It is a salt of tartaric acid, which also acts as an acidity regulator because its crystals have the capacity to retain water, and partly react to it.
It is an acid which is found naturally in fruits, particularly grapes. It can be produced industrially by chemical synthesis and is found as a white powder. This food additive is used in food industry as an antioxidant, acidity regulator, emulsifier, stabilizer etc.
It is found in many foods. It is used according to the specified amounts in the recipes for products based on chocolate and cocoa, in jams, jellies, marmalades, fruit juices and nectars or juice concentrates and nectars, gum etc.
It is not allowed in foods for infants and young children.
E337 – Potassium Sodium Tartrate side effects
The acceptable daily intake for human consumption is up to 30 mg/kg. High doses cause gastrointestinal disorders, with laxative and diuretic effect. It is however much less toxic than E 334 tartaric acid.
Given the stated dose (rather small), we can conclude that this food additive is not very safe and so we recommend that you avoid foods containing it.