The monosodium salt of tartaric acid, used in food as an acidity regulator and antioxidant synergist, designated E334. It occurs naturally in grapes and wine, where tartaric acid is abundant, and the manufactured salt helps control acidity and stabilise colour in jams, soft drinks, confectionery, and baking powders. Like other tartrates, it is considered safe at permitted levels and is metabolised normally by the body. Its buffering action keeps pH within desired ranges during processing, protecting flavour and preventing undesirable reactions. The additive must be declared on ingredient labels according to local regulations, listed by name or E number.