Aluminium potassium sulphate

Aluminium potassium sulphate, commonly known as potassium alum or simply alum, is one of the oldest known chemical compounds, used for centuries in food processing, medicine, and industry. In food it has been used as a firming agent for pickles and brined vegetables, as a clarifying agent for beverages, and occasionally as a leavening acid component. Its astringent properties are well recognised and are the basis of its traditional use in food texture management and water treatment.

JECFA most recently assessed aluminium potassium sulphate in 2006 and issued a "not allocated" ADI, consistent with the regulatory approach to aluminium-containing food additives as a class. While potassium alum has a very long history of use, the contemporary understanding of chronic aluminium accumulation and its potential effects on neurological function led to a more conservative regulatory position that acknowledges insufficient data to define a safe daily intake.

Aluminium potassium sulphate is approved in the EU as E522 for specific food applications. Among the aluminium-containing additives, alum may be the form most familiar to consumers from traditional food preparation contexts — it was widely used in home pickling to keep cucumbers crisp and in homemade maraschino cherry preparation. Modern commercial alternatives including calcium chloride (E509) can provide similar firming effects without the aluminium burden, and many consumers and manufacturers now prefer these alternatives. Consumers with a dietary interest in minimising aluminium intake should note that alum-processed pickles are a relevant exposure source.