If you have purchased UHT soy milk then we are very sorry but it won’t work! This is because the proteins in the soy milk denature and are damaged which prevent forming a good curd-like structure.
As the instructions state it must be fresh, pasteurised soy milk. The better the soy milk, the better the tofu. We highly recommend making your own soy milk as this will ensure you get the freshest, most firm and delicious tofu. It does take a little time but most of that is letting the soybeans soak in water overnight, absolutely worth the effort and you will definitely taste the difference. See the How to Guide for Tofu for how to make it.
Soybeans are significantly cheaper to buy than soy milk too!
The main problem that we have had with store-bought soy milk is that it is a bit of an unknown – any added ingredients such as oils, sweeteners or preservatives, gums and thickeners which interfere with getting a good final structure and will therefore have a big impact on your tofu and likely cause it to fail.
If you don’t have time to make your own soy milk (it’s really easy we promise!) then your nearest Asian grocer is the best place to get fresh, pasteurised soy milk. You can usually get 100% soy milk which contain no gums etc from there. Make sure you purchase fresh soy milk, not UHT, heat-treated or one containing any additional ingredients. Only fresh soy milk will work to make tofu.