The soy sauce brewing process involves making "koji," brine fermentation and refining. Making non-brewed soy sauce is an entirely different process that is much more simple and takes significantly less time.
The koji-making process begins by blending soybeans and wheat. Once the two ingredients are thoroughly blended, a seed mold is added, and then the mixture is left to mature for a few days. While maturing, the mixture is contained inside of large, perforated vats that allow air to circulate.
After it matures, the koji is transferred to a fermentation tank where it is mixed with saltwater, resulting in what is known as "moromi." The moromi is then left to ferment for several months using osmophilic lactic acid bacteria and yeasts. It is during fermentation that the mixture begins to resemble finished soy sauce in a semi-liquid and reddish-brown state. Upon completion of fermentation, the raw soy sauce is separated from the solids using a filtration process, and then it is refined and pasteurized.
To make non-brewed soy sauce, simply boil soybeans in hydrochloric acid for 15 to 20 hours. Once the soybeans have been stripped of most of their amino acids, they need to be cooled to stop the hydrolytic reaction. Next, the amino acid liquid is neutralized, filtered, mixed with active carbon and then filtered again. Adding caramel color, corn syrup and salt gives the mixture its color and some of its flavor.