The term “soy paste” is used to describe two different, but related materials. First, it is used to describe the slurry of fermented soy beans and other grains from which liquid soy sauce is pressed, as well as the cake of soy and other solids left over once all the soy sauce has been pressed out. Second, it can describe a preparation specifically developed for cooking — a thick paste consisting primarily of fermented soy beans, which is used as a base for stir-frying and in a variety of sauces added in cooking or as condiments.
The soy sauce available to modern consumers is the product of a process which involves the fermentation of soy beans. Different styles of soy sauce call for different combinations of raw ingredients, but ingredients common to most soy sauces are soybeans, salt, water and Aspergillus mold. Chinese soy sauce, considered to be the “original” soy sauce, is most commonly made only from soybeans, salt and Aspergillus. Some Chinese soy sauces include other grains, but in small quantities. Japanese soy sauce utilizes relatively equal parts of soybeans and a grain such as wheat, as well as the salt and mold.
Once the slurry has fermented and aged for as much as six months, the liquid is pressed out and further refined until it’s ready for sale. The first pressing of soy sauce is often bottled and sold separately; said to have a lighter flavor, it is usually reserved for dipping sauces. Some soy sauces are blended with other substances to produce differently flavored or textured sauces; when blended soy sauces are darker or thicker, such as dark mushroom soy sauce, it is usually used primarily for cooking. Once the soy sauce has been pressed out of the slurry, the leftover cake of soybean and grain is used either as fertilizer or animal feed.
Fermented soy paste is a traditional Korean flavoring. Consisting primarily of soybeans which are ground, boiled and fermented in a traditional process, it does not use the Aspergillus mold, but instead relies on naturally-occurring bacteria for fermentation. After about three months, solids and liquids are separated, with the liquid undergoing further processing to become Korean-style soy sauce, and the solid being bottled and sold as fermented soy paste or bean paste. Fermented soy paste has a consistency similar to that of peanut butter, and generally is not smooth, but will contain bits of fermented soy beans.
An excellent base for many dipping sauces and stir-frying liquids, fermented soy paste has a complex flavor which complements most non-sweet foods. It generally must be mixed with other liquids to facilitate its use as a sauce; two common such liquids are vinegar and chicken broth. Fermented soy paste can also be combined with sugar and other flavorings to make a delicious barbecue sauce.