I have found this only very occasionally in Tofu. (Maybe about 3 or 4 times, ever: that would be something betw. 5-10%?, I imagine) I don't think the Tofu is spoiled since the date is fine, and it ...
Many recipes for tofu start from soymilk, many others start from scratch, but most of either kind share a whole variety of approaches, i.e. the order of the soaking, boiling and blending operations, ...