Kombu is a kelp seaweed and the cornerstone of Japanese cuisine, including dashi (Japanese soup stock), sushi rice, and hot pot. It’s also rich in nutrients and umami.
Kombu (昆布) is a seaweed widely consumed in East Asia. Known for its excellent source of glutamate, an amino acid responsible for umami, kombu plays an indispensable role in Japanese cuisine.
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What is Kombu?
Kombu belongs to the brown algae family. It’s primarily used by steeping it in water to extract the natural umami essence, used in many Japanese dishes. It resembles deep olive-colored leaves and is sometimes covered with white powder, also known as glutamic salt.
While making kombu dashi takes minutes, making kombu is a much longer and more rigorous process. Kombu is farm-raised in a nursery where the top leaves are cut off so that the root can regrow. The leaves are then laid out on the rocks to dry, then compressed to release the remaining moisture. Some varieties are further dried indoors to mature. Hokkaido is a major producer of kombu, in fact, cultivates 95% of Japanese kombu.
Types of Kombu
There are different types of kombu, and each has slightly different flavors and textures. Ideally, you would use specific kombu for their characteristics.
Here’s a quick rundown:
- Ma Kombu (真昆布) – thick and wide
- Rishiri Kombu (利尻昆布) – thin and very hard
- Hidaka Kombu (日高昆布) – greenish blackish color
- Rausu Kombu (羅臼昆布) – thin and really wide
1. Ma Kombu 真昆布
Characteristics: 1-8 meters in length, 12-30 centimeters in width. It’s a light brown color with a thick and wide wedge shape. It’s used in the Osaka area and is the most popular type of kombu.
Broth Taste: Refined, sweet, and clear broth
Suggestions: Dashi, clear soup, simmered dishes, hot pot dishes, tsukudani, shio kombu, and tororo komobu
2. Rishiri Kombu 利尻昆布
Characteristics: Narrower and harder than Ma Kombu. The base of the leaf is a thin wedge. More or less ruffled on the margins. The color is dark brown, which also imparts a dark color to the broth, and the leaves are stiff. It is cultivated off the coasts of Rishiri island, in the far northwest of Hokkaido.
Broth Taste: Strong, aromatic, a little salty, and clear broth.
Suggestions: Great for dashi and soups including Hot Tofu (Yudofu), pickling vegetables such as senmaizuke
3. Hidaka Kombu 日高昆布
Characteristics: 2-7 meters in length, 6-15 centimeters in width. Dark greenish and blackish color. It is tender and easy to cook once rehydrated and thus, also eaten in various dishes. Slightly more affordable in price. It is widely used in Tokyo and northern Japan.
Broth Taste: Slightly sweeter than rishiri kombu
Suitable Dishes: Dashi, simmered dishes (nimono), Oden (Fish Cake Stew), non-clear soups, and kombu rolls like Salmon Kombu Rolls
4. Rausu Kombu 羅臼昆布
Characteristics: 1.5-3 meters in length, 20-30 centimeters in width. Thin and wide kombu that hails from the town of Rausu. It’s also used in kobujime (昆布締め), a technique that preserves raw fish or vegetables between kombu sheets and to make kombu tea. It’s called “the king of (kombu) dashi.”
Broth Taste: Rich, soft, fragrant, yellowish, and thick broth.
Suitable Dishes: Great for kombu dashi, simmered dishes (nimono), hot pot dishes, non-clear soups, and Mentsuyu. Rausu kombu loses its flavor after cooking, so it’s not meant for tsukudani or eating.
How to Use Kombu
While kombu dashi is the primary use of kombu, there are many ways of eating kombu.
Kombu Dashi
The primary usage for kombu is to make the Japanese soup stock called Kombu Dashi, which is the base of miso soup, noodle soup, and many other dishes. To make kombu dashi, you reconstitute pieces of kombu by soaking or heating them gently in water (do not boil). To boost the umami, you can add other umami sources such as katsuobushi (bonito flakes), dried shiitake mushrooms, or iriko (dried baby sardines).
Kobujime
Kobujime is a technique where raw fish or vegetables are layered between kombu sheets to impart flavor to the ingredient. At sushi restaurants, you may encounter kobujime of white fish or oily fish like mackerel.
