Chemical and sensory profiling of dry and semi-dry South African Chenin blanc wines

Van Antwerpen, Lindi (2012-12)

Thesis (MSc)--Stellenbosch University, 2012.

Thesis

ENGLISH ABSTRACT: Chenin blanc wine is of economic importance to South Africa and a range of diverse dry and semi-dry wines are locally produced in this genre. Currently, the use of three distinctly different style names, each aimed at providing consumers with information about the flavour of the wines, is encouraged by the South African (SA) wine industry. The styles are fresh and fruity (FF), rich and ripe unwooded (RRUW) and rich and ripe wooded (RRW). Feedback from retail sectors over the past few years, however, repeatedly suggested that the style names are perceived as confusing by SA consumers. This master study was undertaken to re-evaluate the FF, RRUW and RRW style classification, based on both the volatile fermentation-derived aroma composition and the sensory attributes of a set of wines containing all the styles under investigation. For the purposes of chemical profiling, a set of 105 commercial Chenin blanc wines, selected to be representative of these three styles and originating from the major SA wine producing areas, were analysed by Gas Chromatography (GC) to quantify fermentation-derived volatile aroma compounds in the wines. ANOVA performed on the chemical data showed that 29 compounds represent significant differences between at least two of the 3 styles (FF, RRUW and RRW). Principal component analysis (PCA) of the volatile compounds showed a large degree differentiation between FF and RRW wine styles, however, RRUW wine styles overlapped with the other two styles. Considering vintage effects, ANOVA indicated no significant differences within FF (vintages 2009 and 2010) and RRW (vintages 2008 and 2009) styles, whereas only 2 esters and 4 terpenes showed significant differences between the three wine producing regions investigated for this purpose, Paarl/Wellington, Breede River and Stellenbosch. Volatile aroma compounds generated for Chenin blanc were included in the Winetech database consisting of the most important cultivars of South Africa. Combining the data for the volatiles for Chardonnay and Sauvignon blanc from this database and the data for Chenin blanc obtained in this study, a PCA indicated a clear separation between Chenin blanc and the other two white cultivars. Sensory evaluation of the style classification was done by two separate sensory tests. Firstly, a sorting task was performed by wine industry experts to categorise 21 Chenin blanc wines (FF, RRUW and RRW) based on their similarity. The results showed a differentiation between FF and RRW styles, however, RRUW was mostly classified together with FF wines. This indicated a possible continuum between the three styles, as opposed to three distinct different categories, currently suggested by the style names. The second sensory analysis test, Descriptive Sensory Analysis (DSA), was performed by a trained panel to generate sensory profiles for 42 wines. ANOVA of the flavour attribute intensities between different styles once again showed significant differences between FF and RRW, with RRUW wines forming a continuum between the FF and RRW styles. These results provide valuable information that could be used by the wine industry for labelling purposes.

AFRIKAANSE OPSOMMING: Chenin blanc is van ekonomiese belang vir Suid Afrika en ‘n wye reeks droë en semi-droë wyne word plaaslik geproduseer in hierdie kategorie. Tans word die gebruik van drie duidelike verskillende stylbenamings, elkeen daarop gemik om aan die verbruiker inligting te verskaf oor die geur van die wyn, deur die Suid Afrikaanse (SA) wynindustrie aangemoedig. Die style is vars en vrugtig, ryk en ryp ongehout en ryk en ryp gehout. Terugvoer van die handelssektor oor die afgelope aantal jare, het daarop gedui dat die stylbenamings tot verwarring onder SA verbruikers lei. Hierdie meestersstudie is onderneem om die stylklassifikasie, vars en vrugtig, ryk en ryp ongehout en ryk en ryp gehout, te her-evalueer op grond van die vlugtige aroma komponente wat tydens die fermentasie proses gevorm word, asook die sensoriese eienskappe van ‘n verteenwoordigende stel wyne van elk van die style wat ondersoek is. Vir die doel van die chemiese profilering, is ‘n stel van 105 kommersiële wyne, wat geselekteer is om verteenwoordigend te wees van die drie style ondersoek en ook afkomstig is van die vernaamste SA wynproduserende streke, gebruik. Die wyne is met behulp van gas chromatografie ontleed om die vlugtige komponente wat van die fermentasie proses afkomstig is, te kwantifiseer. Die analise van variansie, het getoon dat 29 komponente statisties beduidend verskil het tussen die drie style. Hoofkomponent analise van die vlugtige komponente, het getoon dat die vars en vrugtige wyne en ryk en ryp gehoute wyne, duidelik onderskeibaar was van mekaar op grond van die vlugtige data, maar die ryk en ryp ongehoute wyne het met die ander twee style oorvleuel. In terme van oesjaar effekte, was daar geen beduidende verskille in die aroma profiele van die vars en vrugtige styl (oesjare 2009 en 2010) en ryk en ryp ongehoute styl (oesjare 2008 en 2009) nie, terwyl die konsentrasie van slegs twee esters en 4 terpene statisties beduidend verskil het tussen die wynproduserende streke Paarl/Wellington, Breederivier en Stellenbosch. Resultate van die gekwantifiseerde vlugtige komponente is in die databasis van Winetech gevoeg, waar die konsentrasies van soortgelyke komponente van die vernaamste SA wynkultivars reeds vervat is. Hoofkomponent analises van die gekombineerde resultate vir Chenin blanc, Chardonnay en Sauvignon blanc wyne, het getoon dat daar ‘n duidelike verkil tussen Chenin blanc en die ander twee wit wynkultivars was. Die sensoriese evaluerings is uitgevoer deur van twee verskillende metodes gebruik te maak. Eerstens is 21 wyne (met al drie style verteenwoordig) deur wynindustrie eksperts gesorteer op grond van die waargenome eendersheid van die onderskeie wyne en die resultate is grafies geprojekteer. Die resultate het getoon dat daar ‘n duidelike verskil waargeneem is deur die assessors tussen die vars en vrugtige styl en ryk en ryp gehoute styl. Die ryk en ryp ongehoute wyne het in die analises meer met die vars en vrugtige style geassosieer, as die ryk en ryp gehoute wyne. Die tweede sensoriese metode is uitgevoer deur sensoriese paneel wat vir die doel van hierdie studie opgelei is om die geur eienskappe van 42 wyne (al drie style verteenwoordig) te profileer. Analise van statistiese beduidende verskille tussen die voorkoms van die geurkomponente en hul intensiteite vir elke styl, het weereens aangedui dat daar ‘n kontinuum bestaan tussen die style. Hierdie resultate kan van waarde vir die wynindustrie wees in besluite rakende etikettering.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/71853
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