Rinse the fava beans, removing any bad ones
Soak them in one litre of cold water for at least 8 hours
Replace the water, pour into a pan, and simmer gently until the beans are cooked (approximately 45 minutes)
Whilst the fava beans are cooking, spread the rice on a baking tray. I used a white sushi rice, but any type of rice will do.
Bake the rice at 180'C until it is golden brown. This will take about 20 minutes. Ensure you shake the rice regularly for an even colour.,
When the fava beans have cooked, drain them.
Add one litre of water, which has been boiled and then allowed to cool slightly, to the 3 litre jar. Note: The water is boiled to ensure all bacteria is killed, but ensure it has cooled, as if the water is too hot the jar might crack.
Add the salt to the water and stir until dissolved.
Transfer the cooked beans and toasted rice to a 3 litre jar. Mix well.
Once the mixture has cooled to below 40'C, add the koji.Note: If you don't have a thermometer, just wait until the jar no longer feels warm.
Stir well and then cover with a cloth - I used a muslin, which I attached with an elastic band, but you could use a T-Towel and string.
Leave the jar at room temperature for about 4 months; stirring every other day for the first week and then weekly after that.
After 4 months the colour will have darkened and the liquid will taste delicious! To remove the liquid from the solids, strain through a muslin. Squeezing to remove as much liquid as possible.
Pour into a sterilised bottle and then store in the fridge. Use as you would soy sauce.