Seaweed: Japan's Underwater Superfood

  • 10 min read
Seaweed: Japan's Underwater Superfood


Seaweed has long been a staple food in Japanese diets, just as it has been in China, Korea, and Taiwan. In recent years there has been a boom in interest in seaweed, many touting it as a “superfood,” a fact long known by Japanese people. Alongside this boom, the word “seaweed” has often been interchanged with the alternative term “sea vegetable,” which might help better capture the variety of plant or plant-like organisms known as “seaweed” that live in the oceans, rivers, and lakes throughout the world.  

What is Seaweed?

Seaweed: Japan's Underwater Superfood

Nomenclature aside, there is no single term that can capture the breadth and variety of seaweeds, or sea vegetables that exist in our world, let alone those used in Japanese cuisine. Some might be more familiar, like noriand kombu, while others might be less familiar and maybe even a little more intimidating, like umibudō and hijiki.

While there are over 10,000 species of sea vegetables or seaweeds throughout the world, there are three common classifications, or phylum, they can fall under: Rhodophyta, or red algae (nori); Ochrophyta, or brown algae (wakameand kombu); and Chlorophyta, or green algae (chlorella and spirulina.)

Among these 10,000 species of sea vegetables, nearly 1,500 can be found in the waters of Japan, 100 of which are used in Japanese cuisine, more than most other countries. Each of these different seaweeds are quite unique and therefore have different applications in Japanese cuisine, emphasizing their flexibility and versatility in the kitchen.


History of Seaweed in Japan

In Japan, people have been consuming seaweeds for thousands of years. In fact, one of Japan’s earliest legal codes, the Taihō Code of 701, stated that some seaweeds (including nori, wakame,and kombu) were an acceptable form of tax payment. They have long been touted for their nutritional and culinary properties, being a rich source of minerals, vitamins, fiber, and even protein (one 3-gram sheet of nori has the same amount of protein as one fifth of a bottle of milk or one fifth of an egg.) This coincided with the spread of Buddhism in Japan, which prohibited the eating of meat, and so is thought to have contributed to the popularity of eating seaweed throughout Japan. Despite this rise in popularity, many forms of seaweed became readily available to the commoners living in the interior of Japan in the 17th century.

Some evidence suggests, however, that the Jomonpeople of early Japan were eating wakameas far back as 14,000 BCE. Somewhere along the line, the centuries long custom of eating seaweed led to a “digestive evolution” in the guts of early Japanese people.

Over time, bacteria from the ocean present in these sea vegetables mixed with the gut bacteria of Japanese people, and in the process began exchanging little amounts of genetic code, eventually leading to a “digestive evolution.”

What this means is that Japanese people have a unique bacterial enzyme that allows them to better digest and therefore better access more of the nutrients in seaweed. Specifically, Japanese peoples’ guts are more readily equipped to breakdown the sugars in seaweed and therefore use it as an energy source.


The Seaweed of Japanese Cuisine

There is a plethora of of seaweed used in Japanese cuisine, and just as many preparations to match, but some believe they can be broken down into three categories: laver - nori; kelp - kombuand wakame; and tengusa, which is a type of red algae used to make agar agar (or kanten in Japanese.)

While this is an over simplification, it helps to gain some insight as to how some seaweeds relate to one another and how they are different.

Kombu (昆布)

Seaweed: Japan's Underwater Superfood

With a known culinary presence dating back to the eighth century, kombuis a staple in the soup stocks of Japan and an essential ingredient in Japanese cuisine. It is a powerhouse of umami due to kombu’s high amounts of glutamate, or glutamic acid, the essence of umami. For that reason, kombuis a key ingredient in making dashi.

In fact, it is thought that the first uses of kombuas a source for soup stock were in the kitchens of Buddhist monasteries, where the rich umami flavor lent itself to the meat-free cuisine that eventually developed into shōjin ryōri.

The main producer of kombuin Japan is the northernmost prefecture of Hokkaido, where the cold waters make it an ideal location for harvesting and drying the long leaves of kelp. Over time, improvements and developments of new drying techniques led to the widespread availability of kombu, where it became a staple in what was known as the Ryukyu Kingdom, now modern-day Okinawa Prefecture. In fact, kombuconsumption in Okinawan households outnumbers that of most other prefectures despite being nearly 1600 km away from its source in Hokkaido.

Seaweed: Japan's Underwater Superfood

Kombu is most often used to make dashibut can also be used in other ways. One popular preparation is to make kombu tsukudani, where strips of kombu are caramelized in a soy sauce glaze until dark and tender, yet still chewy. It can then be used as a filling for onigiri or as a topping for rice or salads.

Kombucan also be found pickled, or prepared fresh as a side for sashimi.Another preparation for kombuis as a tea known as kombu cha, not to be confused with the popular fermented drink, in which strips of dried kombuare steeped in hot water.

