Soybeans, wheat, salt and water are the main ingredients in brewed soy sauce. Brewed soy sauce begins with a seed mold that acts upon blended soybeans and wheat, mixed with a brine.
Soy sauce is a fermented brew. The introduced seed culture first acts upon the blended soybeans and wheat to encourage the seed mold culture, or the koji. Koji mixed with brine sits in fermentation tanks, forming a mash, which is the moromi. The moromi then ferments for months with the aid of yeasts and lactic acid bacteria.
The subsequent fermentation yields the color, flavor and fragrance of soy sauce. Soy sauce made via the non-brew process potentially contains traces of hydrochloric acid, salt, caramel color and corn syrup for sweetness.