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I'm doing a chemistry project on ionic compounds found on food labels, and I can't find a clear article on how calcium sulfate is made for edible foods. I know it comes from calcium sulfate dihydrate. I have found articles on how they turn that into calcium sulfate for fertilizer, concrete, drywall, and other materials, but not for food products.

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Use of calcium sulfate in food and pharmaceutical applications is widespread and continues to expand. United States Gypsum Company offers two highly refined calcium sulfate products: USG Terra Alba and SNOW WHITE filler. Both fillers are food- and pharmaceutical-grade forms of calcium sulfate, a mineral that appears on the Food and Drug Administration’s GRAS (Generally Recognized as Safe) list of additives approved for nutritional and functional use in food products.

  • USG Terra Alba ($\ce{CaSO4 \cdot 2H2O}$), the dihydrate form of calcium sulfate, results from fine-grinding and air-separating a select, high-purity white gypsum that contains about $20$ percent water of crystallization.
  • SNOW WHITE filler ($\ce{CaSO4}$), the anhydrous form of calcium sulfate, is produced by calcining and milling high-purity white gypsum$^{[1]}$.

Gypsum is made suitable for commercial use by a process called calcination, which involves heating the mineral to remove approximately three-quarters of its water. Calcined gypsum can recrystallize into any shape with the simple addition of water.$^{[2]}$.

Presumably through repeated calcination, gypsum is made pure enough to meet FDA standards.


$^{[1]}$ USG, Calcium Sulfate Fillers
$^{[2]}$ Encyclopedia.com, USG Corporation

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