Alum

Double salts of aluminium sulphate with the sulphate of a monovalent metal — the classic example being potash alum. Alums serve as coagulating agents in drinking-water purification, gathering suspended particles into settleable flocs. Food applications include use in colorants, the manufacture of cured jellyfish products, modification of starch properties, and processed fruit and vegetable products where they firm texture — the crispness of a pickled cucumber owes something to alum. A traditional, multi-purpose chemical bridging water treatment and the kitchen. Its long history shows how one mineral salt can serve industry and household alike.