Tofu is a food made of condensed soy milk that is pressed into solid white blocks in a process quite similar to cheesemaking. It originated inChina. A Chinese cook discovered tofu more than 2,000 years ago by accidentally mixing a batch of fresh soy milk with nigari. Nigari is what remains when salt is extracted from seawater. It is a mineral-rich coagulant used to help tofu solidify and keep its form.