Whey is a by-product of cheese and tofu making.
In cheese-making, Whey is the liquid left over after the fat and protein in the cheese have coagulated to make curds. The whey will, however, still contain some protein that other cheeses can be made from. Cheeses made from whey include Ricotta Cheese, Cottage Cheese and Norwegian Goat Cheese (Gjetost.) Whey can also be used as a coagulant for the next batch of cheese, as it sometimes is in making paneer.
Whey is also a by-product of making tofu. Soy milk is coagulated into curds and whey. The curds are used to make tofu. The whey is drained off; the more whey that is drained off, the firmer the tofu will be. The whey can be yellow or amber in colour.
Tofu whey can be used as livestock feed, or it can be used to coagulate the next batch of tofu. To make leftover tofu whey into a coagulant, save about 3 pints or 7 to 8 cups of the whey. Leave for two weeks at room temperature in a sealed container. After that, store in refrigerator. To use, use about 1/2 to 2/3 of it, depending on how much you need, and replace what you use from the fresh batch of whey. The amount of whey coagulant you use will be about 20 to 25% as much of the soymilk you are using. Pour slowly in, seeing how it does and how much you actually need.