From The Food Encyclopedia by Jacques Rolland and Carol Sherman
A fermented soybean paste whose Chinese origins can be traced back to the 3rd century BC. It was known as hisio and wasn't imported to Japan until the 6th century, when it became a necessary part of the samurai diet. To make miso, soybeans are boiled and cooled, then grain is added, usually rice, barley or wheat, to initiate fermentation, which can last from weeks to years. Miso soup was not seen in Japan until the 20th century; the Chinese never used miso in soup.
