More than some other ingredients, choosing the best bean curd can depend on its intended use. The two main types available, firm and silken, might not always be interchangeable, because the silken variety is very soft and cannot hold its shape in some instances. More exotic varieties of bean curd can be used for a different flavor or texture, such as puffed curd, fried curd or fermented curd. The type of coagulant used to create the curd can occasionally make some nutritional difference so the curd provides additional dietary benefits. The way the curd, or tofu, is packaged and sold also can be a determining factor when deciding which bean curd is the best.
Bean curd can be classified as silken or firm, and there are some smaller gradations within those two categories. Silken curd has a very soft texture and contains a large amount of moisture. It is more like a thick pudding than a solid block and can easily be whipped or incorporated into a sauce. In general, silken varieties are not usually added to fried dishes, because they can break down into small bits that can easily dry out or vanish completely.
Firm bean curd is made in the same way as the silken type, except it is pressed to remove some of the moisture. The firmer curd is able to be cut into pieces or slices and used in dishes like any other ingredient, because it will hold its shape well. The curd can be baked, fried, eaten raw or used in stews, where it will take on the character of the sauce it is in. Very firm varieties are available that are sometimes as solid as cheese and can withstand very rough handling without breaking apart.
Some recipes can be enhanced by using less common types of bean curd. A strong, sharp flavor can be added if fermented curd is used, because it is aged in vinegar and a variety of other ingredients. Fried curd can be used as a substitute for meats or vegetables, because it has a caramelized surface and a firm texture. As a readymade ingredient or as a garnish, curd that has been deep fried until it is puffed can be used for crunch.
During the process of making bean curd, a special ingredient known as a coagulant is added to soybean milk to form the curd. Some of these coagulants, specifically calcium sulfate, will leave excess calcium in the curd. This extra calcium can provide a small amount of extra nutritional value that other coagulants cannot.
The way in which the bean curd is packaged and sold also can make a difference. Many brands are in tightly sealed packages or are frozen and, generally, safe. In some instances, however, the curd is displayed floating in an open container full of water and customers remove blocks of curd as needed. These vats sometimes offer optimal conditions for bacteria to grow in the curd; as with other foods, however, the bacteria generally are killed if the curd is cooked thoroughly.