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.

Thesis (MAgricAdmin (Agricultural Economics))--University of Stellenbosch, 2005. / The wine industry is one of the oldest commercial activities in South Africa. The South African wine grape industry annually produces more than a million tonnes of grapes, making the country the ninth largest producer in the world. The total area under wine grape production is divided into eight regions for administrative purposes. These boundaries are a legacy of the era of controlled marketing and there is continued meaningfulness of having various classifications such as ‘wine of origin’ scheme. The purpose of this study is to identify the factors that determine the producers’ choice of wine grape cultivars in the wine regions in South Africa. Time series data for the period 1990-2003 were used to estimate the parameters of linear regression models. Two equations for each wine grape cultivar in each region were postulated and estimated using Ordinary Least Squares as applied with Eviews. Further, a stepwise regression as applied in STATISTICA was used to eliminate the parameters that were not statistically significant at five percent significant level. In identifying the factors that determine the choice of wine grape cultivars in the regions, the results showed that each wine grape cultivar in each region has its own factors influencing the producers’ choice of that specific wine grape cultivar. Same wine grape cultivars in different regions similarly have its own factors determining the producers’ choice. The implication of this is that there are differences in terms of the requirements and types of crops and wine grape cultivars grown in each region. However, the most important result that emerged with regular frequency is that, the factors determining the producers’ choice of a specific wine grape cultivar for each region is price of other wine grape cultivars and competitive products in that wine region. The price of specific wine grape cultivars only had an influence on few wine grape cultivars. The implication is that the producers in South Africa appears to consider the prices of other wine grape cultivars and competitive products before making a choice of whether to plant or uproot a specific wine grape cultivar more than the price of the specific wine grape cultivar. This supports the theory that farm prices play a key role in allocating resources and in rewarding efficient producers.