Sulphur dioxide
Sulphur dioxide (SO₂) is a colourless gas widely used in winemaking for its preservative and antimicrobial properties. In wine, it acts primarily as an antioxidant and stabilising agent, protecting against spoilage and oxidation while helping to preserve freshness and longevity.[1]
Background
The use of sulphur in wine dates back to antiquity, with evidence of sulphur candles being burned inside amphorae and barrels to sanitise containers.[2] Its systematic application in winemaking developed from the Middle Ages onwards, becoming standard practice by the 19th century.
Today, the use of sulphur dioxide is regulated internationally by the OIV and by national authorities, which impose maximum allowable concentrations depending on wine style and residual sugar levels.[3] Despite common misconceptions, all wines naturally contain some sulphur compounds as a by-product of fermentation, even if no SO₂ is added. Consumer sensitivity to sulphites has driven increasing interest in low-sulphur and “natural” wines.
Characteristics
Sulphur dioxide serves as both an antioxidant and antimicrobial agent. It prevents oxidation by binding with compounds such as acetaldehyde and protects against microbial spoilage by inhibiting yeasts and bacteria.[4]
Winemakers distinguish between “free” SO₂, which is active and protective, and “bound” SO₂, which has reacted with other compounds and is no longer effective. Maintaining an appropriate balance between the two is essential for wine stability.[5]
In sensory terms, sulphur dioxide can sometimes be detected at high concentrations as a pungent, acrid smell reminiscent of a struck match. Labelling regulations in most wine-producing countries require wines containing more than 10 mg/L of sulphites to carry the statement “contains sulphites”.
Use in winemaking
Sulphur dioxide may be added at several stages of production: during grape harvest, at crushing, before or after fermentation, during maturation, and prior to bottling.[6] Its addition helps stabilise colour, control microbial populations, and extend the wine’s ageing potential.
Regulatory limits vary but typically range from 150 mg/L for dry red wines to 400 mg/L for sweet wines with high residual sugar.[7] Excessive use, however, may mute aromas and is increasingly avoided in modern enology. Alternatives such as inert gas blanketing, sterile filtration, and the use of natural antioxidants (e.g. ascorbic acid) have been explored, but SO₂ remains the most effective and widely used preservative.
See also
References
- ↑ Robinson (ed.), The Oxford Companion to Wine, Oxford University Press, 2015.
- ↑ McGovern, Ancient Wine: The Search for the Origins of Viniculture, Princeton University Press, 2003.
- ↑ OIV, “Use of sulphur dioxide in winemaking”, www.oiv.int.
- ↑ Ribéreau-Gayon, Dubourdieu, Donèche & Lonvaud, Handbook of Enology, Vol. 1, Wiley, 2006.
- ↑ Jackson, Wine Science: Principles and Applications, Academic Press, 2020.
- ↑ Boulton, Singleton, Bisson & Kunkee, Principles and Practices of Winemaking, Springer, 1999.
- ↑ OIV, “Use of sulphur dioxide in winemaking”, www.oiv.int.