Lastly, another use for kombuis as an added ingredient when making beans. It is thought to help reduce the gas-producing qualities of beans or legumes.

Whichever way you use it, kombuis high in calcium and iron, and like other seaweeds, doesn’t lose much of its nutritional value when dried so is a perfect pantry staple.

Nori (海苔)

Seaweed: Japan's Underwater Superfood

Now eaten worldwide, one of the more familiar varieties of seaweed is probably nori, or dried laver. It is most prominently known as an ingredient for wrapping sushi and onigiri, but it was only in the 18th century that the process for drying nori into sheets was invented. The process was derived from that of the papermakers in Edo, or Tokyo. The seaweed, in this case a red algae, is rinsed, strained, and finely chopped before being placed into a wooden frame atop a bamboo mat inside a bucket of water. The frame is then removed from the water and the bamboo mat is placed on a rack to dry in the sun. The resulting sheets of noriare often then roasted, and some are also seasoned. Seasoned nori,or ajitsuke nori, is usually flavored with soy sauce, salt, and/or sesame oil.

This drying process made nori more readily produced and therefore more prolifically cultivated. In fact, during the early Edo Period (1603-1868) the fame of the nori grown in Edo Bay, or modern Tokyo Bay, led to a boom in the cultivation of the laver. At this time, one could look out to the bay and see where it was grown on nets and poles dug into the shallow shoreline. Prior to this, the laver was often harvested off of rocks, shells, wood, and other surfaces where it grew in shallow waters.

Now, however, the Tokyo Bay is far too polluted and warm for the cultivation of nori, but there are some tightly guarded locations where it is still grown, but if you want a taste of that nori it will cost you somewhere around $300 for 72 sheets.

Seaweed: Japan's Underwater Superfood

Dried nori was not only an incredibly delicious culinary invention, it was also a practical one. By wrapping sushi and onigiri in seaweed, one adds flavor to the rice, while also holding the rice together and keeping one’s fingers from getting sticky. It is also believed that the terpenes, organic compounds that have antibacterial properties, in nori help to preserve the food it is wrapped in, i.e. sushi and onigiri.

Aside from in sushi, dried nori is also added to other table seasonings, like shichimi, cut into thin strips to garnish donburiand ochazuke(different rice dishes) or is simply ground into a powder to become aonori¸ the green seasoning often sprinkled atop okonomiyaki, yakisoba,and takoyaki.You can also readily find norisnacks, which have become more popular in recent years, in different shapes and sizes.

While the dried sheets of nori are probably the most familiar to most consumers, nori is still popular as a side dish when made into nori tsukudani. It is created similarly to kombu tsukudani, where the nori is broken up and mixed with soy sauce, sugar, mirin, and vinegar, creating a past-like dish that resembles what it must have been like to eat nori prior to the invention of the dried sheets.

Hijiki (鹿尾菜)

Seaweed: Japan's Underwater Superfood

Hijikiis a type of seaweed that grows along the rocky shorelines of Japan, where it can often be torn free by waves or weather and left to float about the ocean. It is both cultivated and harvested, cut free by divers from shoreline rocks in the spring during low tide. In order to reap the mineral rich goodness of hijiki,one must first rehydrate it from its dried form before adding it to soups or stews.

Seaweed: Japan's Underwater Superfood

More popularly, however, it is combined with thin strips of aburaage, or fried tofu, soy beans, julienned carrots, renkon, or lotus root, and konyaku before reducing in a sauce of dashi, mirin,sugar, and soy sauce. Despite being rich in calcium, iodine, and magnesium, hijikialso contains potentially harmful levels of inorganic arsenic, so much so that the food agencies of U.S., U.K., and Canada have advised against eating it. That being said, the Japanese government has said that the average Japanese person consumes 0.9 grams per day, while the recommended daily limit is 4.7 grams, so moderation is key. 

Wakame (わかめ)

Seaweed: Japan's Underwater Superfood

Benefiting from the cold, mineral-rich arctic currents around Japan, wakame is another variety of seaweed that has a long history in Japanese cuisine. It is a salty, mildly sweet seaweed with all of the lovely brininess of the sea. Wakame is often dried, but can be available fresh, and is added to soups, most notably misosoup, as well as salads or sunomono, pickle dishes.

Seaweed: Japan's Underwater Superfood

When preparing wakame, it is recommended that the leaves be first cut into small pieces before soaking as they will expand quite a bit. When rehydrated, they gain a satisfyingly light crunch, making wakame a great addition to other vegetables. An easy, yet delicious preparation is to dress wakamewish roasted sesame seeds, soy sauce, and vinegar.

