Rice koji is made using Kojiya Sanzaemon's rice seed koji.

This seed koji has a high level of amylase, a saccharifying enzyme, and even beginners have little chance of failure. The enzymes bring out the sweetness and flavor of the rice, resulting in white rice koji.

What you need

*1: Measure the temperature inside the storage facility and the rice.
*2: Measure the temperature of the hot water you put in 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 will be placed on top of the lying plastic bottle, we recommend using a square plastic bottle to make it more stable.
*4: A container large enough to hold the plastic bottle and tray. To prevent the koji mold from being starved of oxygen, make a hole about the size of a 10 yen coin on the side.

The appropriate temperature will vary depending on the season and room temperature, so please adjust as necessary.
It is recommended to keep the temperature lower in summer and higher in winter.

Disinfecting tools

Wash all equipment before use.
While using the product, be sure to disinfect your tools and hands with alcohol or other disinfectants as necessary to keep them clean.

Soaking the rice in water (soaking)

Soak the thoroughly washed rice in water and place it in the refrigerator to absorb the water for about 10 hours.

Drain the rice

Drain the rice in a colander for about 1-2 hours.
Making a depression in the center will help the rice drain evenly. Mixing the rice several times during the process will help the rice drain evenly.

Warming up the storage room (koji room)

The temperature inside the rice insulation cabinet is pre-heated so that it is 35-40°C when the rice starts to grow.
Here, we put 50°C hot water into a plastic bottle, place it in a styrofoam box, and then lay a bath towel on top of it to heat the inside of the box.
If you place the styrofoam directly on the floor, the cold air from the floor will cool the inside of the cabinet, so be sure to place a mat underneath it or keep it off the floor.

Steaming rice (steamed rice)

Use a steamer and steam for about an hour until the rice is a little harder than regular cooked rice. If there is still a white core, keep an eye on it and increase the steaming time.
*Rice cooked in a rice cooker contains too much moisture to make koji, so be sure to steam it.

Take a small amount of rice and crush it until it becomes soft like mochi. *Rice is very hot right after steaming, so be careful not to get burned.

Cool the steamed rice (cooling the steamed rice)

Place a hand towel on a tray that has been sterilized with alcohol or other disinfectant, and then place the steamed rice on top. Mix the rice with a rice scoop, quickly lowering the temperature of the rice to just under 40°C, and spread the rice evenly across the entire tray.

Spreading the koji starter (seed cutting)

Sprinkle about 1/3 of the required amount of koji starter over the entire surface of the rice from a slightly elevated position and mix thoroughly with clean hands. Repeat with the remaining koji starter, cutting it into three batches in total.
*Please work quickly so that the rice temperature does not drop below 30°C.

Keeping deseeded rice warm

Before the rice cools below 30°C due to the outside air, place both ends of the hand towel over the rice to wrap it up. Place the wrapped rice and tray inside the styrofoam, wrap it in the bath towel that was used to keep it warm inside the refrigerator, and close the lid.

Temperature Check

After the warming process starts, check the temperature inside the cabinet from time to time and keep it at around 35°C. If the temperature inside the cabinet drops, refill the plastic bottle with 50°C hot water to warm up the inside of the cabinet.

When the rice temperature reaches about 37-40℃, whitish spots appear on the surface of the rice as the koji mold begins to grow. The rice feels a little hard and clumped to the touch.
Gently loosen any clumps of rice, and when the temperature of the rice reaches about 35°C, wrap it again in the hand towel or bath towel and return it to the Styrofoam.

Temperature Check

After cleaning, check the condition inside the storage unit to make sure the rice temperature does not exceed 42°C.
If the rice does not heat up or the temperature inside the refrigerator falls below 30°C, replace the hot water in the plastic bottle. Add 40°C hot water to prevent the temperature inside the refrigerator from rising too much.
If the rice temperature is over 42°C, remove the plastic bottle or bath towel to adjust it.

You will start to notice a faint sweet aroma coming from the rice. After the first cleaning, the temperature of the koji rises to nearly 40°C again, so you need to loosen the rice clumps again to lower the temperature. Once the rice is spread evenly on the tray, you can return it to the styrofoam in the same way as the first time.

Temperature Check

After cleaning, check the condition of the inside of the storage unit. Keep the temperature inside the storage unit at 30-35°C to prevent the rice temperature from exceeding 42°C.
If the temperature inside the cabinet falls below 30°C, replace the hot water in the plastic bottle. To prevent the temperature from rising too much, fill it with hot water at 40°C.

The rice is covered with koji mold and gives off a sweet aroma. As with the first and second cleaning, loosen the rice.
If the rice temperature is over 40°C, mix it quickly to let air in and lower the temperature. On the other hand, if the temperature is below 35°C, loosen the koji and then move it to 2/3 of the tray. Wrap the rice again and return it to the styrofoam.

Temperature Check

If the outside air is cold and the temperature inside the cabinet falls below 30°C, refill the plastic bottle with 40°C hot water.
On the other hand, if the rice temperature is about to exceed 42°C, remove bath towels or plastic bottles to lower the temperature inside the cabinet.

When you have a strong sweet chestnut-like aroma and the rice has stuck together into a slab, the rice koji is ready (dekoji). The slab-shaped koji can be easily broken down by hand, so gently break it up before using.

If you are not going to use the koji right away, store it in the freezer and use it up within a month.