How much calcium (if any) exists in tofu that may not be made with calcium sulphate?
You might ask the producers what they use as a coagulant for their tofu. If they say gypsum, that is calcium sulfate. If they say nigari, that is magnesium chloride. These are the two coagulants that are usually used; sometimes both are used together. How much calcium there is will also depend in part on the firmness of the finished tofu. For a general guideline, the USDA Nutrient Database online (http://www.nal.usda.gov/fnic/foodcomp/search) says that 100 g of firm tofu prepared with calcium sulfate has 683 mg of calcium and 100 g of extra firm tofu made with nigari contains 175 mg of calcium (I could not find “firm” tofu made with nigari in the database, but presumably it is lower in calcium than extra firm tofu is). This information provided by: Cheryl Sullivan, M.A., R.D.