E520 - Aluminium sulphate

At a glance

• What it is: an inorganic salt of aluminium and sulphate, also spelled aluminum sulfate.
• E-number: E520; part of the aluminium sulphates group with E521–E523.
• What it does: works mainly as a firming agent to help fruits stay crisp during candying and similar processes.
• Where it shows up: select preserved or decorated fruits (for example, some glacé or candied fruit products).
• Regulations: allowed only for specific uses and at set maximum levels in the EU; made to defined food-grade specifications.
• Safety: overall aluminium intake is controlled; authorities set a tolerable weekly intake for aluminium from all dietary sources.
• Common swaps: calcium-based firming agents like calcium chloride, or texturising gums and alginates.

Why is Aluminium sulphate added to food?

Manufacturers use aluminium sulphate to help fruits hold their shape. In simple terms, it strengthens plant cell walls and pectin so pieces of fruit do not become soft or mushy during processing. In the EU it is authorised as a food additive only for specific uses and at defined maximum levels, rather than as a general-purpose ingredient.¹

Chemically, aluminium sulphate is a hydrated inorganic salt with the general formula Al2(SO4)3·xH2O, where x is the amount of water bound in the crystals.²

What foods contain Aluminium sulphate?

You are most likely to see E520 on the labels of certain preserved fruit products, such as glacé or crystallised fruits and similar decorations. Its use is restricted to the food categories and maximum levels listed in Annex II of the EU food additive regulation.¹

What can replace Aluminium sulphate?

• Calcium salts as firming agents: calcium chloride or calcium hydroxide
• Alginates and related hydrocolloids that help set texture: sodium alginate or calcium alginate
• Acidulants that support pectin gel strength in fruit systems: citric acid

The best substitute depends on the recipe and whether you need crispness, gel strength, or pH control.

How is Aluminium sulphate made?

Food-grade aluminium sulphate is produced industrially and then purified and crystallised to meet the EU’s identity and purity specifications for E520.³ Those specifications describe it as a hydrated salt with defined composition and limits for impurities.³ Its chemical description as Al2(SO4)3·xH2O reflects that it commonly contains bound water in its crystal structure.²

Is Aluminium sulphate safe to eat?

Safety assessments look at aluminium from all dietary sources, not just one additive. The European Food Safety Authority (EFSA) set a tolerable weekly intake (TWI) of 1 mg aluminium per kilogram of body weight per week, covering aluminium from food, water, and additives together.⁴ EFSA also noted that some people, especially young children with high exposures, could exceed this TWI, so limiting avoidable aluminium sources is sensible.⁴

In the EU, E520 may be used only in specific foods and at maximum levels laid down in law, and the substance must meet strict purity criteria.¹³

Does Aluminium sulphate have any benefits?

• Helps preserve texture in delicate fruit pieces during candying or crystallising
• Supports a neat, intact appearance in decorated fruits
• Can reduce losses from softening in certain fruit-processing steps

These are technological benefits in manufacturing; there are no nutritional advantages.

Who should avoid Aluminium sulphate?

• People who are trying to minimise aluminium intake (for example, parents choosing foods for small children) may wish to pick products without aluminium additives when easy alternatives exist.⁴
• Individuals with kidney problems clear aluminium less efficiently and should be cautious about overall aluminium exposure, as advised in toxicological guidance.⁵

If you have specific medical needs, ask a healthcare professional or dietitian for personalised advice.

Myths & facts

• “It’s the same as alum in baking powders.” Not quite. E520 is aluminium sulphate, while “alum” in foods often refers to aluminium potassium sulphate (E522) or aluminium ammonium sulphate, and leavening systems more commonly use other aluminium salts like sodium aluminium phosphate (E541).
• “Sulfates trigger sulfite allergies.” Sulfates (like E520) are chemically different from sulfites such as sulphur dioxide and its salts; sulfite sensitivity does not automatically apply to sulphates.
• “It’s widely used in all processed foods.” No. In the EU, its use is limited to specific foods and levels set in law.¹

Aluminium sulphate in branded foods

You may find E520 on labels of:

• Glacé or cocktail cherries used for baking and desserts
• Candied or crystallised fruit mixes for cake decoration
• Certain preserved fruit pieces for confectionery

Label wording may read “aluminium sulphate,” “aluminum sulfate,” or “E520.” If you want to avoid it, check ingredient lists on candied or decorated fruit products.

References

Footnotes

1. Regulation (EC) No 1333/2008 on food additives — European Union. https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32008R1333 ↩ ↩² ↩³ ↩⁴

2. Aluminum sulfate (compound summary: identity and formula) — PubChem, National Institutes of Health. https://pubchem.ncbi.nlm.nih.gov/compound/24850 ↩ ↩²

3. Commission Regulation (EU) No 231/2012 (food additive specifications) — European Union. https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32012R0231 ↩ ↩² ↩³

4. Safety of aluminium from dietary intake (TWI 1 mg/kg bw/week) — European Food Safety Authority (EFSA Journal). https://www.efsa.europa.eu/en/efsajournal/pub/754 ↩ ↩² ↩³

5. Toxicological Profile for Aluminum — Agency for Toxic Substances and Disease Registry (ATSDR), U.S. CDC. https://www.atsdr.cdc.gov/toxprofiles/tp22.pdf ↩