E521: Aluminium sodium sulphate

What is E521?

E521 is aluminium sodium sulphate, also known as sodium alum, a double salt containing aluminium, sodium and sulphate. It is a white crystalline powder that becomes acidic when it reacts with water and heat.

Origin and production

It is produced industrially by combining aluminium sulphate with sodium sulphate and crystallising the product. It is mineral in origin and does not involve plant or animal materials.

Why is it used?

In some countries, notably the United States, sodium aluminium sulphate is a slow-acting acid in 'double-acting' baking powders, releasing carbon dioxide mainly in the oven. It can therefore be found in biscuits, cakes, pizzas, sandwiches and other baked goods and baking mixes; it has also been used as a firming agent.

Vegan, vegetarian and halal

E521 is a mineral salt suitable for vegans and vegetarians. It raises no particular halal or kosher concerns.

Safety and regulation

Aluminium-containing additives have been restricted in the European Union following EFSA's assessment of dietary aluminium, and E521 is now authorised there only for a very narrow range of uses, such as candied fruit and liquid egg white. Its permitted uses therefore differ considerably between jurisdictions.

Common in