Aluminium Potassium Sulfate
The short version
Potash alum — the classical pickle-firmer and double-acting-baking-powder acid, now restricted in EU.
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
Crystallized from solutions of aluminium sulfate and potassium sulfate. The dodecahydrate forms large clear octahedral crystals — the geological mineral kalinite. One of the oldest deliberately purified chemicals (Roman and medieval use as a mordant and styptic).
How it's used
Firming agent for pickles and brined vegetables (the crisp, sharp 'pickle alum' historically), a slow leavening acid in double-acting baking powders, and an egg-white whipping aid. Largely replaced by calcium chloride and cream of tartar in EU consumer products following the 2008 aluminium re-evaluation.
Safety profile
ADI of 0–1 mg/kg body weight (combined aluminium). Soluble aluminium forms (like alum) contribute more to absorbed aluminium than metallic or insoluble forms — same EFSA concern that lowered the ADI.
Physical & chemical properties
Colorless crystalline solid (large octahedral crystals as the dodecahydrate). Soluble in water with mildly acidic solution. Astringent taste.
Regulation worldwide
Permitted in the US with specific use categories. Largely de-listed for general EU food use; narrow applications retained.
Educational information only. Not medical or dietary advice.