Is dashi kosher?
Normally no, as the bonito flakes are made of dried tuna. And while tuna is a fish that can be used in a kosher kitchen, the dried bonito flakes that are used in dashi aren’t certified kosher.
And since it’s very hard to make that yourself, and the shrimp or prawn substitute won’t do, you can make it with the grilled skin of whitefish for flavor.
Kosher Bonito Flakes/Katsuo
Chabad Japan seems to indicate that they offer hecschers (rabbinal product certification) to some types of bonito flakes, but I don’t know if that’s still valid or if they import.
There is a recipe calling for using whitefish skin that I’m skeptical of. Rumors indicate that the eden flavored bonitos had previously been made kosher but they lost out on the Cer.
Kosher katsuobushi is quite hard to get, if it weren’t weeks of fermentation you could make it yourself, but that is nigh impossible.
Your best bet is to make a cold brew dashi with just kombu instead of the more traditional bonito dashi.
Kosher Certification on Japanese products
Recently Rabbi Edery and Muto san were in Fukuoka for the Kosher supervision of Nori seaweed for example.
Katsuoboshi is the ”secret” Japanese ingredient used in many Japanese dishes giving it that distinctive Japanese flavor, like in miso soup.
Bonito fish is smoked first then dried for a long period, becomes hard as a rock, and then ”shredded” onto many food recipes.
