What it is
E220 is sulphur dioxide, a gas at room temperature, used both as a preservative and antioxidant. Industrial production from burning sulphur or from desulphurisation of fossil fuels.
Why it matters
Used in wine-making (to inhibit unwanted yeasts), dried fruit (to preserve colour), pickles, salad bars, and as a preservative in many processed foods. Mandatory EU allergen labelling when above 10 ppm.
What to do
Always vegan. The sulphite family (E221–E228) is similarly vegan.