Kanten (寒天培地)

Seaweed: Japan's Underwater Superfood

Maybe one of the least recognizable of the seaweed so far (and probably the least recognizable as having been made from seaweed) kanten, or agar agar, is an essential ingredient in Japanese confectionaries. Made from a red algae known as tengusa, kanten is the final product of a long, time consuming production process. The seaweed is first painstakingly dried before being boiled and liquefied. The resulting broth is then left to solidify into a jelly-like substance known as tokoroten. These jelly-like bricks are then left outside in the winter months to be repeatedly frozen and then thawed over a two-week period to remove excess moisture.

Seaweed: Japan's Underwater Superfood

Tokorotenby itself can be extruded through a specific press to make something akin to jelly noodles, which can be dressed with a brown sugar syrup as the jelly itself doesn’t have much flavor.

Seaweed: Japan's Underwater Superfood

Alternatively, the long bricks of kantencan be grated down into a powder, made into sticks, or even shaved into flakes to be used as a gellifying agent when making confections. Although a little firmer than animal-based gelatins, kantenis a great vegan and vegetarian friendly alternative.

Umibudō (海ぶどう)

Seaweed: Japan's Underwater Superfood

Umibudō,or sea grapes, are a type of sea vegetable particularly popular in Okinawa. As the name suggests, they resemble a cluster of tightly packed mini grapes,but unlike the grapes you may be familiar with, these can be slightly salty, as they capture some of the essence of the sea floor on which they grow. They are usually simply dressed with some soy sauce, vinegar, and mirin, or mixed with a salad.

Seaweed: Japan's Underwater Superfood

Most of all, umibudō offer a nice textural contrast as they have a pleasant pop, bursting in your mouth as you eat them. In Japanese this kind of texture is known as puchi puchi (プチプチ)which is an onomatopoeia meant to convey that little popping sensation.

Arame (荒布)

Seaweed: Japan's Underwater Superfood

Like wakame and kombu, arame is a type of kelp and is used in various side dishes, soups, and salads. Being mild in flavor and smaller than the other kelp, aramecan be quite versatile, but is mostly consumed in Mie and Shimane prefectures as that’s where it is widely cultivated.

In fact, arame is a seaweed seemingly exclusively native to Japan. It’s milder flavor also lends itself to be stir-fried rather than used as a base for soup, and if you’ve ever had konyaku before, along with powdered hijiki, arameis what gives it its grey, speckled color. 

Mekabu (和布蕪)

Seaweed: Japan's Underwater Superfood

Seaweed: Japan's Underwater Superfood


Another addition to the textural sea vegetables, mekabu is actually the flowering portion of the same plant that produces wakame.It has a briny flavor, while maintaining a slight sweetness, and is known for its slimy, in Japanese neba neba, texture. Mekabu is a great topping for rice when dressed with ponzuor a mixture of soy sauce and vinegar, and can also pair well with soups or salads and even makes for a great condiment to go with noodles.

Mozuku (もずく)

Seaweed: Japan's Underwater Superfood

Seaweed: Japan's Underwater Superfood

Like umibudō, mozuku is a popular seaweed from Okinawa, which produces over 90% of Japan’s supply in the March to May harvest season. It is also another of the more neba neba, slimy seaweeds, having a long and stringy texture to boot. The most common way Japanese people eat mozuku is in the prepackaged containers found in stores where it has already been dressed with a vinegar seasoning. Despite this, and its unique texture, Okinawan people can be quite creative with how they use it, even adding it to dumplings (or gyoza), stir-fries, and even omelets.


There are plenty more sea vegetables in Japanese cuisine than I’ve touched on here, but hopefully what you’ve seen will inspire you to incorporate some seaweed into your diet. Whichever you choose, by eating more seaweed you’ll be adding a great source of vitamins and minerals in great supply. Many seaweeds mentioned here are high in vitamins A, C, E and K, which can improve the health of your skin and your hair. They are also high in vitamin D, which helps to promote strong bones. Additionally, sea vegetables are a great source of iodine, which should be noted for those dealing with thyroid issues, as well as DHA, EPA, omega-3’s. and probiotics.

And as intimidating as these sea vegetables might seem, they’re incredibly simple to prepare and are quite delicious. So, give them a try, even if it’s using kombuto make dashi or adding some wakame to a homemade miso soup. In fact, here’s a recipe for kombu tsukudani, or simmered kombu, that doesn’t take more than a few ingredients.It might be just what you need for your entry into the world of seaweed!



About the author:

The spark that lit Kevin Kilcoyne’s interest in Japanese culture began in elementary school through a friendship with his then classmate Keisuke. Since then, that passion has evolved and bloomed to encompass more than just video games and manga, leading Kevin to live in Japan as a participant of the JET program. During his time in Japan, Kevin sought out as many foods as he could, the experiences and taste memories lingering long after they had gone. Now he is forging a path to link his passions for Japanese food, history, and visual culture and is planning for his return to live in Japan once again. For now, you can find Kevin on Instagram (@kevinjkilcoyne) where he posts his photography and illustration work. Keep an eye out for more posts and updates as Kevin delves more deeply into his passions for writing and food.

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