Thesis (MSc)--Stellenbosch University, 2014. / 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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/96008 |
| Date | 12 1900 |
| Creators | Weightman, Jayne |
| Contributors | Nieuwoudt, Helene, Setati, M. E., Stellenbosch University. Faculty of AgriSciences. Dept. of Institute for Wine Biotechnology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 166 p. : ill. |
| Rights | Stellenbosch University |
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