Wine Chemistry and Biochemistry

10 Aromatic Spoilage of Wines by Raw Materials and Enological Products 605

1-hydroxyethanethiol

ethanal

1,1-ethanedithiol

cis/trans-4,7-dimethyl-1,2,3,5,6-pentathiepane

cis/trans-3,6-dimethyl-1,2,4,5-tetrathiane

bis(1-sulfanylethyl)sulfure cis/trans-3,5-dimethyl-1,2,4trithiolane

+2CH 3 2CH 3

[O]

S S

S

S

S

H 3 C

H 3 C

H 3 C

H 2 S

CH 3

CH 3

CH 3

CH 3

CH 3

S

SS

S

C

O

H

CH

OH

SH

CH

SH

SH

S

S

S

C

S

C

SH SH

H H

• H 2 S

2 H 2 S

[O]

[O]

Fig. 10.8Sulphur compounds formed in the reaction of H 2 S with ethanal (according to different
authors)

These compounds, produced in the reaction of H 2 S and ethanal, have been

detected in a synthetic solution and in a white wine by Rauhut and Dittrich (1993).

These authors made H 2 S at concentrations from 1 to 5 mg/L react with ethanal at

variables concentrations from 100 to 500 mg/L. This reaction producescis-/trans-

3,6-dimethyl-1,2,4,5-tetrathiane, thecis-/trans-4,7-dimethyl-1,2,3,5,6-pentathiepane

and thecis-/trans-3,5-dimethyl-1,2,4-trithiolane and the precursor of these com-

pounds, 1,1-ethanedithiol. However, the same reaction with copper does not prevent

formation of these compounds. In contrast, the reaction reported by some authors

between H 2 S and ethanal to form ethanethiol, does not take place.

We did not detect any of the reaction products between H 2 S and ethanal in any

of the red wines studied, not even in the wines with a strong concentration of H 2 S.

We carried out some experiments in an attempt to explain this phenomenon.

The first consisted in carrying out the reaction in a synthetic solution, as Rauhut

and Dittrich (1993) has done previously and, indeed, we too detected the sulphur

compounds described by the authors.

Then3mgofH 2 S were added to a red wine containing 75 mg/L of ethanal

(a higher value than that normally detected in red wines). The dose of free SO 2

remained at 30 mg/L, but after 10 days none of the compounds described were

detected. There are several possible reasons for this. The first is that H 2 S reacts

with other red wine compounds, such as phenolic compounds (De Freitas 1995).