Hard koji miso

[Gauthier]

Hello

I have a question regarding the making of miso paste.
I've tried making sweet miso using the recipe in the book Wild Fermentation but the result still had hard rice grains in it even after some weeks.
So how do you use dried koji rice for miso? Do you soak it first, mix it finely with a food processor, or maybe add some hot water to it, before adding it to the beans? Or did something go wrong in the fermentation process that made the grains stay hard? The miso I made also had a strong yeasty flavour, so I did not eat all of it. Thank you!