A pack of 20 campden tablets.

Campden Tablets (AKA sodium metabisulphite) is a source of SO2 (sulphite) in wine making. Also used in beer making to treat water. Sulphites remove free chlorine and chloramines from municipal water supplies.

For every 2 L of wine completely crush one tablet. Dissolve in a small amount of cold water and stir thoroughly into wine. For water treatment, 1 tablet treats 75 L (20 gallons). Crush and stir into water. Each tablet weighs 1/2 gram.