Tofu, or bean curd, has been an everyday food in Asia for over 2,000 years. Legend says it was discovered by Prince Liu An when he accidentally added impure sea salt (containing calcium and magnesium salts) to a pot of soy milk, causing it to curdle. This is the same basic chemistry used to make cheese from dairy milk. The soy milk proteins (globulins) denature and coagulate into a solid mass. Tofu is a complete protein, meaning it contains all nine essential amino acids. In the West, tofu became popular in the 1970s as a meat substitute. Because it is porous and neutral in flavor, it acts as a 'culinary sponge,' absorbing the flavors of whatever it is cooked with.