What is a processing aid?

A processing aid is a substance used in the food manufacturing or transformation process in order to allow, facilitate or optimize a stage.
Unlike food additives, processing aids can be found in the final product (usually in smaller quantities compared to additives) as their elimination is considered to be technically impossible.
Processing aids are not classified as ingredients so it is not mandatory to indicate them within the list of ingredients of a foodstuff unless it is an allergen or derived from an allergen for which labeling is mandatory.