A processing aid is a substance used during food manufacture to achieve a technical effect in processing, but which is not intended to remain in the finished product, though unavoidable traces may persist. Examples include antifoaming agents in frying, filtration aids like diatomaceous earth in brewing, enzymes that clarify juices, and release agents on baking trays. The regulatory distinction from food additives matters: because processing aids are not considered ingredients, they generally need not be declared on labels, though they must still be safe and used according to good manufacturing practice. The category creates transparency debates, since consumers eating the product may not know what touched it, from the fining agents in wine to the processing enzymes in bread. Regulators judge each aid on its residues and toxicology rather than its invisibility.