As mentioned in our introduction to natural wine, sulfites (or SO2) may be added to act as a preservative, or in an attempt to ensure consistent qualities during exportation. Sulfur dioxide has been used as a part of winemaking since ancient Roman times. They used it to sanitize barrels and equipment rather than preserve wine, however.
There is little if any factual evidence to show sulfites are harmful to your health, though some people believe it gives them headaches or allergic reactions. It’s hard to pinpoint exactly what in the wine is the trigger, as label regulations are not nearly as strict as in the food industry.
For many people, it’s purely a matter of taste. This method of intervention, like fining or filtration, doesn’t allow the wine freedom to develop its full character and can stunt aging in the bottle. This is one reason why natural wines are ready to drink earlier than many traditional wines.
Though it is possible, sulfite-free wines are incredibly rare as sulfites occur naturally from yeasts during fermentation. Generally, anything up to about 20 mg/l is accepted in the natural wine world as “low-sulfite”. Standards do vary internationally, but under European Union law, anything containing more than 10 mg/l must include “contains sulfites” on the label.