Dashi, a fish and seaweed stock that's a key ingredient in Japanese cuisine, is basically impossible to find kosher—but it is possible to make a great cheater version to use in Japanese recipes! You'll need a whole smoked whitefish and kombu—details of where to find them kosher certified below.
Nothing makes me more determined to find a kosher workaround than a key ingredient for a given cuisine that just isn't available in a kosher certified version. You know, like Chinkiang vinegar or kecap manis or oyster sauce. Naturally we will be addressing all of these in the due course of time, by substituting, DIYing, and workaround-ing, respectively. Today we tackle dashi, the Japanese fish and seaweed stock that's a crucial ingredient in many a soup and sauce, including, notably, tempura dipping sauce. Traditional dashi is made with dried bonito (fish) flakes and sometimes other dried small fish and/or dried mushrooms. Basically, all the umami in a soup. I have never encountered kosher bonito, but I did find some super old (like, Geocities old) postings about making kosher dashi with a brilliant substitution: that old deli standard, smoked whitefish. Skeptical, and yet otherwise short of ideas, I tried it and was amazed at the depth and deliciousness of the results. Here's what I do.
Ingredients for kosher dashi
So the first thing you'll need to find is kombu, a sea vegetable. Eden Foods makes OK certified kombu that is sometimes possible to find at Whole Foods usually in the Asian section, at Asian groceries, or online (but check the price, as at the time I'm writing this, it's astronomically more online; you can see it in the photo above). By the way, if you can't source whitefish, you can make a simple broth with just kombu and salt that works in place of dashi, too.
So onto the whitefish: there are a number of kosher brands; Blue Hill Bay is a national one in the US. Look for whitefish at kosher supermarkets, better-stocked deli sections at supermarkets, and at Costco where there is a sizeable kosher community. You won't be using the whitefish meat itself to make the stock, just the bones, head, and tail. So you can make a wonderful whitefish salad with the whitefish you buy! The bigger, the better, but any size fish will work here, as long as it's whole, including the smaller whitefish from the deli.
Removing the meat from the whitefish
Every whitefish I've gotten has come cleaned, meaning that it's very easy to remove the flesh from the bones. You simply lift up the flap (like in the photo above, left) and the meat basically removes itself.
Making and storing dashi stock
To make the faux dashi, you simply boil the kombu and whitefish bones with a small amount of salt until brothy, briney, and slightly reduced. I like to use the steamer basket trick, debuted in my Instant Pot chicken soup post, for easy removal of the seaweed and fish bones, but you can also strain your stock into another large container.
You can of course use your dashi right away, or freeze it for later use. I like to freeze it in larger cubes (this is the mold I use; each cavity holds about ⅓ cup) as well as smaller cubes, which I freeze in a regular ice cube tray. The larger cubes are good for soups and cooking while the smaller ones are perfect to defrost for dipping sauces.
Kosher Dashi Stock (parve-fish)
- 1 large piece kombu seaweed
- skin and bones of 1 smoked whitefish
- 5 cups water
- 1 tsp kosher salt
- Combine the kombu, whitefish bones and skins, salt, and water in a pot. Cover the pot and bring to a boil. Reduce heat to a simmer and cook for 20-30 minutes.
- Strain the stock. Use right away or freeze for later use.