This is how to make Rice koji made by using Kojiya Sanzaemon's seed koji.
It is a seed koji with little failure even for beginners.It has strong amylase, a saccharification enzyme, and the power of the enzyme produces a white rice koji that brings out sweetness and deliciousness from the rice.
Tools to prepare for making
※1：Measure the temperature inside the storage room(Styrofoam box) and the rice.
※2：Measure the temperature of the hot water to be put into the plastic bottle. This is not necessary if you have a water heater that can adjust the temperature.
※3：Since the tray containing the rice is placed on top of the plastic bottle that has been laid down, a square plastic bottle is recommended for stability.
※4：Large enough to hold a plastic bottle and tray laying in.
Disinfect your tools
Wash all prepared tools before use.
Keep tools and hands clean by disinfecting them with alcohol as needed during use.
Soak the rice in water
Soak the washed rice in water and put it in the refrigerator for about 10 hours to absorb the water.
Drain the water from the rice
Drain the rice in a colander for about 1-2 hours.
Make an indentation in the center of the rice to ensure even drainage. You can make the rice drain more evenly by mixing the rice several times during the process so that the top and bottom of the rice are swapped.
Warm up the inside of the Styrofoam
Warm the rice in advance so that the temperature in the Styrofoam where the rice is kept is 35-40°C at the start of growth.
Fill a plastic bottle with 50°C water, lay it on the Styrofoam, and lay a bath towel on top of it to warm up the box.
If you place the Styrofoam directly on the floor, the cold air from the floor will cool down the interior of the cabinet, so lay a mat or keep it away from the floor.
Using a steamer, steam the rice for about 40 minutes to make it firmer than the cooked rice you usually eat. If there is still a white core, increase the steaming time while monitoring the rice.
※Rice cooked in a rice cooker cannot be made into koji because of its high water content, so be sure to steam it.
Ideally, the rice should be soft enough to resemble a rice cake when it is twisted and squeezed. ※Be careful not to burn yourself as the steamed rice is very hot.
Cool the steamed rice
Place a hand towel on a tray sterilized with alcohol, and place the steamed rice on the tray. Mix the rice with a wooden spoon as if cutting it, then quickly lower the temperature of the rice to less than 40℃ and spread the rice over the entire tray.
Sprinkle seed koji（Tanekiri）
Sprinkle about 1/3 of the required amount of seed koji over the entire rice from a slightly higher position, and mix evenly and well with clean hands. Sprinkle the remaining 1/3 of the seed koji in the same way and mix.
※Do this quickly so that the temperature of the rice does not drop below 30°C.
Keep the rice with seed koji sprinkled on it warm.
To keep the temperature of the rice from dropping below 30°C, wrap the rice in a towel instead of spreading it on a tray. Place the wrapped rice in a Styrofoam box with the tray, wrap it with a bath towel that has been kept warm in the box, and close the lid.
After starting to keep the food warm, check the temperature inside the cabinet from time to time to keep it at about 35℃. If the temperature inside the box drops, re-fill the plastic bottle with 50℃ hot water to warm up the box.
Incubate and Stir 1st.
After sprinkling seed koji: 20 - 22 hours
As the temperature of the rice reaches about 40°C and the koji mold begins to grow, whitish dots appear on the surface of the rice. To the touch, the rice feels a little hard and a little solid.
Gently loosen the rice chunks, and when the temperature of the rice reaches about 37°C, wrap it in a hand towel or bath towel again and place it back in the Styrofoam.
Check the Styrofoam after caring for the rice so that the temperature of the rice does not exceed 42℃.
If the temperature of the rice does not rise or the temperature inside the chamber falls below 30℃, replace the hot water in the plastic bottle. To prevent the temperature inside the chamber from rising too high, add hot water of 40℃.
Incubate and Stir 2nd.
After sprinkling seed koji: 26 - 28 hours
You will begin to smell a faint sweet aroma from the rice. After the first stirring, the temperature of the koji has risen to almost 40℃ again, so loosen the chunks of rice again to lower the temperature. After spreading the rice evenly on the tray, put it back in the Styrofoam in the same way as the first time.
Check the condition of the box after stirring of it. Maintain the temperature of the box at 30-35℃ so that the temperature of the rice does not exceed 42℃.
If the temperature of the box is below 30°C, replace the hot water in the PET bottle. To prevent the temperature from rising too high, fill the water to 40°C.
Incubate and Stir 3rd.
After sprinkling seed koji: 45-48 hours
The entire rice will be covered with koji mold and will have a sweet aroma.Loosen the rice as you did for the first and second stirring.
If the temperature of the rice is over 40℃, mix the rice quickly to lower the temperature. On the other hand, if the temperature is below 35℃, back the rice to 2/3 of the tray after loosening the koji. Wrap the rice again and put the wrapped rice back into the Styrofoam.
If the temperature inside the box is below 30℃, re-fill the PET bottle with 40℃ hot water. If the temperature of the rice is about to exceed 42℃, take out the bath towel and plastic bottle to lower the temperature inside the box.
After sprinkling seed koji: 45 - 48 hours
When the rice has a strong sweet chestnut-like aroma and the rice sticks together to form a plate, the rice koji is complete (de koji). Once the koji has become plate-shaped, it can be easily loosened by hand, so loosen it gently before using it.
Store koji that is not used immediately in the freezer and use it up within a month.