How Exactly Is Soy Sauce Made?

Soy sauce is made through a slow fermentation process that results from a chemical reaction created from combining four key raw ingredients — soybeans, salt, wheat, and water — with aspergillus, a type of mold, or a fermenting agent like koji mold. The soybeans are washed, soaked in water, and then steamed. The wheat is roasted, which activates its sweet taste, and then crushed to improve the fermentation process. A brine is created from salt and water, which reduces the risk of bacteria growth during fermentation as well as giving the soy sauce its signature salty taste. The mold is then mixed with the soybeans and wheat and left for three days, after which it is mixed with the salt water brine and put in a tank or other storage container. It is left to age for at least three months to allow the formation of lactic acid and the completion of the alcohol fermentation process, which is the real reason soy sauce contains alcohol.

After the fermentation process is complete, the resulting sauce is pressed between cloths to clarify it and make it smooth. This raw soy sauce is then aged another three days to allow the oil, sediment, and sauce to separate. The middle part, called clarified raw soy sauce, is removed and heated. This stops the fermentation process and stabilizes the sauce. While still hot, the sauce is bottled for use or distribution. While this is a modernized version of the traditional way to make soy sauce, many popular soy sauce brands you find in supermarkets are made using a faster method. Rather than using aspergillus, they use an acid-hydrolyzed vegetable protein. This allows them to brew soy sauce in just three days rather than the three to six months required by the traditional brewing process.

It is possible to ferment your own soy sauce, which is not too dissimilar a method to the modernized way of making soy sauce. If you're buying it from a grocery store however, we reckon that the absolute best soy sauce brand, Kikkoman.

In Ancient China, many dishes included some type of protein-based sauce that was created through a fermentation process using a meat or fish and a fungus. When Buddhism was introduced to China, this sauce recipe evolved to use soybeans rather than a meat-based protein, creating the ancient predecessor of soy sauce, a fermented soybean paste called jiang or jiangyou. The earliest documentation of a Chinese recipe for making jiang originates from 40 B.C. A Buddhist monk named Kakushin is credited for making the first known version of soy sauce in Japan in 1228, which he made after visiting China and learned how to make fermented miso paste. He discovered that the dregs of that paste created a flavorful liquid that could be used as a sauce or seasoning.

Eventually, this process was refined and the sauce that resulted became known as soy sauce. While each manufacturer may have a slightly different method for making its signature soy sauce, the best ones will include a fermentation process of months or even years in order to create a flavorful sauce. There are five main categories of soy sauce – saishikomi, koikuchi, tamari, shiro shoyu, and usukuchi — and many different types of soy sauce to choose from, each made using a slightly different process.