Kombu broth, or dashi, is as quintessential to Japanese cooking as chicken broth is to American cooks. The ingredients are incredibly simple, and the technique for making dashi is much easier than any other broth you can make.
Kombu Is the Key
Japanese dashi is always made with kombu, which is a dried kelp full of glutamic acids. The kombu gives dashi and every dish made from it a rich umami flavor. Kombu can be found at Asian markets and some chain grocery stores. Look for kombu with plenty of the cloudy white crystals over the surface.
A Hybridized Method
Many recipes for dashi insist that kombu should never be boiled, claiming that it will become bitter or slimy.
Truthfully, Japanese cooks make two primary versions of dashi. The first is incredibly delicate and gently simmers the kombu without bringing it to a boil; a second dashi can be made from the same piece of kombu, and this second dashi is boiled for as long as 20 minutes.
The recipe below calls for a hybrid of the two methods. Soaking the kombu overnight releases almost all of the kombu's flavor without concentrating it, while bringing the kombu water to a boil releases some of the kombu's thickening power. The result is a heartier kombu broth, perfect for vegetarian soups.
Learn more: Ingredient Spotlight: Dried Kombu
For Vegetarian Dashi: Mushrooms, Not Bonito
Another primary ingredient for traditional dashi is dried bonito. Bonito is a dried fish which can be found whole (mostly in Japan) or in flake form, and it provides a ton of salty, earthy flavor for dashi — but it is not vegan- or vegetarian-friendly.
You could simply leave out the bonito and make a true kombu broth, or you can replace the bonito with something equally savory and earthy — like dried shiitake mushrooms. A bonus of using dried mushrooms for making kombu broth is that the mushrooms can be eaten after making the broth. Chop them and add them to miso soup, stir-fries, or even pasta.
Using Kombu Broth in Vegetarian Miso Soup
This vegetarian kombu broth was designed to turn simple miso soup — often served as a side dish — into a stand-alone meal. Save the mushrooms from making this broth and add them with savory red miso and silken tofu to make a richer, heartier version of miso soup.
Vegetarian miso soup: How To Make Miso Soup: The Best Method for Most Home Cooks
And for those who'd prefer to a lighter soup, but still want to keep things vegetarian, use this broth with a combinations of white and yellow miso in classic miso soup.
Classic miso soup: How To Make Miso Soup
How To Make Kombu Broth (Vegetarian Dashi)
Makes about 4 cups
What You Need
(2-inch) pieces kombu
dried shiitake mushrooms (optional)
1-quart or larger saucepan
Measuring cups and spoons
Soak the kombu: Combine the water and kombu in a 1-quart or larger saucepan and soak the kombu for at least 8 hours or overnight.
Bring it to a boil: Place the saucepan over medium-high heat and bring to a simmer. Continue to simmer and then remove the kombu from the water just before it comes to a full boil.
Add the mushrooms and simmer: Add the shiitakes, if using, and let the broth come to a rapid simmer. Continue simmering for about 1 minute.
Steep the shiitake mushrooms: Remove the saucepan from heat and let the shiitakes steep in the broth for 5 minutes more.
Strain the broth: Remove the shiitakes from the broth (save for making miso soup or another recipe). Pour the broth through a fine-mesh strainer set over a large bowl.
Use or store the broth: The broth can be used immediately or refrigerated or frozen.
Storage: The cooled broth can be stored in an airtight container in the refrigerator for up to 1 week or frozen for up to 3 months.