Here is our attempt at making the all-time favourite Shoyu at home. Fermentation takes approximately 6 months to 2 years. Be careful to stir the mixture daily. Although it is a long and meticulous process of fermenting and filtering the raw ingredients, the sense of achievement will be rewarding, we promise!
Gently wash the soybeans until the water is clear of impurities. This step is necessary to prevent propagation of germs in the later procedures. Now soak soybeans in water for about 16 to 20 hours depending on the temperature. When the soybeans exhibit the following features, it is ready to move on to Step 2.
For cooking with pressure cooker, boil soybeans for 60 minutes and let sit. As an estimate, 1 kg of soybeans corresponds to 3 batches of cooking.For cooking with pot, combine 3 cups of fresh water and soybeans into a pot and bring to a boil. Once the water boils, reduce heat to simmer. Remove bubbles forming on the surface from time to time. Cook for 10 hours or until tender and partially removed from their pods. Replenish water when they reduce.
Drain the water and allow soybeans to cool until temperature drops below 35°C. Once the soybeans are cooled to 35°C, transfer them to a large bowl.
Combine all-purpose flour and koji starter. Sieve using colander and mix well with spoon. Now, mix the ingredients from Step 3 and Step 4. Be sure no excess water is dripping from the soybeans at this point.
The soybeans are now ready for pasteurisation. Transfer them into a koji fermenter for 18-20 hours. The targeted soybean temperature is 35-40°C. Depending on the situation of koji starter, the temperature may exceed 40℃ in several hours after the start of warming. In this case, swiftly remove the soybeans from the fermenter and allow slight cooling.
After about 10-15 hours, use hand gloves to loosen the soybean for oxygenation and remove any lumps. You will realise a sweet scent exhibiting from the mixture. The soybeans will continue to release heat. When they reach 40°C, we will begin the second stage of warming. Transfer the soybeans into the oven.
Arrange and spread the soybeans on a baking tray. Leave them inside the oven and attach a small cloth at the oven door to prevent water droplets from forming. You do not need to turn the oven on. For the second round of warming, keep the temperature above 40℃ for 6 hours. Usually, it takes approximately 45 hours from the start of first warming to the completion of shoyu koji. The optimal temperature for koji starter to propagate is at 35-40℃. Depending on the season, temperature of the room, and the amount of koji starter being used, conditions may differ. Please set the temperature of fermentation device between 32-42℃, and keep watch.
When green soy sauce aspergillus gradually increases, Shoyu koji is complete! Now let's prepare salt water by combining 300 ml of water and 1 kg of salt into a storage jar and shake well. Next, mix Shoyu koji with the salt water to produce moromi. For 1 kg worth of soybeans, use a 4 litre jar.
With the remaining 1.7 litre of water, add to the product in Step 8 gradually. Then, leave the moromi for fermentation for 6 months to 2 years. Stir the mixture daily. When the soybean has completely dissolved, strain the mixture with cheesecloth into bottles for storage. The result is a fruity and aromatic soy sauce.