E520 - Aluminium sulphate
What it is and how it is used
Aluminium sulphate is the compound better known as alum, made by dissolving bauxite or aluminium hydroxide in sulphuric acid. Most of the world's production goes to water treatment and papermaking; only a small, tightly restricted fraction is food grade.
In food its function is firming. Aluminium ions cross-link the pectin in plant cell walls, which is why alum has been the traditional crisping agent for pickles for centuries, and why it is used on egg white to stabilise the foam in some products. Its GB authorisation is narrow — egg white — rather than general.
Foods commonly containing it
In Great Britain, egg white products. Historically, and still in some countries, it appears in pickled vegetables as a crisping agent and in some baking powders.
Safety summary
Aluminium sulphate is authorised in Great Britain as E 520, within the group “E 520–523: Aluminium sulphates”, with restricted permitted uses.
The relevant health-based reference value is for aluminium rather than for sulphate. EFSA established a tolerable weekly intake of 1 mg aluminium per kg of body weight per week in 2008 — down from the earlier JECFA provisional figure of 7 mg — and carried it forward in its 2018 re-evaluation of E 520–523 and E 541. A weekly rather than daily value is used because aluminium accumulates in the body.
Known concerns
Aluminium reaches the diet from several directions at once — this and related additives, cookware, foil, drinking water treatment and some medicines. EFSA's 2018 assessment put mean exposure from E 520–523 and E 541 at up to 0.21 mg/kg bw/day in children. Because the reference value is weekly and the metal accumulates, the additive contribution is judged against a cumulative total rather than in isolation.