This homemade tofu thing is getting complicated.
Yesterday, I came across this information from Wholesome Living, an organic shop in Singapore that conducts all sorts of cooking workshops:
Commercial bean curds contain chemical substances such as bleaching agent, de-foaming agent, preservatives and coagulant (calcium sulfate a.k.a. gypsum). Commercial tofu manufacturers usually utilize calcium sulfate as a coagulant and marketing it as high calcium food to mislead consumers that it is a good source of calcium to prevent osteoporosis. In fact, this inorganic calcium will cause various health problems such as renal stone problems and so forth. Furthermore from the TCM (Traditional Chinese Medicine) perspective, consuming too much commercial tofu will make your body too ‘YING’.
Various websites, especially those promoting particular brands of calcium supplements based on water-soluble organic calcium (e.g. calcium aspartate etc.), support these points; see here, here and here.
On the TCM view of tofu, Paul Pitchford’s fantastic book, Healing with Wholefoods, elaborates:
For most people, its yin, cooling quality needs to be altered by thorough cooking; adding warming spices such as ginger is particularly helpful for cold persons. . . . Eating massive amounts of tofu regularly (as some Americans do) can contribute to kidney-adrenal weakness, loss and graying of hair, impotence, frigidity and decrease in sexual sensitivity.
At the same time, calcium sulphate is the oldest tofu coagulant used in China, with 2000 years of history (see here).
According to this Singapore-oriented discussion thread from 2005, Phoon Huat stopped selling gypsum (sometimes mistakenly equated with borax) as it was banned from sale, and therefore began stocking Glucono delta-lactone/GDL instead.
(GDL), which is naturally found in honey, fruit juices and wine, is the coagulant used for making silken tofu. As the Wholesome Living workshop teaches the making of silken tofu, I suspect GDL is the ‘non-mineral coagulant’ being used. The action of GDL is different from nigari & gypsum type coagulants as it works as an acid, not as a salt (see Asian Foods: Science and Technology by Catharina Yung-Kang, Wang Ang, KeShun Liu, Yao-Wen Huang).
Sounds like GDL is the way to go, especially for soft tofu for 豆花 douhua/tau foo fa/tau huay.