How tofu is made
Turning soybeans into tofu requires soaking, crushing, cooking, and filtering to create a soy milk. Coagulants are added to the milk to solidify it, then the tofu is molded into blocks and packaged in water or vacuum-packed without (for a longer shelf life) and refrigerated.
These traditional forms of tofu may be fairly coarse and firm to quite soft, depending on how much whey was pressed out.
In a newer method, the soy milk is poured into an aseptic package. Coagulants are added, and the package is sealed and heated. The resulting tofu is smooth and custardlike ― what manufacturers call silken.
There are no industry standards for describing the firmness of tofu; labels vary widely among brands. In general, however, use soft tofu, such as aseptic-packed silken styles, when you want a smooth, creamy texture but don't need the substance to hold its shape.
Choose firm, medium-dense tofu for all-purpose uses, such as in purées or cut into chunks (perfect tidbits for toddlers). Use extra-firm tofu (sometimes labeled nigari), which holds its shape well, in sautés and stir-fries and on the grill.