Any food additive with “cyanide” in the name makes me pause. Cyanide is one of the deadliest poisons known to man. Cyanide releasing compounds are found in some of the foods we eat and these foods must be thoroughly cooked or processed to render them safe. So, why in the world add such a compound to food? Potassium ferrocyanide (E 536) is an anti-caking additive that is used to keep granulated salt from clumping together in the container. It is also called yellow prussiate of potash, and potassium hexacyanoferrate. Consumers are afraid that this compound may release free cyanide when used in cooking. There are also reports that it is capable of releasing a toxic gas when combined with acids. How safe is this food additive?
Why Is Potassium Ferrocyanide Used in Salt?
Potassium ferrocyanide is added to salt as an anti-caking agent. Anti-caking food agents are compounds that can absorb moisture to help keep dry granulated or powedered food products from forming clumps. Without the use of anticaking additives, salt (NaCl) will attract moisture and form clumps that keep it from being free-flowing.
Is Potassium Ferrocyanide Safe?
Potassium ferrocyanide is the potassium salt of iron and cyanide. While very high levels of this compound are toxic and can cause kidney damage, the amounts of this anti-caking agent used in salt is quite small. In humans, the oral toxicity of potassium ferrocyanide is 5000 mg/kg. In other words, a 70 kg (154 lbs.) person would have to ingest 350 grams, or 0.9 lbs of the chemical to reach acutely toxic levels. The amount added to table salt for anticaking purposes is around 20 mg per kilogram of salt. This amount is so small that you would have to eat enough around 45,000 pounds (20412 kg) of salt to equal the toxic amount of potassium ferrocyanide for a 154 lbs. (70 kg) person.
The cyanide in potassium ferrocyanide is tightly bound to the iron so the compound goes through the digestive system unchanged. Normal cooking conditions will not rupture these chemical bonds. While highly acidic conditions could potentially cause the release of cyanide gas, this requires exceedingly strong acids not used in cooking. The gastric acid in your stomach is much too weak to cause this to occur.
When used in appropriate amounts, potassium ferrocyanide is considered to be a safe food additive according to the European Food Safety Authority, the U.S. Food and Drug Administration (FDA), and the World Health Organization (WHO). There is no danger of free cyanide release and the amount used in salt is many times smaller than the amount of cyanide compounds you are exposed to in everyday foods, including nuts and seeds. According to all the available and current data on this food additive, when used appropriately, it has no impact on human health. 1,2
- EFSA ANS Panel (EFSA Panel on Food Additives and Nutrient Sources added to Food), Younes M, Aggett P, Aguilar F, Crebelli R, Dusemund B, Filipič M, Frutos MJ, Galtier P, Gott D, Gundert-Remy U, Kuhnle GG, Lambré C, Leblanc J-C, Lillegaard IT, Moldeus P, Mortensen A, Oskarsson A, Stankovic I, Waalkens-Berendsen I, Wright M, Di Domenico A, Van Loveren H, Giarola A, Horvath Z, Lodi F and Woutersen RA, 2018. Scientific Opinion on the re-evaluation of sodium ferrocyanide (E 535), potassium ferrocyanide (E 536) and calcium ferrocyanide (E 538) as food additives. EFSA Journal 2018;16(7):5374, 26 pp. https://doi.org/10.2903/j.efsa.2018.5374
- Safety Data Sheet: Potatassium Ferrocyanide. Global Safety Management. https://www.uprm.edu/citai/wp-content/uploads/sites/222/2021/06/Potassium-ferricyanide.pdf