INS 340 (ii) is dipotassium hydrogen phosphate, often shortened to dipotassium phosphate, and numbered E340(ii) in Europe. INS 340 covers the potassium phosphates: (i) is the acidic potassium dihydrogen phosphate, (ii) this mildly alkaline dipotassium salt, and (iii) tripotassium phosphate. It is the potassium counterpart of disodium phosphate.
It is made by neutralising phosphoric acid with potassium hydroxide or potassium carbonate. Codex lists it as an acidity regulator, emulsifier, emulsifying salt, humectant, sequestrant, stabilizer and thickener, and it is widely used in coffee creamers and processed cheese.
In Cororo Grape Jelly it sits in a long additive list next to citric and tartaric acids and potassium citrate. Together these salts act as a buffer, taking the edge off the acids and holding the acidity steady so the jelly sets and keeps its chewy texture.
