E505 - Ferrous carbonate

At a glance

• What it is: An iron(II) salt of carbonic acid; chemical formula FeCO3.
• What it does: A less common additive used where an iron source or iron-based processing function is desired.
• Where you’ll see it: Ingredient lists may show “ferrous carbonate” or “E505”; many makers instead use related iron salts such as iron gluconate or ferrous lactate.
• Safety: Authorized in the EU with strict purity criteria; as a source of iron, too much overall iron from diet and supplements can be harmful for some people.

Why is ferrous carbonate added to food?

Producers may use ferrous carbonate when they need an iron-based additive, for example to support processing aims or to contribute iron. In the European Union, ferrous carbonate is an authorized food additive with identity and purity criteria set in law.¹ In practice, many foods that need an iron salt for color stabilization use other forms such as ferrous gluconate or ferrous lactate instead.²

What foods contain ferrous carbonate?

You are most likely to encounter ferrous carbonate in niche or regional products rather than in everyday staples. If it is used, it will appear in the ingredients as “ferrous carbonate” or “E505.” Related iron salts are more commonly found on labels, particularly in canned ripe olives, which typically use iron gluconate or ferrous lactate.²

What can replace ferrous carbonate?

• Other iron salts: Food makers often choose iron gluconate or ferrous lactate when an iron-based additive is needed, especially for stabilizing the black color of ripe olives.²
• Non-iron options: Depending on the job (for example, texture or color stability), different additives or process changes may be used instead. The best substitute depends on the food and the desired effect.

How is ferrous carbonate made?

Ferrous carbonate is the iron(II) salt of carbonic acid with the formula FeCO3.³ Commercial production methods can vary, but the finished additive must meet the European Union’s identity and purity specifications before it can be used in foods.¹

Is ferrous carbonate safe to eat?

When used as permitted and meeting legal purity criteria, ferrous carbonate is considered acceptable for use in the EU food supply.¹ Like other iron sources, excessive intake of iron from foods and supplements can cause stomach upset and, at very high levels, more serious effects; the U.S. National Institutes of Health lists a Tolerable Upper Intake Level (UL) of 45 mg/day for adults from all sources.⁴

Does ferrous carbonate have any benefits?

As an iron compound, it can contribute small amounts of dietary iron. Iron supports normal oxygen transport in the blood and helps reduce tiredness when a person is iron-deficient.⁴ That said, food makers often choose other iron salts when fortification is the primary goal, so the practical benefit depends on the product and how much is used.

Who should avoid ferrous carbonate?

• People with iron overload disorders: Individuals with hereditary hemochromatosis or other iron-loading conditions should avoid extra iron unless advised by their clinician.⁵
• Those on iron-restricted medical diets: Follow healthcare guidance on total iron intake, including from fortified foods and additives.⁴

Myths & facts

• “All E‑numbers are artificial.” Myth. E‑numbers include both synthetic and mineral or plant-derived substances; ferrous carbonate is a mineral iron salt.
• “Ferrous carbonate is the same as metallic iron.” Myth. It is a compound of iron and carbonate (FeCO3), not elemental iron.³
• “If a product contains an iron additive, it must be unsafe.” Myth. Safety depends on the specific additive, its purity, and how much is used, which are controlled by food laws.¹

Ferrous carbonate in branded foods

Label wording varies by market. If used, you’ll see “ferrous carbonate” or “E505” on the ingredient list. Many large brands opt for different iron salts, so spotting E505 on mainstream labels is uncommon; always check the packaging of the specific product.

References

Footnotes

1. Commission Regulation (EU) No 231/2012 laying down specifications for food additives listed in Annexes II and III to Regulation (EC) No 1333/2008 — EUR-Lex. https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32012R0231 ↩ ↩² ↩³ ↩⁴

2. 21 CFR § 155.190 Canned ripe olives — U.S. Food and Drug Administration (Standard of Identity permitting ferrous gluconate or ferrous lactate). https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-155/section-155.190 ↩ ↩² ↩³

3. Ferrous carbonate — PubChem, National Institutes of Health. https://pubchem.ncbi.nlm.nih.gov/compound/FeCO3 ↩ ↩²

4. Iron Fact Sheet for Health Professionals — National Institutes of Health, Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/ ↩ ↩² ↩³

5. Hereditary Hemochromatosis — Centers for Disease Control and Prevention. https://www.cdc.gov/ncbddd/hemochromatosis/index.html ↩