Wine Chemistry and Biochemistry

264 R. Baumes

is generally associated with other volatile sulfur compounds eliciting such off-odors

(Park et al. 1994).

In contrast, levels of DMS much higher than its perception threshold were

reported to be specifically produced without generating off-odors in many bottled

wines during aging, and levels increased with time and temperature (Marais 1979;

De Mora et al. 1986, 1993; Anocibar Beloqui 1998; Goto and Takamuto 1987;

S ́egurel et al. 2004; Dagan 2006). Thus, high levels of DMS would contribute

positively to the bottled bouquet in aged premium red wines and late harvest

wines (Anocibar-Beloqui et al. 1996; Anocibar-Beloqui et al. 1998; Dagan 2006;

Du Plessis and Loubser 1974; Spedding and Raut 1982). Furthermore, De Mora

et al. (1987) reported the enhancement of fruity notes of Cabernet Sauvignon red

wines by DMS, which was later confirmed in other samples (S ́egurel et al. 2004;

Escudero et al. 2007). However, sensorial data are not available for wines from a lot

of cultivars, and the sensorial interactions of DMS with other aroma compounds are

still unknown.

The potential DMS in wine, susceptible to be released during wine aging, was

evaluated by an indirect method using achemical treatment to degrade wine DMS

precursors into DMS (S ́egurel et al. 2004, 2005). That method showed that such

DMS potential (PDMS) occurred in grape, and that DMS released during wine aging

could not be explained by DMSO, which has long been regarded as the only wine

DMS precursor (De Mora et al. 1986, 1993; S ́egurel et al. 2004, 2005). Then, among

the other possible DMS precursors known in plants (Bezzubov and Gessler 1992;

Howard and Russell 1997), SMM was identified as the major DMS precursor in
grape using MALDI-TOF MS (Fig. 8A.7) (Loscos Deosdad et al. 2007). During

the first steps of winemaking, SMM gets from grape into wine, and it is only when

wine is in stoppered bottle during its storage that DMS become accumulated, as it

is released from SMM by an elimination reaction (Hoffmann degradation), a slow

chemical process in usual wine storage conditions (S ́egurel et al. 2004, 2005). Thus,

the differences in DMS levels observed between wines depend primarily on the

PDMS levels at bottling, then on the conditionsof storage, particularly on tempera-

ture (Marais 1979).

PDMS measured in musts from grapes of different cultivars showed that all the

samples analyzed contained DMS precursors,with high variation between cultivars,

from levels lower than the perception threshold in some Grenache samples up to 4.5

mg/L in some Petit Manseng samples, and high variation between samples of the

same cultivar (S ́egurel 2005; Dagan 2006). Thus, grape PDMS is not only under

genetic control, but it is also dependent on the several factors which define the

“terroir”, and it increases dramatically with over-ripening (Dagan 2006).

CH 3

S

CH 3

CH CH 2 CH 2

HO 2 C

H 2 N

Fig. 8A.7S-Methylmethionine, precursor of DMS