Wash soybeans and Soak in water for 12-18 hours or more.
Boil soy Beans: Pressure cooker (Instant pot, etc.): (pressurization about 25-35 minutes) Stove top: 2-4 hours.
When they are soft (easily squashed between your thumb and ring finger),take it off the stove and drain them. Keep the cooking water as you may use it later.
While the soybeans are cooking, crumble the koji and mix it with some of the salt (10% of weight of koji).
Weigh the cooked soybeans and add salt (10% of the weight of cooked soybeans) Squash the beans with the masher (food processor) and allow to cool.
When the soybeans have cooled to below 140°F, add the koji and salt mixture from step 2 and mix well. If the mixture is too thick, add some cooking water to adjust (aim for a texture/softness similar to that of your earlobes). If you add cooking liquid, add more salt to balance the flavor (10%of the weight of cooking liquid added). If you do not mix well here, fermentation will not work and you will not be able to make delicious miso, let's do it 60 times or more.
Shape the mix into balls approximately the size of your fist.
Disinfect the container with alcohol to prevent mold. Push the balls into the fermenting container. Try to push out all the air out by pressing down hard from the top every time you add a ball and level the surface. Fill up to the top.
Put the container in a cool place (under 59℉) for the first month to prevent unwanted microbial activity. This temperature also facilitates the activity of favorable lactic acid bacteria. After the first month, miso can be stored at any temperature between 59-86℉. Examine the surface once every few weeks and remove any surface mold that might have grown
Leave the miso to ferment for about 6 months. The miso is ready when its surface turns slightly glossy and it starts to release unique miso aromas. You should also taste sweet, umami-rich flavors, and the sharp saltiness from when it was made will have disappeared. Remember, 6 months is only a guideline and you can leave it as long as you want until miso turns just as you prefer. To stop the fermentation to keep the flavor consistent, take the miso out of the fermenting container, transfer it to an air-tight container and keep it in the fridge.
