E521 - Aluminium sodium sulphate

At a glance

• E-number: E521; also labeled as sodium aluminium sulfate or soda alum
• Role: Acid in baking powders; helps baked goods rise
• Typical foods: Baking powder, self-rising flour, some dry mixes
• Related additives: other “alums” like E520, E522, E523; sometimes paired with sodium bicarbonate
• Diet notes: Mineral salt, vegan and gluten-free by nature
• Safety: Regulated; total aluminium intake has recommended limits in the EU

Why is aluminium sodium sulphate added to food?

This additive is an acid that works with baking soda to create carbon dioxide gas. The bubbles make cakes, muffins, and biscuits rise. It is often part of “double-acting” baking powders: some gas is released when the batter is mixed, and more is released during baking for a steady lift.

Bakers and manufacturers choose E521 because it is stable in dry mixes and gives a reliable rise in the oven. It can also be blended with other acids to fine-tune the leavening profile.

What foods contain aluminium sodium sulphate?

You are most likely to see E521 in:

• Baking powder
• Self-rising flour
• Pancake, waffle, biscuit, and cake dry mixes

In the United States, the federal standard of identity for self-rising flour lists sodium aluminum sulfate as one of the allowed acid-reacting materials in the leavening system.¹

What can replace aluminium sodium sulphate?

Alternatives depend on the recipe and desired rise:

• Non-aluminium leavening acids such as monocalcium phosphate or disodium diphosphate (also called SAPP)
• Organic acids in home baking, like citric acid
• Slow-acting options such as glucono delta-lactone
• If aluminium is acceptable but a different profile is needed, some blends use sodium aluminium phosphate

Swapping one acid for another can change flavor and timing, so formulas often need adjustment.

How is aluminium sodium sulphate made?

Aluminium sodium sulphate is a “double salt” of aluminium sulfate and sodium sulfate, commonly crystallized as a dodecahydrate. In other words, it forms stable crystals that include water molecules, which helps keep it free-flowing and easy to blend into dry mixes.²

Is aluminium sodium sulphate safe to eat?

In the U.S., the Food and Drug Administration (FDA) includes sodium aluminum sulfate on its Food Additive Status List as permitted when used in line with good manufacturing practice.³ In the European Union, the European Food Safety Authority (EFSA) set a tolerable weekly intake (TWI) for total aluminium from all dietary sources at 1 mg per kilogram of body weight per week.⁴ That TWI applies to aluminium from all food sources, not just E521, and helps authorities set and review use limits.⁴

Only a small amount of ingested aluminium is absorbed, and healthy kidneys remove most of it. People with reduced kidney function can retain more aluminium, which is why medical guidance may limit exposure in those cases.⁵

Does aluminium sodium sulphate have any benefits?

• Provides steady, “double-acting” leavening for even rise
• Stable in dry blends like baking powder and self-rising flour
• Helps manage flavor and texture by controlling when gas is released in batter or dough

These features make it useful in shelf-stable mixes that must perform consistently.

Who should avoid aluminium sodium sulphate?

• People with chronic kidney disease or those on aluminium-restricted medical diets should seek advice from their healthcare provider, since their bodies may clear aluminium less efficiently.⁵
• Anyone advised to limit total aluminium intake should check all sources of aluminium in their diet, not only food additives.⁴

Myths & facts

• Myth: All aluminium in food causes Alzheimer’s disease. Fact: Health agencies note that evidence does not show a clear cause-and-effect link between typical dietary aluminium exposure and Alzheimer’s disease; regulators continue to manage aluminium additives with safety limits.⁵⁴
• Myth: Any aluminium-based leavening makes baked goods taste metallic. Fact: In properly formulated recipes, off-flavors are not expected; problems usually come from imbalanced leavening or too much acid.

Aluminium sodium sulphate in branded foods

Ingredient lists are the best guide. Look for “sodium aluminium sulfate,” “aluminium sodium sulphate,” or “E521” on baking powder, self-rising flour, and dry baking mixes. Similar names you might see on labels include other “alums,” such as aluminium sulphate, aluminium potassium sulphate, and aluminium ammonium sulphate; these are related but not identical.

References

Footnotes

1. Self-rising flour; identity — 21 CFR 137.180, eCFR (U.S. National Archives). https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-137/section-137.180 ↩

2. Sodium aluminum sulfate (substance record) — PubChem, NIH. https://pubchem.ncbi.nlm.nih.gov/compound/Sodium-aluminum-sulfate ↩

3. Food Additive Status List — U.S. FDA. https://www.fda.gov/food/food-additives-petitions/food-additive-status-list ↩

4. Safety of aluminium from dietary intake (re-evaluation of aluminium-containing food additives) — EFSA Journal. https://www.efsa.europa.eu/en/efsajournal/pub/754 ↩ ↩² ↩³ ↩⁴

5. Toxicological Profile for Aluminum — ATSDR/CDC. https://www.atsdr.cdc.gov/toxprofiles/tp22.pdf ↩ ↩² ↩³