Add <quantity>500<unit>g</unit></quantity> of short-grain white rice to a large bowl

Add <quantity>1.2<unit>L</unit></quantity> of water and stir

Let it soak for 12h to absorb the water

Bring water to a boil in a pot large enough to fit your steamer

Drain the soaked rice to remove the excess of water and transfer it to a bamboo steamer lined with parchment paper

Place the steamer onto the pot with boiling water. Steam for 40m until the rice is tender

Wet 2 clean kitchen towels with cold water and line a wide tray with them. Transfer the steamed rice to the tray

Spread it well to cool down until it reaches <temperature>35<unit>°C</unit></temperature>. Use a probe thermometer

Draw lines on the rice with the spoon and sprinkle with <quantity>2<unit>tsp</unit></quantity> of koji spores

Wrap the rice in the kitchen towels. Keep the probe thermometer to keep track of the temperature

Transfer it to the oven and place a pan of hot water beneath it to ensure humidity. Let it ferment for 12h, monitoring to ensure that it remains between <temperature>30<unit>°C</unit></temperature> and <temperature>40<unit>°C</unit></temperature>

Remove it from the oven and spread on a tray lined with a clean kitchen towel

Draw lines on the rice with the spoon and sprinkle or spray with a little water to maintain the humidity

Place the probe thermometer and fold the towel onto itself

Place the rice in the oven and refresh the add more hot water to the pan

Turn the oven light on

Open the door as needed to maintain the temperature between <temperature>30<unit>°C</unit></temperature> and <temperature>40<unit>°C</unit></temperature> 12-24h. The koji rice will be done when it has a white and fluffy appearance

Remove it from the oven and from the kitchen towel. The koji rice is ready

Store in the refrigerator or freezer. Use it for homemade miso, shoyu, sake, and mirin!