E536 - Potassium ferrocyanide

At a glance

• What it is: A stable potassium salt of the hexacyanoferrate(II) complex, usually as a trihydrate.
• Also called: E536, Yellow prussiate of potash.
• What it does: Keeps salt free-flowing by preventing clumps.
• Where it’s found: Table salt, iodized salt, sea salt, and some salt substitutes.
• Typical level: Very small—often up to 20 mg per kg of salt, depending on local rules.
• Appearance: Pale yellow crystals; dissolves in water.

Why is Potassium ferrocyanide added to food?

Manufacturers add E536 to stop salt from clumping when it meets moisture in the air. Free‑flowing salt mixes and measures more evenly, which helps both home cooks and food producers. Scientific reviews have confirmed its technological function and very low toxicity at permitted levels.¹

What foods contain Potassium ferrocyanide?

• Table salt (regular, sea, and iodized)
• Low‑sodium salt blends and salt substitutes, often based on potassium chloride
• Seasoning mixes and spice blends that use treated salt

Internationally, the Codex General Standard for Food Additives (GSFA) permits potassium ferrocyanide in salt up to 20 mg/kg, which illustrates the small amounts used.²

What can replace Potassium ferrocyanide?

If you want salt without E536, you can:

• Choose salts labeled “no anti‑caking agents”
• Use a grinder or coarser salt crystals
• Store salt airtight to reduce moisture

Other anti‑caking agents sometimes used in salt include:

• Silicon dioxide
• Calcium silicate
• Magnesium carbonates
• Tricalcium phosphate
• Calcium ferrocyanide

How is Potassium ferrocyanide made?

Potassium ferrocyanide is the potassium salt of the hexacyanoferrate(II) complex and is typically sold as the trihydrate, with the formula K4[Fe(CN)6]·3H2O.³ Food‑grade E536 must meet strict identity and purity specifications set in law, including limits for impurities and heavy metals.⁴

Is Potassium ferrocyanide safe to eat?

Yes—when used as approved. The European Food Safety Authority (EFSA) set a group acceptable daily intake (ADI) for ferrocyanides of 0.03 mg per kg of body weight per day (expressed as cyanide) and concluded current uses in foods like salt are safe.¹ The small permitted use level in salt (for example, up to 20 mg/kg under Codex) further limits exposure.² While strong acids can break down ferrocyanide complexes to release hydrogen cyanide, this does not occur under normal food use; the compound is stable in typical food and body conditions.³

Does Potassium ferrocyanide have any benefits?

• Makes salt pourable and easy to measure
• Helps seasonings mix evenly
• Reduces clogged shakers in humid environments

These are technological benefits; it does not provide nutritional value.

Who should avoid Potassium ferrocyanide?

• People who prefer additive‑free salt can choose products labeled without anti‑caking agents.
• If your healthcare provider advises avoiding specific additives, check salt labels and pick simple alternatives.

Note: If you use salt substitutes based on potassium chloride, follow medical advice about potassium intake; that guidance relates to the salt substitute itself, not E536.

Myths & facts

• Myth: “It adds cyanide to my salt.” Fact: The cyanide is tightly bound to iron in a stable complex and is not released under normal food conditions.³
• Myth: “It isn’t allowed by international food standards.” Fact: Codex—the international food standards body—permits potassium ferrocyanide in salt at very low levels.²
• Myth: “It’s the same as toxic cyanide salts.” Fact: Potassium ferrocyanide is a different chemical with different properties and low toxicity at approved uses.³

Potassium ferrocyanide in branded foods

On retail packages, you’ll usually see it listed as “potassium ferrocyanide,” “yellow prussiate of potash,” or “E536” on table salt and some salt substitutes. Seasoning mixes that use treated salt may also list it, depending on local labeling rules. If you want to avoid it, choose salts marked “no anti‑caking agents.”

References

Footnotes

1. Re‑evaluation of ferrocyanides (E 535–538) as food additives — European Food Safety Authority (EFSA). https://www.efsa.europa.eu/en/efsajournal/pub/5364 ↩ ↩²

2. Potassium ferrocyanide (INS 536) — Codex GSFA Online. https://www.fao.org/gsfaonline/additives/details.html?id=81 ↩ ↩² ↩³

3. Potassium hexacyanoferrate(II) — PubChem (NIH). https://pubchem.ncbi.nlm.nih.gov/compound/26268 ↩ ↩² ↩³ ↩⁴

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