Toast the sesame seeds in a hot, dry pan until golden.
Blend the seeds, koji grains and salt together with the water until completely smooth.
Transfer the mixture to a container and drop it on the counter a few times to get rid of any air bubbles (this ensures the miso ferments evenly).
Cover the container with muslin cloth, secure with elastic or string and leave in a warm place to ferment – the warmer it is the quicker the fermenting process will be. 25°C takes around 5 days, so this is best made in summer if you don’t have a dehydrator.
Taste after 5 days – if you are happy with the flavour, store in the fridge to halt the fermentation process. If you are not in a hurry, you can carry on fermenting as long as you'd like – the best misos are left to age for years.
