The traditional brewing of soy sauce is accomplished in three distinct steps: koji-making, brine fermentation and refining.
1. Koji-making: To begin the process, carefully selected soybeans and wheat are blended under precisely controlled conditions. Next, a proprietary seed mold is introduced, and the mixture is allowed to mature for three days in large, perforated vats through which air is circulated.
2. Brine Fermentation: The resulting culture, or koji, is then transferred to fermentation tanks, where it is mixed with saltwater to produce a mash called moromi. The next, and perhaps most critical step, is allowing the moromi to ferment for several months using osmophilic lactic acid bacteria and yeasts. During this time, the soybeans and wheat are transformed into a semi-liquid, reddish-brown "mature mash." It is this fermentation process that creates the many distinct flavor and fragrance compounds that build the soy sauce flavor profile.
3. Refining: Following the months of moromi fermentation, the raw soy sauce is separated from the solids by pressing it through layers of filtration cloth. The liquid that emerges is then refined, pasteurized and packaged as finished soy sauce.
Producing non-brewed soy sauce is an entirely different matter. Soybeans are boiled with hydrochloric acid for 15 to 20 hours. After most of the amino acid is removed from the soybeans, the mixture is cooled to stop the hydrolytic reaction. The amino acid liquid is then neutralized, pressed through a filter, mixed with active carbon and purified through filtration.
Color and flavor are introduced to this hydrolyzed vegetable protein mixture by adding caramel color, corn syrup for sweetness, and salt. The mixture is then refined and packaged.