The effect of region, yeast strain and ascorbic acid on the development of a sulphur-like aroma and on Sauvignon blanc wine quality

[摘要] 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 SouthAfrican regions. Quite often, however, neutral and sulphur-like, low qualitySauvignon blanc wines are produced and this phenomenon is of great concern towine 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/S02treatments and yeast strain on Sauvignon blanc wine aroma and quality. Wines wereproduced from grapes obtained from the warmer Robertson and the relatively coolerStellenbosch regions (1998 season). The juices were treated with differentcombinations of ascorbic acid/S02 treatments [commercially available ascorbicacid/meta preparate, S02 (control), pure ascorbic acid/S02] and Saccharomycescerevisiae yeast strains (Vin 13, VL3C, NT 116). The wines were analysed foresters, 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 synergisticaction of ibMP and the sulphur-containing component, 4-mercapto-4-methylpentan-2-one (MMP), considered to be the most important impact components of Sauvignonblanc, was studied. The two components were added, separately and incombinations at increasing concentrations, to different media. The nuancesperceived, 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 differentcombinations of ascorbic acid/S02 treatments and fermented with different yeaststrains, irrespective of region. The highest quality, cultivar-typical Sauvignon blancwines were produced from the pure ascorbic acid/S02 treatment in combination withyeast strains Vin 13 and NT 116. This coincided with high ester and low higheralcohol concentrations, which did not overpower the typical Sauvignon blanccharacter. The treatments had, in some cases, a significant effect on monoterpenelevels, but it was concluded that these differences were not big enough to affect winequality. Levels of ibMP were too low and could not be reliably measured. Low quality wines, with prominent, undesirable sulphur-like aromas, were produced fromjuices, treated with the commercially available ascorbic acid/meta preparate and theFrench yeast strain, VL3C.Techniques, followed to identify the aroma components causing the sulphur-like offflavours,as MMP or as other sulphur-containing components, were gaschromatography/mass spectrometry, solid phase microextraction and sniffing.However, these tests were not successful and studies to identify these off-flavoursshould be continued.It was succeeded in this study to produce Sauvignon blanc wines without theundesirable, sulphur-like aromas. Although this investigation showed that a newlydeveloped, commercially available ascorbic acid/meta preparate did not yield anysulphur-like off-flavours, quite often Sauvignon blanc wines with such off-flavours arestill produced. Further research is needed to clarify this phenomenon.

[发布机构] Stellenbosch University