What is E536?
Complete guide to understanding E536 (Potassium Ferrocyanide) — a safe anti-caking agent that contains cyanide but poses zero health risk
The Quick Answer
E536 (Potassium Ferrocyanide) is an anti-caking agent used in table salt to prevent clumping — and it’s completely safe despite containing cyanide.
What makes E536 unique and confusing: it contains cyanide atoms, which sounds dangerous, but the cyanide is permanently bonded to iron and cannot be released or absorbed. EFSA’s 2018 re-evaluation confirmed it poses zero safety concern. E536 is an example of how chemical composition doesn’t determine safety — the bonds and structure determine whether the compound can harm you.
E536 is safe, approved, and one of the best examples of how “scary-sounding” additives can actually be harmless.
📌 Quick Facts
- Chemical Name: Potassium Ferrocyanide; Yellow Prussiate of Potash
- Type: Anti-caking agent; food additive
- Chemical formula: K₄[Fe(CN)₆]·3H₂O
- Found in: Table salt; salt substitutes; some spices
- Contains: Cyanide (but irreversibly bonded; cannot be released)
- Safety Status: Approved and completely safe
- Approved by: EFSA, FDA, JECFA; most countries
- Permitted level: 20 mg/kg maximum in salt
- ADI (EFSA): 0.03 mg/kg body weight/day
- Main concern: NONE; safe at approved levels
What Exactly Is It?
E536 is potassium ferrocyanide, also called Yellow Prussiate of Potash — a yellow crystalline compound used to prevent salt from clumping — 100% synthetic, chemically engineered.
Chemical structure: Potassium (K₄) + Ferrocyanide complex [Fe(CN)₆] + Water (3H₂O)
Appearance: Lemon yellow crystals; very fine particles; odorless; bitter salty taste
Key properties:
– Anti-caking: prevents moisture absorption; keeps salt free-flowing
– Hygroscopic: absorbs water; prevents granule clumping
– Inert: stable; doesn’t react with salt or food
– Yellow color: from ferrocyanide complex and Fe2+ ions
– Heat stable: survives cooking without decomposition
– Water insoluble: doesn’t dissolve in water or stomach fluids
– Harmless: cyanide irreversibly bonded; cannot be released or absorbed
– Very fine particles: <10 micrometers diameter
Where You’ll Find E536
E536 is used almost exclusively in table salt as an anti-caking agent.
| Product | Use | Frequency |
|---|---|---|
| Table salt (refined) | Anti-caking agent; prevents clumping | Common (but not all brands) |
| Salt substitutes | Anti-caking agent | Some brands |
| Spice mixtures | Anti-caking (indirect through salt) | Rare |
| Animal feed salt | Anti-caking for livestock feed | Approved 2023 by EFSA |
| Other foods | None approved for direct use | N/A |
Rarity note: E536 is used but less common than sodium aluminosilicate (E554) or magnesium silicate (E553). Many salt manufacturers prefer alternatives or use no anti-caking agents.
Maximum permitted level (EU): 20 mg/kg (expressed as anhydrous potassium ferrocyanide)
To find E536: Check salt ingredient lists; look for “potassium ferrocyanide,” “E536,” “yellow prussiate of potash,” or similar names.
Is E536 Safe? Absolutely
EFSA 2018 Re-evaluation: Definitive Safety Assessment
The European Food Safety Authority completed comprehensive re-evaluation and concluded:
“Ferrocyanides (E 535–538) are of no safety concern at the current authorised use and use levels.”
Safety Assessment Details
| Criterion | Finding | Conclusion |
|---|---|---|
| Cyanide release in stomach | Iron-cyanide bonds stable at stomach pH and temperature; cannot be released | Safe |
| Cyanide release during cooking | Requires >400°C to decompose; cooking max ~200°C; bonds remain intact | Safe |
| Gastrointestinal absorption | Very low (0.25-0.42% in humans); mostly passes through unchanged | Safe |
| Bioaccumulation | No accumulation in tissues; excreted unchanged in feces | Safe |
| Acute toxicity | Very low at food use levels | Safe |
| Chronic toxicity | No adverse effects at permitted levels | Safe |
| Genotoxicity | No genetic damage concern | Safe |
| Carcinogenicity | No cancer risk identified | Safe |
| ADI (Acceptable Daily Intake) | 0.03 mg/kg body weight/day (expressed as ferrocyanide ion) | Safe at all realistic consumption levels |
Actual Consumption vs. Safety Limit
Real exposure calculation:
Maximum permitted level: 20 mg/kg in salt
Typical salt consumption: 5-10 g/day
E536 intake at max level: ~100-200 μg/day (0.0001-0.0002 mg/day)
EFSA ADI for 70 kg adult: 2.1 mg/day
Safety margin: 10,000x between actual consumption and ADI limit
To exceed ADI: Would require consuming ~15 teaspoons of salt daily at maximum permitted E536 level (extremely unrealistic)
Addressing the “Cyanide Concern”
Many people worry about E536 because it contains cyanide. This is understandable but misguided:
Misconception vs. Reality
| Misconception | Reality |
|---|---|
| “Contains cyanide, therefore toxic” | Cyanide is irreversibly bonded to iron; cannot be released or absorbed |
| “Stomach acid releases cyanide” | Iron-cyanide bonds stable at stomach pH; cyanide cannot be released |
| “Cooking releases cyanide” | Requires >400°C; cooking max ~200°C; bonds remain intact |
| “Accumulates in body” | Not absorbed significantly; passes through unchanged; excreted in feces |
| “Banned in UK/Europe” | Not banned; approved and used; EFSA confirmed safe 2018 |
| “Causes cancer/allergies” | EFSA found no genotoxicity or carcinogenicity concern |
Why Cyanide Is Irrelevant Here
Chemical composition doesn’t determine safety — the bonds and molecular structure do.
Example: Table salt contains chlorine (a toxic gas), but nobody worries about salt poisoning because chlorine is permanently bonded to sodium and cannot escape. Similarly, E536 contains cyanide, but it’s permanently bonded to iron and cannot escape.
EFSA’s key finding: “The Panel noted that at this ADI the potential amount of free cyanide released would not be of safety concern.”
In other words: Even EFSA calculated how much free cyanide might theoretically be released — and found it would be zero concern.
The Bottom Line
E536 (Potassium Ferrocyanide) is a completely safe anti-caking agent approved globally, despite containing cyanide atoms.
What you should know:
- It’s safe: EFSA definitively confirmed; zero safety concern
- It contains cyanide: But cyanide is permanently bonded; cannot be released
- It’s approved: EU, FDA, JECFA, most countries
- It’s commonly used: Found in many salt products
- You have huge safety margin: 10,000x between consumption and ADI limit
- It passes through unchanged: Not absorbed; excreted in feces
- No alternatives needed: E536 is genuinely safe; choosing different salt won’t reduce risk
