Steaming the Soybeans
Soybeans (both spring and autumn soybeans are acceptable) used for brewing soy sauce must first be soaked in water until they swell. The soaking time must be appropriate-enough to allow the soybean protein to absorb water to the maximum extent, but also to prevent over-soaking and souring, which would damage the protein. When soaking, place the soybeans in a wooden bucket or vat, add an equal amount of water, and soak for about 1 hour, until the soybean skins wrinkle. Then pour them into a basket to drain the water, place them in a steamer, and steam for 4-6 hours after the water boils.
Fermentation
After the steamed soybeans have cooled, spread them on bamboo racks and place them indoors for fermentation. The room should be sealed and equipped with several layers of wooden racks for attaching the bamboo racks. The temperature should be above 37℃. If the room temperature is insufficient, charcoal or coal can be added to raise the temperature and promote fermentation. The fermentation time is 6 days. After 3 days indoors, stir the soybeans once to ensure even fermentation. After fermentation, remove the soybeans when yellowish-green Aspergillus and yeast appear on the surface. Pour them into a wooden barrel or vat, add water at a ratio of 100 kg soybeans to 40 kg water, and stir until the soybeans are fully saturated. Drain the excess water, then place the soybeans in a bamboo basket and cover with a cotton cloth. Place the basket in a room at 37-38℃ to continue fermentation for about 8 hours. Stop fermentation when the soybeans feel warm to the touch and have a soy sauce aroma.
Fermentation
Place the fermented soybeans into a wooden barrel or vat (the barrel or vat should be sealable and have an oil drain at the bottom). The fermentation recipe is: 100 kg soybeans, 30 kg salt, and 40 kg water. The specific procedure is to layer soybeans, salt, and water, alternating layers, with the top layer being salt. Then cover the barrel or vat with a lid and seal it with kraft paper.
Oil Extraction
After four months of brewing, the cork at the oil outlet is removed, and the mixture is filtered through a nylon mesh. Then, brine (17 kg of salt per 100 kg of water) is poured into the vat or jar over five days; the liquid flowing from the oil outlet is the soy sauce. Generally, 100 kg of soybeans can produce 300 kg of soy sauce. The resulting soy sauce is usually mixed with syrup. The syrup is made by adding 4 kg of water to 100 kg of sugar and boiling over high heat until it turns dark black, loses its sweetness, and has a slightly bitter taste. 12 kg of sugar is used per 100 kg of soy sauce. The filtered syrup is then mixed in.
Sun-drying
The soy sauce is stored in vats and placed in the sun to dry for 10-20 days before being sold. However, it's important to note that during sun exposure, the container can be left outdoors at night on sunny days to receive dew; on rainy days, the container must be covered. Generally, 10 days of sun exposure in summer and 20 days in autumn and winter is sufficient. If maggots are found inside the container or a layer of white mold is found on the surface, it should be removed and discarded.
