by Arnold Kuntz Ph. D. (Author) Miso is a Japanese word that means "fermented beans." Miso is usually found in the form of a thick paste, and the beans used during fermentation are almost always soybeans. During the soybean fermentation process, grains like barley, rice, or buckwheat might be added to achieve a certain flavor or other desired attribute, but in most situations, soybeans serve as the basis for miso fermentation. (This basic role of soybeans in preparation of miso can sometimes be overlooked because many varieties of miso may take on the name of their added ingredients, like "barley miso" or "rice miso." Yet virtually all of these miso varieties will contain soybeans as a basic ingredient.)It's worth noting that under some circumstances, you might hear the word "miso" being used to refer to fermentation of a food other than soybeans. A good example is "fish miso." In this case, the term "miso" is being used to refer to the process of fermentation rather than the food being fermented. "Fish miso" is a term used to describe fish that has been fermented using the same basic fermentation process that can be used to produce soy miso, barley miso, or rice miso.This use of the word "miso" in relationship to fish is important, because it tells us something very special about the miso fermentation process. For many miso eaters, the magic of miso lies in the micro-organism used for its fermentation: Aspergillus oryzae. This micro-organism is a particular type of fungus (a filamentous fungus, also called a "mold") that plays a special role in Japanese and other Asian cuisines. Long before scientists had developed ways of identifying and naming fungi like Aspergillus, cultures in China and Japan had developed special methods of fermenting soybeans (and other foods) that were practical and could be reproduced (assuring that the same mold was used, even though this mold was not yet scientifically identified). "Koji" was the term used to describe the end result when foods were fermented in this special way.When scientists eventually discovered that the Aspergillus fungus was the key micro-organism involved with koji fermentation, the word "koji" took on a second meaning. While remaining the name for the end-stage product, it also became the name for the Aspergillus fungus itself. Therefore, you can now hear the word "koji" being used to refer to end-products of Aspergillus fermentation like miso or sake or soy sauce, as well as to the Aspergillus mold itself.