Characterization of Chenin Blanc wines produced by natural fermentation and skin contact : focus on application of rapid sensory profiling methods

Weightman, Jayne (2014-12)

Thesis (MSc)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: Producers of South African (SA) dry and semi-dry Chenin blanc table wines are currently experimenting with winemaking techniques to modulate the flavours of the predominantly fruity styles of this genre. An important stage during wine style development is sensory profiling paired with consumer acceptance testing, before wine is produced on industrial scale. With those aforementioned goals in mind, this study was conducted in partnership with two commercial SA wine cellars. The main focus of the study was an investigation into the treatment effects of two winemaking techniques, respectively grape skin contact and natural fermentation, on the sensory profiles of experimentally produced Chenin blanc wines. Results obtained with descriptive sensory analysis (DA) of the wines were compared to those obtained by two rapid sensory profiling methods, namely projective mapping (PM) and frequency of attribute citation (FC). A consumer preference study was also done on the wines. In order to understand the treatment effects better, the dominant non-Saccharomyces yeasts that were present during the natural fermentations were identified using polymerase chain reaction (PCR), while the major volatile chemical compounds were identified with chromatography and mass spectrometry. The sensory and chemical profiles of the naturally fermented wines were significantly different from those of the inoculated wines. PCR analysis identified some of the yeasts present during alcoholic fermentation. In comparison to the inoculated fermented wines, the naturally fermented wines were generally perceived to have more intense and riper tropical fruity aromas, with enhanced sweetness and reduced intensities of sourness, bitterness and astringency. The wines fermented on the skins (FoS) had lower ester and volatile thiol concentrations than the control wines (with no skin contact) and limited skin contact wines. Sensory attributes linked to the FoS wines included aromas of dried fruit, dried grass and a vegetative character, with an increased sour and bitter taste and astringent mouthfeel. In contrast, the wines that were produced with limited skin contact (12 hours) retained their tropical fruity aromas better than the FoS wines. Limited skin contact seemed to have had a less harsh effect on the taste and mouthfeel than the FoS wines. A consumer study was done to establish a Generation Y consumer group’s (18-35 years) preference for the different treated wines. Overall, the naturally fermented wines, which were described as having a strong tropical fruit character, were preferred. The FoS wines were generally disliked by the consumers. Results obtained from the three sensory analysis methods, respectively DA, PM and FC, were similar, thereby confirming the suitability of the rapid methods PM and FC, to extract qualitative information from the sensory profiling of white wine. The results of this study made a significant contribution towards validation of rapid sensory methods for wine evaluation, which are particularly valuable in the context of sustainability and technology transfer to research and industry alike. The knowledge gained on the chemical profiles of SA Chenin blanc is novel and this is one of the first reports on the volatile thiol content of SA Chenin blanc wine.

AFRIKAANSE OPSOMMING: Produsente van Suid-Afrikaanse (SA) droë en semi-droë Chenin blanc tafelwyne eksperimenteer tans met wynmaaktegnieke om die oorwegend vrugtige style van hierdie genre te varieer. ‘n Belangrike fase van wynstylontwikkeling is sensoriese profilering van die produkte met gepaardgaande verbruikersaanvaardingstoetse, voordat die wyne op industriële skaal geproduseer word. Met dié bogenoemde doelwitte in gedagte, was hierdie studie in vennootskap met twee kommersiële SA wynkelders gedoen. Die hooffokus van die studie was om die invloed van twee wynmaaktegnieke, onderskeidelik druifdopkontak en natuurlike fermentasie, op die sensoriese profiele van eksperimenteel geproduseerde Chenin blanc wyne te ondersoek. Resultate wat met beskrywende sensoriese analise (DA) van die wyne verkry is, is vergelyk met dié wat deur twee vinniger sensoriese profileringsmetodes metodes, naamlik projektiewe kartering (PM) en frekwensie van kenmerkaanhaling (FC) verkry is. 'n Verbruikervoorkeurstudie is ook op die wyne gedoen. Ten einde die behandelingseffekte beter te verstaan, is die dominante nie-Saccharomyces giste wat teenwoordig was tydens die natuurlike fermentasie geïdentifiseer met behulp van die polimerasekettingreaksie (PCR), terwyl die vernaamste vlugtige chemiese verbindings geïdentifiseer is met chromatografie en massaspektrometrie. Die sensoriese en chemiese profiele van die natuurlike gefermenteerde wyne was beduidend anders as dié van die geiinokuleerde wyne. PCR analise het sommige giste wat teenwoordig was tydens alkoholies fermentasie geïdentifiseer. In vergelyking met die geiinokuleerde wyne, het die natuurlik gefermenteerde wyne intenser en ryper tropiese vrugtige aromas getoon, met ‘n verhoogde perspesie van soetheid en laer intensiteite van suurheid, bitterheid en vrankheid. Die wyne wat berei is deur fermentasie op die druifdoppe (FoS) het laer konsentrasies van esters en vlugtige swawelverbinding gehad, as die kontrole wyne (geen dopkontak) en beperkte dopkontak wyne. Sensoriese eienskappe gekoppel aan die FoS wyne was geasssosieer met gedroogde vrugte, gedroogde gras en 'n vegetatiewe aroma, met gepaardgaande verhoogde suur en bitter smaakpersepsies en ‘n frank mondgevoel. In teenstelling, het die wyne wat geproduseer is met 'n beperkte dopkontak (12 uur) hul tropiese vrugtige aroma beter behou as die FoS wyne. Beperkte dopkontak het ook ‘n minder negatiewe uitwerking op die smaakpersepies van bitterheid en vrankheid gehad. ‘n Verbruikerstudie is gedoen om 'n groep jong Generasie Y verbruikers (18-35 jaar) se voorkeure vir die verskillende behandelings te bepaal. Oor die algemeen is die natuurlike gefermenteerde wyne, wat beskryf is met 'n sterk tropiese vrugtekarakter verkies, terwyl die groep nie van die FoS wyne gehou het nie. Resultate wat verkry is met drie sensoriese analise metodes, onderskeidelik DA, PM en FC, was soortgelyk en die geskiktheid van die vinniger metodes, PM en FC, om kwalitatiewe inligting van witwyn se sensoriese eienskappe te verkry, is bevestig. Die resultate verkry met hierdie studie maak ‘n beduidende bydrae tot die validering van vinniger sensoriese metodes vir wynevaluering, wat veral waardevol is in die konteks van volhoubaarheid en tegnologieoordrag na navorsing en die industrie. Die nuwe kennis wat in hierdie studie gegenereer is met die chemiese profilering van SA Chenin blanc wyn is baie waardevol en hierdie is een van die eerste narvorsingsprojekte oor die inhoud van vlugtige swawelverbings in SA Chenin blanc wyn.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/96008
This item appears in the following collections: