeledig: om die sensoriese profiele en kwaliteit van Suid- Afrikaanse (SA) ge-dealkoholiseerde stilwyne te ondersoek, en om chemiese profilering van die vlugtige aromaverbindings te doen. 'n Paneel van 52 wynindustriedeskundiges van sewe wynkelders het die vrye notering (FL, Engels Free Listing) metode gebruik om die sensoriese beskrywings van ‘n stel van (n=16) ge- dealkoholiseerde SA stilwyne tydens die proe van die wyne te genereer. Vir kwaliteits-evaluering het dieselfde paneel die wyne se waargenome kwaliteit met behulp van 'n 20-punt skaal beoordeel. Die sensoriese modaliteite wat vir kwaliteit geëvalueer is, was voorkoms (maksimum=3 punte), aroma (maksimum=7) en palet (maksimum=10). 'n Profiel van die aromakomponente is met gas- chromatografie op 'n stel van 14 wyne gedoen. Teksdata-ontginning het ingesluit om die 11627 oorspronklike woorde te standaardiseer deur verwydering van nie-sensoriese beskrywings, sinonieme vir dieselfde konsep en vergelykings tussen wyne in die stel. Daarna is die vorming van sensoriese groepterme (Engels Lemmatisation) op die finale 3846 woorde gedoen en die terme in positiewe, neutrale en negatiewe kategorieë gegroepee. Die resultate van die studie het etlike positiewe sensoriese aspekte geïdentifiseer, o.a. "goeie aroma" en "goeie palet". Die beskrywing "vrug" ('n neutrale kategorie) is die meeste aangehaal en kon moontlik positief tot die sensoriese kwaliteit van hierdie wyne bygedra het. Heelwat negatiewe sensoriese beskrywers, o.a. “wangeure”, “gebrekkige aroma”, “gebrekkige geur” en “waterig” is genoem. Oor die algemeen is daar nie kultivarspesifieke beskrywings gegenereer nie, wat moontlik daarop dui dat die komplekse aroma- en geurprofiel van volsterkte wit-, rosé- en rooiwyne drasties verlaag kan word as gevolg van die proses van de-alkoholisering. Hierdie sensoriese beskrywings is verder gekorreleer met kwaliteittellings wat behaal is deur gebruik te maak van die 20-punt skaalpuntstelsel, met die fokus op dié wyne wat lae tellings gekry het. Die gemiddelde kwaliteit van die stel deur die hele paneel be-oordeel, was 13 uit 20, wat in die literatuur as “marginaal foutief” of “ongebalanseerd” beskryf word. Die chemiese data het getoon dat, in vergelyking met gepubliseerde vlakke vir volsterkte alkohol stilwyne, die ge-dealkoholiseerde wyne ‘n 4-voudige verlaagde vlakke van esters, 17-voudieg verlaagde vlakke van hoër alkohole, en ‘n 3-voudige vermindering van vetsuurkonsentrasies gehad het. Hierdie baanbrekerstudie het die sensoriese kwaliteit en chemiese profiele van ge-dealkoliseerde wyn vasgestel en dien as basis vir die algemene verbetering van hierdie kategorie. Aspekte waar die sensoriese kwaliteit verdure ontwikkeling verg is suksesvol geïdentifiseer in die studie en aanbevelings vir die wynbedryf en toekomstige studies is gemaak.af_ZA
dc.description.versionMastersen_ZA
dc.format.extentxii, 122 pages : illustrations (some color)en_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/127128
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshWine and wine making -- South Africaen_ZA
dc.subject.lcshWine -- Flavor and odoren_ZA
dc.subject.lcshWine -- Evaluationen_ZA
dc.subject.lcshWine -- Qualityen_ZA
dc.subject.lcshChemical profilingen_ZA
dc.subject.lcshNon-alcoholic winesen_ZA
dc.subject.lcshSensory evaluationen_ZA
dc.subject.lcshDealcoholized wines -- South Africaen_ZA
dc.subject.lcshStill wineen_ZA
dc.subject.nameUCTDen_ZA
dc.titleSensory profiling, quality evaluation, and chemical profiling of South African de-alcoholised still winesen_ZA
dc.typeThesisen_ZA
Files
Original bundle
Now showing 1 - 1 of 1
Thumbnail Image
Name:
qwebani_sensory_2023.pdf
Size:
4.4 MB
Format:
Adobe Portable Document Format
Description:
Download
Collections
Masters Degrees (Viticulture and Oenology)