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Firm tofu is a product made from soy milk that is curdled in a process similar to the way cheese is made. It is drier than silken tofu and is often used as a meat substitute because it can be prepared to have a meat-like consistency and has a high protein content. Firm tofu usually can be found at East Asian specialty food markets and in the dairy section of grocery stores that serve health-conscious and vegetarian or vegan customer bases.
Tofu is made from the curds that form when a coagulant is added to soy milk. Depending on the type of tofu being produced, these curds might then be wrapped in cloth and pressed to remove moisture. The amount of water removed determines into which of the three primary categories the resulting tofu will fall; soft tofu has the most moisture and is very smooth and slippery, and dry tofu has the least moisture and is dense and substantial. Firm tofu’s consistency is somewhere between the two, and it holds its shape through cooking while still being easy to cut and crumble.
Its versatile texture and ability to easily absorb flavors make firm tofu the most popular type of tofu for use in stir-fries, salads, stews and other dishes in which the ingredients are meant to maintain their shape. It is a common ingredient in East Asian cooking and can be marinated, baked, fried or grilled in the same fashion that meat is. Firm tofu has approximately the same protein content as an equivalent weight of hard-boiled eggs, so it is an excellent source of protein. For this reason, tofu is an integral part of many vegan and vegetarian diets, and there are numerous cookbooks with recipes in which it is the primary ingredient.
When purchased at a store, firm tofu generally will be sealed in a plastic package. It should be kept refrigerated and is best used shortly after it has been opened. If, however, not all of the tofu is used at once, the remainder can be stored in the refrigerator by placing it in a sealed container and covering it with water to keep it from drying out or absorbing other flavors. This water should be changed every one or two days, and the tofu should be used within a week. Tofu also can be frozen for as long as five months in either the original package or in a freezer-safe resealable plastic bag.
Tofu can be made at home by boiling either store-bought or homemade soy milk and adding a small amount of a coagulant such as magnesium chloride or calcium sulfate, then straining and pressing the curds. Any unpasteurized tofu — including homemade — should not be consumed raw, however, because there is a risk of unwanted bacteria. It should be boiled for five minutes or similarly cooked before being eaten.