Soy sauce is a brown, salty fermented liquid used as a condiment in many southeast Asian cuisines. Soy sauce has been made for thousands of years, beginning in China nearly 5,000 years ago. Soy sauce probably began as a byproduct of preserving foods in salt -- these liquids were known as jiang. Jiang could be made from meat, fish or different grains, and over time, the jiang made from soybeans and wheat became popular, as they were easier to produce than meat-based jiang.
In the 7th century, Buddhist monks introduced soy sauce into Japan, where wheat-based versions became popular. These are known as shoyu, and are lighter, sweeter and less salty than Chinese versions of soy sauce, with a sherry-like oxidative note.
Traditional methods of soy sauce production rely on boiled soybeans and roasted wheat, are added to water and salt, and are fermented by koji, a term used for a blend of molds in the Aspergillus family (which also are used to produce sake). Over time, the koji converts starch to sugar and a wild fermentation takes over, producing not only low amounts of alcohol, but also lactic acid. After a few months, the liquid is heated, filtered and bottled.
Industrial soy sauce is made mainly from hydrolyzed soy protein, and typically manufactured in three days. Inexpensive soy sauce is typically made using this method.
All soy sauce is high in umami, a fifth taste first identified in 1908 by Kikunae Ikeda. Umami is a meaty-savory flavor that is the result of naturally occurring glutamates in soy sauce.
In some food cultures, soy sauce is used to produce other condiments, such as ponzu shoyu, a Japanese mixture of mirin, soy, citrus juice and konbu. In Indonesia, soy sauce is used as the base for kecap manis, which is sweetened with palm sugar.