Our favored coagulant to use for making tofu is nigari, the residue left when the sodium is extracted from seawater and evaporated (it contains magnesium chloride, magnesium sulfate, and other trace elements). Nigari is readily available from online retailers in liquid and crystal form. Molds specifically designed for making tofu can also be found online. To improvise a mold, have ready two 1-quart capacity food-safe plastic containers of the type that nest. Perforate the bottom and lower portion of one container with holes about ¼ inch in diameter as though on a 1-inch grid. The other container may be partly filled with water to act as a weight (half full, it will weigh 1 pound).
Prepare:
When the milk has finished simmering, remove from the heat and let cool for 5 minutes. To make a coagulant, mix together in a small bowl until dissolved:
(If using gypsum, you will need to restir the mixture right before each addition to the soy milk.) Gently stir one-third of the coagulant solution into the hot soy milk. Sprinkle another one-third of the coagulant over the surface of the milk, cover the pot, and let it sit for 3 minutes. Sprinkle the remaining solution over the milk and gently stir the surface. Cover for 3 minutes if using nigari, or 6 minutes if using Epsom salts or gypsum. If curds do not form during this period, mix together in a small bowl:
Stir this into the soy milk and let sit for an additional 5 minutes. Line the tofu mold (the container with the holes) with a generous square of moist, thin muslin cloth and place the container in the sink. Gradually ladle the soy curd mixture into the mold and fold the ends of the cloth over the top. Place the top of the mold over the curd and place a 1-pound weight over it for medium-firm tofu, or a 3-pound weight for firm tofu. Let the curds compress for 20 minutes or until the whey is no longer expressed. Very gently unwrap the curd. Tofu is highly perishable; store it refrigerated in water for only a few days.
To cook tofu, see About Tofu, Tempeh, and Other Plant-Based Proteins.