Potassium Ferrocyanide
The short version
The standard EU anti-caking agent for table salt — controversial in popular health narratives, regulated at very low residual.
It's permitted and generally considered safe, but there are a few reasons to be mindful — like sensitivities in some people, debated studies, or intake limits. The Safety section below explains the specifics.
Where it comes from
Manufactured by reaction of hydrogen cyanide with iron salts in the presence of potassium hydroxide. The historic name 'yellow prussiate of potash' refers to the Prussian-blue family of iron-cyanide complexes.
How it's used
The dominant anti-caking agent in EU table salt (typical residual 5–20 mg/kg, with regulatory maximum 14 mg/kg as anhydrous salt). Also used in wine clarification ('blue fining') to remove copper and iron, and in some rock-salt processing.
Safety profile
ADI of 0–0.025 mg/kg body weight (JECFA). Despite the cyanide groups in the formula, the iron-cyanide complex is thermodynamically very stable and the cyanide is not released under physiological conditions. Repeated misinformation panics around table salt do not reflect the actual chemistry. Banned in some countries (e.g., a few US states' organic standards) more on precautionary than evidence-based grounds.
Physical & chemical properties
Yellow crystalline powder, soluble in water. The yellow color comes from the iron-cyanide chromophore. Stable in dry storage.
Regulation worldwide
Permitted in the EU and most jurisdictions for salt with strict maximum residual limits. Not approved as a direct food additive in the US (where US table salt uses sodium ferrocyanide or alternative agents).
Educational information only. Not medical or dietary advice.