Real soy sauce is cooked, aged, and processed over the course of months. The soybeans, wheat, and water are cooked into a mash. They are then aged for a few days with Aspergillus, a type of fungus, to propagate koji mold. The resulting shoyu koji is mixed with brine and aged for several months. When it has been properly aged, the shoyu koji is pressed, resulting in raw soy sauce. Finally, the raw soy sauce is cooked to adjust color, flavor, and aroma . Light, dark, and thick soy sauces are all based on the same recipe. Extra processing produces different flavors and consistencies.

Read more about the main 3 types of Soy Sauce and their uses at The Spruce Eats