Thesis (MSc Food Sc )--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Highly valued Sauvignon blanc wines, with the distinctive cultivar-typical aromas,
reminiscent of grassy, green pepper or asparagus-like, are produced in some South
African regions. Quite often, however, neutral and sulphur-like, low quality
Sauvignon blanc wines are produced and this phenomenon is of great concern to
wine producers and consumers, and affects our competition on overseas markets,
negatively.
The aim of this study was to investigate the effect of region, ascorbic acid/S02
treatments and yeast strain on Sauvignon blanc wine aroma and quality. Wines were
produced from grapes obtained from the warmer Robertson and the relatively cooler
Stellenbosch regions (1998 season). The juices were treated with different
combinations of ascorbic acid/S02 treatments [commercially available ascorbic
acid/meta preparate, S02 (control), pure ascorbic acid/S02] and Saccharomyces
cerevisiae yeast strains (Vin 13, VL3C, NT 116). The wines were analysed for
esters, higher alcohols, monoterpenes and 2-methoxy-3-isobutylpyrazine (ibMP).
The wines were also sensorially evaluated for wine aroma intensities (fruity/ester,
sulphur-like, grassy/green pepper) and overall quality. Additionally, the synergistic
action of ibMP and the sulphur-containing component, 4-mercapto-4-methylpentan-2-
one (MMP), considered to be the most important impact components of Sauvignon
blanc, was studied. The two components were added, separately and in
combinations at increasing concentrations, to different media. The nuances
perceived, varied from dusty, grassy to green pepper for ibMP and from guava,
sulphur-like to cat urine or "conifer" for MMP.
Significant differences were observed between the wines treated with the different
combinations of ascorbic acid/S02 treatments and fermented with different yeast
strains, irrespective of region. The highest quality, cultivar-typical Sauvignon blanc
wines were produced from the pure ascorbic acid/S02 treatment in combination with
yeast strains Vin 13 and NT 116. This coincided with high ester and low higher
alcohol concentrations, which did not overpower the typical Sauvignon blanc
character. The treatments had, in some cases, a significant effect on monoterpene
levels, but it was concluded that these differences were not big enough to affect wine
quality. Levels of ibMP were too low and could not be reliably measured. Low quality wines, with prominent, undesirable sulphur-like aromas, were produced from
juices, treated with the commercially available ascorbic acid/meta preparate and the
French yeast strain, VL3C.
Techniques, followed to identify the aroma components causing the sulphur-like offflavours,
as MMP or as other sulphur-containing components, were gas
chromatography/mass spectrometry, solid phase microextraction and sniffing.
However, these tests were not successful and studies to identify these off-flavours
should be continued.
It was succeeded in this study to produce Sauvignon blanc wines without the
undesirable, sulphur-like aromas. Although this investigation showed that a newly
developed, commercially available ascorbic acid/meta preparate did not yield any
sulphur-like off-flavours, quite often Sauvignon blanc wines with such off-flavours are
still produced. Further research is needed to clarify this phenomenon. / AFRIKAANSE OPSOMMING: Hoë kwaliteit Sauvignon blanc wyne, met kenmerkende kultivar-tipiese, gras-,
groenrissie- of aspersie-agtige aromas, word in sekere streke van Suid Afrika
geproduseer. Die gereelde produksie van neutrale, en swawelagtige lae kwaliteit
Sauvignon blanc wyne, wek egter nie net groot kommer by wynprodusente en
verbruikers nie, maar het ook 'n negatiewe impak op kompetisie met oorsese markte.
Die doel van hierdie studie was dus om die effek van streek, askorbiensuur/Sóbehandelings
en gisras op Sauvignon blanc wynaroma en kwaliteit vas te stel. Wyne
is berei met druiwe wat verkry is van die warmer Roberston en relatief koeler
Stellenbosch streke (1998 seisoen). Verskillende kombinasies askorbiensuur/So,
behandelings [kommersieel-beskikbare askorbiensuur/meta preparaat, S02
(kontrole), suiwer askorbiensuur/So-l en Saccharomyces cerevisiae gisrasse (Vin
13, VL3C, NT 116) is gebruik tydens die wynbereidingsproses. Spesifieke ester-,
hoër alkohol-, monoterpeen- en 2-metoksi-3-isobutiel metoksipirasienkonsentrasies
(ibMP) is in die wyne bepaal. Die wyne is ook sensories vir wynaroma intensiteite
(vrugtig/ester, swaweiagtig, gras/groenrissie-agtig) en algehele kwaliteit geëvalueer.
Die sinergistiese aksie van ibMP en die swawelbevattende komponent, 4-merkapto-
4-metielpenta-2-oon (MMP), wat beskou word as die belangrikste impakkomponente
in Sauvignon blanc, is addisioneel bestudeer. Hierdie komponente is in toenemende
konsentrasies, individueel en in kombinasies, tot verskillende media gevoeg. Die
nuanses wat waargeneem is, het van stowwerig, gras-, groenrissie-agtig vir ibMP, tot
koejawelagtig, swaweiagtig, katurine, konifeer vir MMP, gevarieer.
Ongeag streke, is betekenisvolle verskille tussen die wyne wat berei is met die
verskillende kombinasies van askorbiensuur/So- behandelings en gisrasse,
waargeneem. Hoër kwaliteit, kultivar-tipiese Sauvignon blanc wyne is berei met
suiwer askorbiensuur/So- in kombinasie met gisras Vin 13 of NT 116. Alhoewel die
hoë ester- en lae hoër alkohol- konsentrasies, hierdie resultate bevestig het, is die
tipiese Sauvignon blanc karakter nie hierdeur oorheers nie. Sommige behandelings
het wel 'n betekenisvolle invloed of monoterpeenkonsentrasies gehad het, maar was
te min om 'n effek op wynkwaliteit uit te oefen nie. Die konsentrasievlakke van ibMP swawelagtige aromas, het egter voorgekom in wyne wat met die kommersieelbeskikbare
askorbiensuur/meta preparaat en die Franse gisras, VL3C, berei is.
Verskeie tegnieke soos gaschromatografie/massa spektrometrie, soliede fase mikroekstraksie
en "sniffing", is gebruik om die komponent, MMP, wat moontlik
verantwoordelik vir hierdie ongewensde swawelagtige wangeure was, te identifiseer.
Die identifikasie hiervan was egter onsuksesvol, en verdere studies is nodig om die
komponent(e) verantwoordelik vir hierdie wangeure, te identifiseer.
Die suksesvolle produksie van Sauvignon blanc, sonder ongewensde swaweiagtig
aromas, was wel moontlik. Alhoewel hierdie studie ook duidelik getoon het dat daar
geen swawelagtige wangeure in die wyne wat met die nuut ontwikkelde,
kommersieel-beskikbare askorbiensuur/meta preparaat berei was, voorgekom het
nie, vind die produksie van Sauvignon blanc wyne met van hierdie wangeure nog
steeds plaas. Verdere navorsing rakende hierdie aspek is nodig.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51968 |
| Date | 12 1900 |
| Creators | Swart, Ewarda |
| Contributors | Marais, J., Britz, T. J., Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 126 p. : ill. |
| Rights | Stellenbosch University |
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