606 A. Bertrand and A.A. Beloqui
The second is that H 2 S cannot react with ethanal because it is bound to SO 2 in the
bisulphitic combination or to phenolic compounds.
Two experiments were performed to try to determine which of these reactions
was occurring. After macerating the red wine grapes for one day the coloured must
obtained was seeded with yeasts (100 mg/L of LSA). Also, a commercial white
must was seeded with the same dose of yeasts. When fermentation started, 5 mg/L
of H 2 S were added and the analysis was carried out one week after finishing alco-
holic fermentation. In both cases, the formation ofcis-/trans-3,6-dimethyl-1,2,4,5-
tetrathiane and ofcis-/trans-3,5-dimethyl-1,2,4-trithiolane was detected. The mass
spectra are shown in Figs. 10.9 and 10.10. By contrast, in this experimentcis-/trans-
4,7-dimethyl-1,2,3,5,6, pentathiepane and 1,1-ethanedithiol did not appear.
Isomers of these compounds have very similar retention times in these conditions
(Fig. 10.11). With a polar column, thecis-/trans-3,5-dimethyl-1,2,4-trithiolane exit
first, followed bycis-/trans-3,6-dimethyl-1,2,4,5-tetrathiane.
32455964(^7185)
92
124
184
30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
22000
24000
26000
28000
30000
(A)
(B)
m/z-->
Abundance
41
45
59
64
71
81
92
124
184
30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
22000
24000
26000
m/z-->
Abundance
Fig. 10.9Mass spectra ofcis-/trans-3,6-dimethyl-1,2,4,5-tetrathiane