How is food-grade calcium sulfate made? 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.
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