Scheurebe wines

Fig. 11.1 Descriptive analysis of two Scheurebe wines made from the same juice but fermented by two different commercial yeast strains (ten judges x two replications) [58]...

Guth (1997) demonstrated the major olfactory impact of 4MSP in Scheurebe wines, which may contain as much as 400 ng/L. 

Recently, AEDA and SHA-0 yielded 41 and 45 odor active compounds for Scheurebe and Gewurztraminer wines, respectively (P). Ethyl 2-methylbutyrate, ethyl isobutyrate, 2-phenylethanol, 3-methylbutanol, 3-hydroxy-4,5-dimethyl-2(5H)-furanone, 3-ethylphenol and one unknown compound, named wine lactone, showed high flavor dilution (FD)- factors (Table I) in Gewurztraminer and Scheurebe wines. 4-Mercapto-4-methylpentan-2-one belongs to the most potent odorants only in the variety Scheurebe whereas cis-rose oxide was perceived only in Gewurztraminer (Table I). 4-Mercapto-4-methylpentan-2-one was identified for the first time in Sauvignon blanc wines (JO). The unknown compound with coconut, woody and sweet odor quality, which has not yet been detected in wine or a food, was identified as 3a,4,5,7a-tetrahydro-3,6-dimethylbenzofuran-2(3H)-one (wine lactone) (JJ). 

To estimate the sensory contribution of the 42 odorants to the overall flavor of the wine samples, their OAV s were calculated (Table II). To take into account the influence of ethanol, the odor threshold values of wine odorants were determined in a mixture of water/ethanol (9+1, w/w) and were used to calculate the OAV s for each compound. According to the results in Table A, 4-mercapto-4-methylpentan-2-one, ethyl octanoate, ethyl hexanoate, 3-methylbutyl acetate, ethyl isobutyrate, (E)-fi-damascenone, linalool, cis rose oxide and wine lactone showed the highest OAV s in the Scheurebe wine. With exception of 4-mercapto-4-methylpentan-2-one the above mentioned odorants also showed the highest OAV s in Gewurztraminer wine. Differences in the OAV s of ethyl octanoate, ethyl hexanoate, 3-methylbutyl acetate and ethyl isobutyrate between the two varieties are probably caused by differences in the maturity of the fruit at harvest and/or by the fermentation process. 

Table IV. Concentrations and taste values (> 0.1) of compounds in Gewiirz-traminer and Scheurebe wines...

Typical Scheurebe wines are characterized by a jfruity aroma, which is described as redcurrant-like, often with a grapefruit note. In 1995 Darriet et al. identified 4-mercapto-4-methylpentan-2-one (MMP), responsible for the distinctive odor of box tree and cat urine (7). The perception threshold of this compound in wine has been reported to be very low (3 ng/1). Recent studies by Guth and coworkers (2) showed that MMP also significaiitly influences the aroma of Scheurebe wines. 

The aim of the present study was the isolation and identification of new flavor compounds from Scheurebe wine at trace level. For enrichment purposes preparative multidimensional gas chromatography (MDGC) was used. The structure elucidation of the isolated compounds was on the basis of spectroscopic methods (NMR, GC-FTIR, GC-MS) and synthesis as well. The sensory properties of the isolated compounds were correlated with the typical aroma profile of Scheurebe wines. 

Sample preparation. For the study of trace compounds we used two different sample preparation procedures SPI and SPII for wine no. 1 and wine no. 2, respectively. The first flavor extract SP I was obtained by liquid-liquid extraction with fluorochloromethane and dichloromethane (9+1) from 45 L Scheurebe wine. For further analysis a portion of 1/3 was used. After separation on silica gel (pentane/diethyl ether) 6 fractions were analyzed. For the second flavor extract SP II we started from 200 L wine stripping off volatile compounds with vapour in a spinning cone column (SCC) system (5). The condensate was sequentially collected in two main portions of 8 and 2 L, respectively. The first condensate was discarded. The second condensate (2 L) was subjected to liquid-liquid extration with fluorochloromethane and dichloromethane (9+1). After separation on silica gel (pentane/diethyl ether) using medium pressure chromatography (MPLC) 4 fractions were analyzed. 

Methionol derivatives. Methionol, 3-(methylthio)-l-propanol, a well known S-compound in white and red wines was first identified by Muller et al. (77). The biosynthesis of methionol starts from methionine following the Ehrlich-mechanism 18). The sensory properties of methionol are descibed as raw potatoes (77). Not only methionol, but also succinic acid is a normal by-product of alcoholic fermentation. Our studies on volatile compounds in Scheurebe wines revealed for the first time the presence of succinic acid ethyl methionyl ester (5). This compound is characterized... 

Figure 2. GC-MS analysis of thiocarbonic acid O, S-dimethyl ester (4) in Scheurebe wine extract (SP II). GC column DB-Wax...

A dilution experiment by SHA-0 indicated acetaldehyde, ethyl acetate, dimethylsulfide and dimethyltrisulfide as further potent odorants in Scheurebe and Gewurztraminer wines. AEDA and SHA-0 yielded the same assessment of 4-mercapto-4-methylpentan-2-one and cis-rose oxide, which are responsible for the odor difference of the two varieties, investigated in this study. It should be mentioned that only one sample of each variety was analyzed and for more generality further investigations are necessary. 

To establish exactly the flavor differences between Scheurebe and Gewurztraminer wines, it is therefore necessary to quantify the levels of recognized odorants and to calculate the odor activity values (OAV s). According to Rothe and Thomas (75) the OAV is defined as ratio of concentration to odor threshold value of the compound. 

Calculation of OAV s indicated that significant differences in odor profiles of both varieties, investigated in this study, were mainly caused by cis-rose oxide in Gewurztraminer and 4-mercapto-4-methylpentan-2-one in Scheurebe. Investigations about the formation of 4-mercapto-4-methylpentan-2-one in wine were performed by Tominaga et al. (22), who found that the compound was released from an odorless must extract by a cysteine-fl-lyase. The authors suggested that the compound was bound in form of S-(4-methylpentan-2-one)-l-cysteine in grape must. 

Table II. Concentrations and Odor Activity Values (OAV s > 10) of Potent Odorants of Scheurebe and Gewurztraminer Wines...

Wines. Two different wines vitis vinifera L. cv. Scheurebe from the Pfalz area in Germany were analyzed. Scheurebe is a cross breeding of the two cultivars Riesling and Silvaner. Wine no. 1 Scheurebe Qualitatswein b. A. from 1992 provided from a cooperative winery. Wine no. 2 Qualitatswein b. A. from 1995, was obtained from a small winery. 

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