Sulphites
Sulphur-based compounds (primarily sulphur dioxide, SO₂) used in winemaking as an antioxidant and antimicrobial preservative; required to be declared on labels in most markets.
In depth
Sulphites have been used in winemaking for centuries — burning sulphur candles in barrels is one of the oldest preservation techniques. In modern winemaking, SO₂ is added at harvest, during fermentation, and at bottling to protect wine from oxidation and unwanted microbial activity.
SO₂ exists in two forms in wine: free SO₂ (active and protective) and bound SO₂ (combined with sugars and other compounds, largely inactive). Winemakers monitor free SO₂ levels carefully; too little leaves wine unprotected, too much creates a harsh, sulphurous off-aroma detectable as struck match or burnt rubber.
All wines contain sulphites to some degree — even "no added sulphur" wines have naturally occurring sulphites produced by yeast during fermentation. Sulphites are a legal requirement to declare on labels in the EU, USA, and Australia for wines containing more than 10mg/L SO₂. They are a known allergen for a small proportion of the population, particularly those with sulphite sensitivity or asthma.
Sulphites are distinct from sulphides (reduction off-faults such as hydrogen sulphide), a common student confusion.
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Frequently asked questions
- Are sulphites the same as sulfur dioxide?
- Sulphites is the broader term for sulphur-based compounds; sulphur dioxide (SO₂) is the most important of these in winemaking. The terms are often used interchangeably on wine labels. The EU requires any wine with more than 10 mg/L total SO₂ to state "contains sulphites" on the label.
- Do natural wines contain sulphites?
- Even wines with no added SO₂ contain small amounts of naturally occurring sulphites, produced by yeast as a by-product of fermentation. "No added sulphites" means no SO₂ was added by the winemaker, but the wine is not entirely sulphite-free.
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Practise questions on this topic
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