Wine Chemistry and Biochemistry

284 D. Dubourdieu and T. Tominaga

Blanc” (Galet 1968). Benzenemethanethiol (XIII), a volatile thiol with a strong

empyreumatic odor, described as “flint”, was identified in boxwood, as well as red

and whiteVitis viniferaL. wines. Its perception threshold is on the order of 0.3 ng/L

(Tominaga et al. 2003b). This volatile thiol has been assayed in several white Sauvi-

gnon blanc, S ́emillon, and Chardonnay wines from various French appellations, as

well as in a few red Bordeaux wines made from Cabernet Sauvignon and Merlot.

The benzenemethanethiol content of the Chardonnay wines, irrespective of their

provenance, was two- or threefold higher than that of wines made from the other

grape varieties studied (Fig. 8B.2). Sauvignon blanc wines from the Loire Val-

ley and Bordeaux, as well as S ́emillon from Bordeaux, had comparable benzen-

emethanethiol concentrations (10–15 ng/L). The red Bordeaux wines analyzed,

from various different vintages and appellations, had benzenemethanethiol concen-

trations around 10 ng/L.

The composition of the odoriferous compounds responsible for hints of roasting

coffee in wines fermented in new barrels was unknown until quite recently. Furan

aldehydes, particularly furfural, smell toasty, but their perception threshold is much

higher than the concentrations found in wine. Their olfactory impact is, therefore,

negligible. Research by Tominaga et al. (2000b) demonstrated that the key com-

pound in the roasting coffee aroma of barrel-aged wines was 2-furanemethanethiol

(2FM) (IV), an extremely odoriferous volatile thiol (perception threshold: 0.4 ng/L).

This molecule was first identified in roasted coffee, as early as 1926 (Reichstein and

Staudinger 1926)

The mechanisms responsible for 2FM formation in wine have not yet been
completely elucidated. During alcoholic fermentation of white wines in barrel,

it is produced by bio-conversion of furfural released by the oak, via the yeasts’

sulfur metabolism (Blanchard et al. 2001). Only traces of this volatile thiol are

found in white wines fermented in stainless-steel vats. In red Bordeaux wines,

0

5

10

15

20

25

30

35

40

45

Chardonnay

1999

Limoux

Chardonnay

1999

Bourgogne

Sauvignon

1999

Sauvignon

2000

Sauvignon

2000

Semillon

2000

Cabernet

Merlot

n = (^3) n = 7
n = 8
n = (^12) n = 9 n^ =^4
n = 6
ng/L
Sancerre Bordeaux
Fig. 8B.2Concentrations (ng/L) of benzenemethanethiol in some white and red wines made from
differentVitis viniferagrape varieties (Tominaga et al. 2003)