Sulphites in wine: why they are added and who should worry

What sulphites are

"Sulphites" is the everyday word for sulphur dioxide (SO2) and related compounds in wine. They are used as preservatives in many foods, not only wine.

Yeast also produces a small amount of sulphites during fermentation. So even a wine with nothing added is rarely completely free of them. Our guide to how wine is made covers fermentation in more detail.

Why winemakers add them

Sulphur dioxide has been used in winemaking for centuries. Burning sulphur inside barrels to keep them clean is an old cellar practice that is still used today. It does two main jobs.

• Antioxidant. It protects wine from oxygen, keeping fruit fresh and colour bright. Without it, many wines would turn brown and flat quickly.
• Antimicrobial. It holds back spoilage bacteria and wild yeast that would otherwise make the wine taste of vinegar or barnyard.

Only part of the SO2 added stays free and active. The rest binds to compounds in the wine and stops protecting it. How much of the free SO2 is in its most active form depends on the wine's pH, so a low-acid wine needs more SO2 for the same protection. This is why Indian winemakers, working with warm-climate grapes that often have lower acidity, watch pH closely. Winemakers usually add SO2 at several points: to grapes or juice at crushing, after fermentation and before bottling. The aim is the smallest amount that protects the wine. Too much gives a burnt match smell and can catch the back of the throat.

How much is in wine

Many countries set legal maximums for sulphites in wine. Under EU rules, for example, dry red wines have a lower limit than dry whites. Sweet wines are allowed more, because sugar left in the wine is food for microbes. India's food safety standards also set limits for wine.

In general:

• Red wines usually contain less sulphite than whites, because tannin gives them some natural protection.
• Sweet wines usually contain the most.
• Organic wines are often allowed less than conventional wines.

Sulphites are also common in other foods and drinks, including some fruit juices, pickles and processed foods. For perspective, many dried fruits such as dried apricots contain more sulphites per gram than wine does.

What "contains sulphites" means

In many countries, including the EU and the US, any wine with more than 10 mg/L of sulphites must say so on the label. Because almost all wines are above that level, the phrase appears on nearly every bottle.

The statement is an allergen warning, similar to warnings for gluten or nuts. It does not mean the wine has an unusually high level. Our guide to reading a wine label covers other label terms.

Who should take care

A small number of people are sensitive to sulphites. Sensitivity is more common among some people with asthma. Reactions can include wheezing or other breathing symptoms. Anyone with a diagnosed sulphite sensitivity or asthma triggered by sulphites should follow their doctor's advice and read labels on food as well as wine.

For most people, sulphites in wine are not a concern. Headaches after red wine are often blamed on sulphites, but red wine usually contains fewer sulphites than white. Other factors are more likely, including alcohol itself, dehydration and drinking more than intended. Drinking water alongside wine and drinking in moderation help.

Low-sulphite and no-added-sulphite wines

Some winemakers, particularly in the natural wine movement, add little or no SO2. These wines can be excellent. They are also more fragile and more prone to oxidation and spoilage.

In India this matters a great deal. Heat speeds up oxidation and microbial growth. A low-sulphite wine that has sat in a hot warehouse can arrive tired or faulty. If you buy these wines, buy from sellers who store wine properly, keep the bottles cool and drink them fresh. Our guide to wine faults describes what can go wrong.

Behind every label is a set of choices about how much protection a wine needs. Winemakers balance sulphite levels against acidity, pH, storage and how long the wine is meant to last. Understanding those choices tells you far more about a wine than the warning on its back label.