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Introduction
Potassium ferrocyanide (K₄[Fe(CN)₆]·3H₂O) is the potassium salt of the same ferrocyanide complex. It is used as an anticaking agent in table salt, similarly to the sodium salt, and also as a fining agent in wine. It is approved as a food additive (E536) in the EU. Compared to sodium ferrocyanide, the potassium salt is more soluble in water and leaves a slightly different cation profile, which may be preferred in low-sodium salt products.
Like the sodium salt, potassium ferrocyanide is non-toxic because the cyanide groups are tightly bound to iron. It is also used as a component in some salt products intended for dietary potassium supplementation.
CAS Number
13943-58-3 (trihydrate). Anhydrous: 13408-27-6.
Synonyms
Potassium hexacyanoferrate(II), Yellow prussiate of potash (YPP), Potassium ferrocyanide trihydrate, E536.
Topic Headings
*1. Advantages over sodium ferrocyanide in low-sodium salts (paragraph form)*
For consumers on low-sodium diets, potassium chloride (KCl) is often used as a partial substitute for sodium chloride in "low-sodium" or "lite" salts. However, KCl is more hygroscopic than NaCl and tends to cake more easily. Potassium ferrocyanide is an effective anticaking agent for potassium chloride-based salts, with the same mechanism of crystal growth inhibition. Because the additive itself contains potassium rather than sodium, it does not reintroduce sodium into the product. In some formulations, a mixture of sodium ferrocyanide and potassium ferrocyanide is used to balance cation content. Additionally, potassium ferrocyanide is used in wine fining because the potassium ion forms less soluble precipitates with certain organic acids (e.g., potassium bitartrate) which is beneficial in cold stabilization of wine. The solubility of potassium ferrocyanide in water is about 29 g/100 mL at 20°C (compared to 17.5 g/100 mL for sodium salt), allowing for more concentrated solutions.
2. Physical and chemical properties (list form)
• Appearance — Lemon-yellow to yellow crystalline powder or granules.
• Odor — Odorless.
• Molecular weight — 422.39 g/mol (trihydrate); 368.35 g/mol (anhydrous).
• Melting point — Decomposes above 400°C.
• Solubility in water — 29 g/100 mL at 20°C; 77 g/100 mL at 100°C (highly soluble).
• Solubility in other solvents — Insoluble in ethanol.
• Stability — Very stable; decomposes in strong acids with release of HCN.
• pH (1% solution) — Approximately 9-10.
• Density — 1.85 g/cm³ (anhydrous).
3. Food applications and typical usage levels (list form)
• Anticaking agent in table salt (including low-sodium salt and potassium chloride) — 10-30 mg/kg; maximum 20-25 mg/kg as ferrocyanide.
• Wine fining (removal of copper, iron, and other metals) — 0.1-0.5 g/L; forms precipitates that are removed by filtration.
• Citric acid purification — To remove heavy metals.
• Food-grade salt for cheese and butter making — Prevents caking in high-humidity environments.
• Potassium fortification in salt substitutes — Provides additional potassium in some formulations.
4. Regulatory status and safety (paragraph form)
Potassium ferrocyanide is approved as E536 in the EU and as GRAS in the USA (21 CFR 184.1296, similar to sodium ferrocyanide). The same JECFA ADI applies: 0-0.025 mg/kg bw as ferrocyanide ion. The safety profile is identical to that of sodium ferrocyanide; the complex is non-toxic and does not release free cyanide. In wine fining, the ferrocyanide is precipitated and removed by filtration; residual levels are extremely low (typically below detection limit). For table salt, typical intake of ferrocyanide is less than 0.02 mg per day for a person consuming 10 g of salt daily, which is far below the ADI. The potassium form is sometimes preferred by manufacturers for organoleptic reasons (less aftertaste) and for marketing low-sodium products. There is no scientific evidence of any health risk from potassium ferrocyanide at authorized levels.
