Sulphides in wine

Suphides in wine can bring positive aromatic attributes in the form of thiols (3MH, 3MHA and 4MMP most importantly for Sauvignon Blanc) but more widely can bring negative aromatic attributes in the form of hydrogen sulphide, mercaotans, disulphides and dimethyl sulphides.

The negative sulphides are produced as a result of fermentation, either as a result of elemental sulphur from grapes entering the fermentation or excessive H2S production via yeast nitrogen stress as part of the sulphur reduction sequence.

Each sulphide compound has different aromatic charateristics, H2S being rotten egg, mercaptans being cabbage, onion, garlic and disulphides (DEDS and DMDS) showing cooked cabbage, rubber and garlic aromas.

The commonly used technique to remove undesirable sulphides is the addition of copper sulphate which will cause the S molecules to bind to the Cu molecules and precipitate out of solution. Firstly the type of sulphides must be identified via the copper and cadmium test process which also includes an ascorbic acid treatment to reduce disulphides back to mercaptans (formed from mercaptan oxidation) as disulphides cannot be removed via copper but need reduction before treatment. Alternative treatments such as yeast hull products are being more available and are being accepted as non copper alternative treatments.

Ultimately, reduction in always best treated early, either in the ferment stage with sparging to volatilize, N and amino acid additions to the yeast enough N for the SRS loop, or the additional of copper well before bottling to ensure clean, varietal which will be stable once in the bottle under the reductive environment.