Sodium hydrogen diacetate is the sodium salt of acetic acid, used in food as a preservative and firming agent. It inhibits mould and bacterial growth, particularly in baked goods where it extends shelf life without affecting flavour at permitted levels, and its acetate component firms the texture of processed vegetables and other foods. As a buffered form of vinegar’s active acid, it delivers antimicrobial power in a stable, easy-handling powder. It is one of the quieter preservatives on the label, effective against the rope-forming bacteria that spoil bread and against moulds that attack packaged foods. Like all food preservatives it is used within strict legal limits, a small dose doing the work of keeping food safe longer.