I made some fresh tofu fa following this recipe: http://ieatishootipost.sg/how-to-make-tau-huay-tofu-fa-almost-everything-you-need-to-know/
When I eat the tofu (about half an hour after pouring, so it just set), the tofu is sour, especially at the bottom.
I followed the recipe, but used gypsum instead (2 tsp).
The soybeans were soaked overnight, then shelled, and thinking it might have been my water, I used bottled spring water.
I've read that lactone can make the tofu sour, but I used food grade gypsum.