Tororo Kombu
Tororo Kombu is the thin shavings of kombu. It’s rich in flavor and can be eaten with rice balls, as a garnish to Hiroshima-style Okonomiyaki, soba, or udon.
Kombu Tsukudani
Tsukudani (佃煮) is a sweet soy sauce-based simmer of kombu and other umami-rich ingredients that is eaten with rice.
Tsukemono – Japanese Pickles
Small strips of kombu are often added to Japanese pickles (漬物) for additional umami flavor.
Kombu Snack
Kombu pickled in vinegar is called Su Kombu (酢昆布) or eaten as dried shreds (Boro Kombu or Shiraga Kombu).
Recipes Using Kombu
From soup stock, sauces, stews, and vegetable dishes, you can take advantage of the wide range that kombu offers.
Homemade Furikake (Japanese Rice Seasoning)
Kombucha / Kobucha 昆布茶
Kombucha (昆布茶, “kombu tea”) is dried and powdered kombu. Not only can you dissolve the granules in hot water for tea, but I also use this in Unagi Chazuke and many other recipes.
Where to Buy Kombu
You can find kombu packaged in strips. It comes with a thin layer of whitish substance on the surface, which gives the umami. It’s not dust or mold, so don’t wipe off or wash the kombu before use.
You can purchase kombu at Japanese and Asian grocery stores. Whole Foods, gourmet markets, and natural food stores also carry kombu in the Asian food aisle. Alternatively, you can buy good quality kombu from here that ships internationally.
A reader Jessica recommended this Atlantic Holdfast Seaweed Company in Maine that sells different types of seaweeds.
How to Choose the Best Kombu
As mentioned above, the Japanese differentiate the use of kombu for various dishes. If you use kombu daily, it may make sense to buy large bags. Smaller bags with short strips may be convenient if you don’t use kombu frequently.
Buy kombu imported from Japan and check the expiration date. Even though it’s a dried food, it can go bad if it’s not shipped properly, so check that the bag hasn’t been damaged.
How to Store Kombu
Kombu is sensitive to heat, direct sunlight, and humidity. Store opened bags in an airtight container or ziplock bag (I use this OXO container). It’s essential to keep it in a dry, cool, dark place. You can keep kombu for a year. If you have older kombu, check the kombu to see if they are any mold growth. If it looks and smells fine, you can use it as long as it’s less than two years old.
FYI: Seaweed Farming & The Current Trends in the U.S.
In recent years, there have been many fishermen, scientists, and consumers in the west, particularly in the U.S., who see kelp and kelp farming as a solution to environmental sustainability. Once an exotic ingredient to the Americans, kombu kelp has been accepted as a promising source of food, jobs, and a solution to clean ocean waters.
To watch: CBS 60 Minutes reports on seaweed farming and its surprising benefits
Health Benefits
As well as being the best source of glutamate, kombu also contains high levels of iodine, which is essential in a wide range of bodily functions, including metabolism, bone health, and immune response. Kombu is also a great source of dietary fiber and contains several enzymes that can break down complex sugars in the stomach that are usually indigestible.
It’s also rich in minerals and vitamins such as calcium, iron, magnesium, potassium, vitamins A and C, and the trace minerals copper and zinc.
To learn more about the surprising health benefits, read Discover Seaweed: The Essential Ingredient of the Japanese Diet.
Note: You might see a Prop 65 warning label on the kombu product. Kombu doesn’t cause cancer specifically; however, seaweeds (kombu, nori, hijiki) grown in Japan are harvested in water containing high traces of heavy metals than seaweeds harvested elsewhere. Some health agencies have especially issued warnings against consuming hijiki, which contains a higher amount of inorganic arsenic than other seaweed. But there is no ban elsewhere on hijiki or any other seaweed. All kombu contain traces of organic arsenic, but not in harmful quantities, unless you consume more than the usual amount of kombu daily. In California, companies must label a Prop 65 warning on their products.
Kombu for Vegetarian & Vegan Cooking
As it joins the rank of a superfood, many vegetarians and vegans are starting to incorporate kombu kelp and other seaweeds in their cooking.
Did you know the amino acids found in kombu can help break down heavy starches in food like dried beans? This allows for easy digestion and helps minimize the gas-producing effects of beans. It is especially great news for vegetarians and vegans as beans are one of the main food groups.
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