Step into a museum filled with celebrated paintings and notice the quiet sheen on an old canvas. The clear varnish that shields it does not rob it of colour. On the contrary, it preserves the palette, prevents cracking, and safeguards the painter’s gestures. Sulphites in wine play a similar role. They do not “paint” the vinous canvas. They exist to protect it.

What Are Sulphites in Wine?

In winemaking parlance, “sulphites” is the usual way to refer to dissolved sulphur dioxide. In contact with wine, this compound appears in three forms that depend on pH: the molecular fraction, the bisulphite ion, and the sulphite ion. The molecular fraction delivers the antimicrobial action. The other two protect against oxidation and inhibit undesirable enzymes. In practice, the effectiveness of sulphites comes from the balance between these forms and the right dose at each stage of vinification.

Why Do All Wines Contain Sulphites?

Because wine production naturally generates sulphur dioxide. The chain of events that leads to sulphites is as follows: grapes are pressed to produce must; yeasts ferment the must; this fermentation yields alcohol, carbon dioxide, and sulphur dioxide; the sulphur dioxide reacts with water in the must and, finally, sulphites form. Hence the “contains sulphites” statement on every wine label. There is no such thing as “wine without sulphites”. What does exist are wines with no added sulphites (an option sometimes used in low-intervention wines).

What Do Sulphites Do?

They serve multiple functions. As antioxidants, they preserve colour, aromas, and freshness. As selective antimicrobials, they curb unwanted yeasts and bacteria such as Acetobacter (which produces vinegar). As enzyme inhibitors, they neutralise harmful enzymes such as laccase and tyrosinase. As extraction aids, they promote the release of tannins and anthocyanins from the must, which strengthens the colour and structure of red wines. At present, no other single compound reproduces this choreography of functions with the same precision and predictability.

The Romans were the first to use sulphites in winemaking: perhaps by chance, they found that empty wine vessels stayed fresh (and free of a vinegary smell) after burning sulphur candles inside them. Even today, together with water and citric acid, sulphur dioxide remains one of the safest and most important agents for cellar hygiene.

Do Sulphites in Wine Harm Health?

The evidence is clear: a small fraction of the population is hypersensitive to sulphites (especially people with asthma or allergies). Among other symptoms, sulphites can trigger urticaria (hives), breathing discomfort, and severe or more pronounced reactions. Labelling exists to alert susceptible consumers. Beyond wine, sulphites are also found in dried fruit such as apricots and raisins, in shellfish, in frozen chips, and in many other foods.

What about headaches? Here, the link between sulphites and headaches is much weaker. Headaches are more likely related to so-called biogenic amines (such as tyramine and histamine), to the effects of excessive alcohol intake, or to dehydration.

There is an interesting paradox here: judicious management of sulphites helps reduce the microbial populations that produce the amines associated with headaches. Wines with no added sulphites may, in certain contexts, therefore contribute to headaches.

How Does the Law View Sulphites in Wine?

In the European Union, a sulphites warning is mandatory above a set concentration (more than 10 mg/L of sulphur dioxide). Maximum limits vary by style. For example, dry reds allow lower levels than whites and rosés, while sweet wines permit higher thresholds due to their residual sugar. Recent transparency rules also allow ingredient lists and nutrition information on an e-label via QR code.

How Do Sulphites Contribute to Dão Wines?

Dão is defined by freshness, elegance, and longevity. Its granitic soils, altitude, and marked diurnal range produce wines with vibrant acidity and fine aromatics (discover the Dão region). In reds from Jaen, Alfrocheiro, or Touriga Nacional, sulphites help preserve a firm ruby hue, rein in oxidation that would dry the tannins, and pave the way for harmonious ageing. In Encruzado whites, like the ones from Quinta da Alameda, they protect floral delicacy, silky texture, and a stony, granitic minerality. In the Dão DOC, sulphites do not conceal faults. They allow the voice of the terroir to reach the glass intact.

Are There Viable Alternatives to Sulphites?

There are promising options, such as the use of chitosan in certain contexts. Rigorous hygiene, careful harvesting, and sound oxygen management also matter. Even so, no single alternative matches the versatility of sulphur dioxide for classic styles intended to age. As with the varnish on a famous painting, the best sulphites are those that never draw attention to themselves—yet their absence is felt in the fading of quality.

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Article reviewed by Patrícia Santos, head winemaker at Quinta da Alameda. She holds a degree in Oenology from UTAD (University of Trás-os-Montes and Alto Douro, 2001), and trained under the guidance of Anselmo Mendes. Her experience spans the wine regions of Dão, Bairrada, and Beira Interior, as well as Arribes.

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