Kombu 101: The Seaweed Secret Behind Japan’s Most Delicious Dishes

If there’s one sea vegetable you should always have on hand, it’s kombu, the dried strips of kelp that are an essential component of Japanese cuisine. “Kombu brings umami, that subtle, yet deep savory taste that ties everything together and enhances other flavors without overpowering them,” says Namiko Hirasawa Chen, founder of the Japanese recipe blog Just One Cookbook.

Read on to learn how the wonder seaweed is used in Japanese cooking, how it can deepen the flavor in your favorite recipes, and how to use it to make easy vegan dashi broth at home.

Kombu (or konbu, in Japanese) is the culinary name for several different types of dried edible kelp that are used as a seasoning. It is farmed on ropes in cold sea waters and harvested when the fronds have grown long and thick. The fronds are then cured and dried to develop their flavor and make them shelf stable. Although kombu is primarily thought of as a Japanese ingredient, it is also farmed and used in China, Korea, Northern Europe, and both the Atlantic and Pacific coasts of North America.

Despite being a seaweed, kombu’s flavor is neither fishy nor salty, just deeply savory. That taste comes from its high concentration of glutamates, the amino acids associated with umami, the “essence of deliciousness.” In fact, kombu is the single richest natural source of umami, and it was through studying kombu broth for miso soup that Japanese scientist Kikunae Ikeda identified umami as the fifth basic taste.

Several types of kelp are marketed as kombu. They can generally be used interchangeably, though each has flavor and texture nuances.

This is the classic kombu kelp variety farmed primarily in Japan and the Pacific Northwest. “The four types of kombu farmed in Japan—ma kombu, rishiri kombu, rausu kombu, and hidaka kombu—can be used interchangeably in home cooking,” says Hirashawa Chen. “Hidaka kombu is the most common Japanese type available. Premium types, such as Ma kombu and Rishiri kombu, are more expensive because they’re harvested in limited regions and prized for their high-quality flavor and clarity.”

Closely related to japonica kelp, sugar kelp is primarily farmed for kombu in the North Atlantic (Maine, Canada, and Northern Europe). Sometimes called royal kombu, it is sweeter and slightly less savory than its Japanese cousin.

Oar weed is native to the North Atlantic and primarily farmed for kombu in Northern Europe. It has an earthy, full-bodied, “seaweedy” taste that’s ideal for mimicking the flavor of fish and seafood.

“In Japanese cooking, kombu is the very foundation of flavor,” explains Hirasawa Chen, “Kombu the key ingredient for making dashi, a seasoned stock which serves as the base for countless dishes, including miso soup, udon and soba noodle soup broths, and nimono (Japanese simmered dishes).” Once kombu has been used to prepare dashi stock, it is often repurposed to make soy-simmered kombu (tsukudani), homemade rice seasoning (furikake), and pickles.

But kombu isn’t just for Japanese recipes. A small (3- to 5-inch) piece of kombu added to the cooking liquid can lend an extra element of umami savoriness to rice, pasta, broths, soups, and stews. It’s also a wonderful secret ingredient in risotto and tomato sauces, where it can round out flavors the way Parmesan cheese (another umami-rich food) would.

The white powdery substance that sometimes coats kombu sheets is mannitol, a natural sugar that’s considered a good thing. Some cooks say the powder should be left on the kombu for added umami taste, others say it should be wiped off for more purity of flavor. (In other words, the choice is up to you!)

Adding a strip of kombu to a pot of beans is a well-known macrobiotic technique believed to improve flavor and digestibility. Kombu’s amino acids may help break down fibrous starches as the beans cook. While scientific evidence is limited, the boost in umami flavor is undeniable.

Kombu is sold in sealed plastic packages and is widely available at natural food stores, well-stocked supermarkets, and Asian groceries, which often carry the largest selection.

Pre-cut kombu flakes and strips are increasingly available as a faster alternative for soups, salads and noodle dishes. Just be sure to check the label to make sure the product contains no added salt, oil, or sugar.

Store kombu in an airtight container in a cool, dark, dry place. Generally, it keeps for months or even years past its “best before” date without losing flavor.

One common misconception about dashi is that it has to be made with dried bonito fish flakes. Dashi can also be made with just kombu, using a simple cold brew method.

For a quicker dashi, you can also use heat. “Gently heat the kombu in water and remove it just before it comes to a boil,” Hirasawa Chen advises. “This slow heating draws out kombu’s umami while keeping it clean and savory, without any bitterness.” She emphasizes the importance of not boiling kombu when making dashi. “If the water gets too hot, the kombu releases a slimy texture and an unpleasant bitter taste, which can cloud the clear and delicate flavor of the broth.”

Here are a few quick ways to put your homemade vegan dashi to delicious use.

For a single serving: Heat 1 cup dashi to a simmer in a saucepan. Spoon 2 teaspoons miso paste into a serving bowl, then stir in 1 tablespoon hot dashi. Add remaining dashi, then sprinkle with 2 teaspoons chopped scallions and 1 tablespoon diced firm tofu. Makes 1 cup

Stir 2 tablespoons reduced-sodium soy sauce and 1 teaspoon pure maple syrup into 2 cups dashi. Add 2 cups steamed, cooled vegetables, then chill 30 minutes or overnight. Makes 2 cups

In a medium saucepan combine 2 cups dashi, 1 tablespoon reduced-sodium soy sauce, and 2 teaspoons pure maple syrup. Stir in 1 cup short grain brown rice; cover and bring to boiling. Reduce heat to medium-low and simmer 45 minutes or until liquid is absorbed. Let stand 10 minutes, then fluff and serve. Makes 3 cups