I bought gypsum for my ale making venture and googled it to see what culianry uses it may have other than making water hard for brewing purposes. It's also a coagulant that can be used for tofu (nigari is more common/traditional). Using Just Hungry's recipes for soy milk and then for tofu, I had even more success than I had expected. It came out very firm, much like the Japanese tofu that I'd get at the Rainbow Co-op bulk section when I lived in SF. (Lately I've been getting the "AFC" pressed bean curd at local Asian markets -- It's halfway between that and supermarket "firm" tofu).
It starts off with boiling puréed, soaked soy beans:
After twenty minutes, it gets strained and is soymilk!
That is heated back up to 175ºF, and the coagulant (gypsum or magnesium cloride [nigari]) is added. It sits for fifteen minutes. I then added a bit more gypsum for good measure. And it is strained:
It gets shaped (in that towel, just in a colander in this case), and voilà: