In a pot, boil the soy sauce, cooking sake, mirin and part of the konbu seaweed.
Turn off the heat, add the bonito flakes and the rest of the konbu seaweed, and leave to rest overnight. This is nikiri.
Wash the yuzu and sudachi. Spread them out to dry.
Cut the citrus fruit in half and juice.
It's a lot of sudachi juice. Transfer from the juicer to containers.
When all the fruit are juiced, strain through a sieve to remove the seeds and pulp.
The sudachi juice is a deep yellow. If there's too much sudachi in the ponzu, it will be very sour. If you wait until the sudachi is yellow and ripe it will be fruity.
Yuzu juice is lightly colored and translucent.
After letting it rest overnight, the bonito flakes and konbu seaweed in the nikiri will have sunk to the bottom.
Drain the nikiri through a sieve to remove the konbu seaweed and bonito flakes.
Add the citrus juices to the nikiri.
Use a funnel to transfer the sauce to bottles. The bottles should be sterilized in boiling water and dried completely beforehand. If there's any moisture on the bottles, it may lead to mold growth.
Dry-roast the leftover bonito flakes from making nikiri in a pan and turn it into furikake. The konbu seaweed can be cut up thinly, and simmered with sugar to make tsukudani.
Story Behind this Recipe
Our trees yield a lot of yuzu and sudachi, so I make this every year.
The ponzu sauce will be quite sharp when it's freshly made, but in 2 to 3 months it will become well-rounded and delicious. It will keep in a cool, dark place for about a year.