282 D. Dubourdieu and T. Tominaga
Ta b l e 8 B. 7Distribution of the two enantiomers of 3SH and 3SHA in dry white and sweet wines
made from different grape varieties in different vintages. (Tominaga et al., 2006)
Vintages Wine type Varieties 3SH (R:S) 3SHA (R:S)
Dry Sauvignon 1 45:55 30:70
Dry Sauvignon 2 44:56 32:68
2004 Dry Semillon 1 49:52 28:72
Sweet Semillon 1 24:76 n.d.
Sweet Semillon 2 34:66 n.d.
Dry Sauvignon 1 51:49 n.d.
Dry Sauvignon 2 57:43 n.d.
Dry Sauvignon 3 55:45 27:73
Dry Semillon 1 52:48 n.d.
2005 Dry Semillon 2 51:49 n.d.
Dry Semillon 3 52:48 n.d.
Sweet Sauvignon 34:66 n.d.
Sweet Semillon 1 33:67 n.d.
Sweet Semillon 2 32:68 n.d.
n.d.: not detected
the 2005 vintage (Table 8B.7). However, in sweet S ́emillon wines made from botry-
tized grapes, the ratio of the two enantiomers of 3SH (30:70) is very different from
that in dry wines, irrespective of the vintage (Table 8B.7) (Tominaga et al. 2006).
The ratio of the two enantiomers of 3SHA was only determined in dry wines as
this compound is never present in sweet, botrytized wines. The distribution of the
two 3SHA enantiomers (R:S) in dry wines was approximately 30:70 for both grape
varieties studied (Table 8B.7).
The yeast strain used for fermentation had no impact on the enantiomer distribu-
tion of these volatile thiols. 3SHA is generally considered to be formed by esterifica-
tion of 3SH by yeast during alcoholic fermentation. The esterase or lipase involved
probably acetylates 3SH with a certain enantioselectivity. In contrast, the enan-
tiomer distribution of 3SH in wine made from botrytized grapes(Botrytis cinerea)is
25:75 in favor of the S form, which has also been found in botrytized must (Thibon
et al. 2007, 2008a).
The perception thresholds of the R and S forms of 3SH are very similar. However
these two enantiomers have different aromas that were significantly distinguished in
the triangular tasting test. The R form’s aroma is reminiscent of grapefruit, while the
S form smells of passion fruit. The perception threshold of the S form of 3SHA is
approximately four times lower than that of the R form. Furthermore, the S enan-
tiomer is three times more abundant in wine than the R form. These two enantiomers
have different aromas: the R form is more herbaceous, evocative of boxwood, while
the S form is fruitier, reminiscent of passion fruit. These differences in aroma are in
agreement with the findings of Weber et al. (1992). Significantly, these experiments
demonstrated that the enantiomer distribution of thiols such as 3SH and 3SHA
must be taken into account in assessing the olfactory impact of these compounds
in wine (Table 8B.8).