Nori – Japan’s Most Famous Seaweed: Part I, History and Traditional Use

The Japanese Archipelago supports a diversity of marine life and abundant seafood for the people of Japan. Seaweeds* make up a significant component of their diet. Of the many types of seaweed consumed, the most common is nori, a variety of red algae (Rhodophyta, genus Porphyra). Nori is well known as the outer wrap on many types of sushi (see Photos 1 & 2). Nori also covers onigiri (rice balls) and serves as a seasoning on rice, in soups, etc. Porphyra is eaten elsewhere in Asia; in Ireland it is known as ‘laver’.

Sushi Tekkamaki

Photo 1: Tekkamaki – tuna roll sushi – served by Jaime Contreras, Musashi restaurant, Kyoto Station. This style of sushi roll originated with the creation of paper-style nori. Musashi serves their sushi on a conveyor belt, a style known as kaiten sushi.

Sushi Plates

Photo 2: Various sushi with nori wraps (from back to front and left to right): tekkamaki (tuna roll), ikura (salmon roe with cucumber garnish), yamaimo (mountain potato with quail egg), uni (sea urchin roe), tamago (chicken egg omelet), and kazunoko (herring roe).

Nori has been an important food in Japan for at least 1300 years. It was listed in the earliest book on Japanese governance, the ‘Taiho Ritsuryo (701 AD), as one of the products that could be used to pay taxes. At that time and for the next millennia, nori was produced in a paste-like form. Modern ‘sheet’ nori was first created in the early 18th century, based on a form of paper making technology (Photo 3). The Asakusa District of Tokyo was the center of nori production.

Nori Sheets

Photo 3: Ami, Reiko and Marina hold up the nori sheets they made in February. These sheets need to be roasted before eating.

For most of this history, nori was harvested from wild seaweed. Nori grows on rocks, shells and wood in shallow waters and the intertidal zone (that area of the shore that is periodically covered and uncovered by the tides). It grows best in bays near the mouth of rivers. Nori from Tokyo Bay, and particularly from the Asakusa District, was highly prized. When the capital was moved from Kyoto to Tokyo at the start of the Edo Period 1603-1868 (Tokyo was then known as Edo), the population of Tokyo grew, and much of the shoreline was reclaimed. Thus began the cultivation of nori – initially on sticks and poles sunk into the bottom of shallow waters, later on nets attached to poles, and finally into the large systems of floating nets commonly used today (see Photo 4, and Part II coming in May).

Pole & Net Nori

Photo 4: Bamboo poles stuck in shallow water support nets at the surface; nori grows on the nets, Toba Bay, Japan.

For more than two centuries, nori farmers put out their poles and nets as substrate in early fall to collect the nori spores (referred to as ‘seeding’, although spores are not actually seeds). The spores grow into a leaf-like ‘thallus’ (the body of a seaweed) that is harvested as nori from December to April. Unfortunately, some years produced very little nori, and farmers were unable to develop more reliable methods. This problem became worse after World War II as the waters became increasingly polluted from agricultural runoff.

A British scientist, Kathleen Drew-Baker, made a critical discovery in 1949 that revolutionized nori farming. Dr. Drew-Baker studied the life cycle of an Atlantic species, Porphyra umbilicalis. She found that nori has three distinct stages (or generations); one of these – the conchocelis stage – grows on oyster shells and similar substrate (see Photo 5). The current use of oyster shells to collect the conchocelis stage and use them to ‘seed’ nets has enabled nori farming to grow into a billion dollar industry. Dr. Drew-Baker is honored each year on April 14th, as ‘the mother of the sea’, at a shrine on Kyushu Island, the most productive area of nori grown today (see Photo 5).

Life Cycle of Nori

Photo 5: Life cycle of nori (Porphyra spp). The GAMETOPHYTE generation produces the familiar leaf-like ‘body’ (thallus) harvested for nori. A microscopic CARPOSPOROPHYTE generation develops on the GAMETOPHYTE generation and produces carpospores. Carpospores settle onto oyster shells and similar substrate where they develop into a filamentous ‘Conchocelis’ stage (generation). The conchocelis stage produces the conchospores that settle onto shorelines, bamboo poles and nets to produce the GAMETOPHYTE generation, i.e. nori. The conchocelis stage was originally considered a completely separate species, Conchocelis rosea, until Dr. Kathleen Drew-Baker discovered it was part of the Porphyra life cycle. Photod copyrighted and used by permission, with thanks to its creator: Lisa Chen and the Monterey Bay Aquarium Research Institute.

Reiko and I visited modern nori farms and factories on Bouze Island last September, October and December to observe and photograph the ‘seeding’, cultivation, harvest and processing of nori. Next month I have an appointment to visit a factory that cultures the conchocelis stage. I will report on these modern methods in Nori – Part II (to be posted in May). In February, my family participated in a nori workshop at the Toba Sea-Folk Museum. We learned the traditional methods used to process freshly harvested nori into sheets, and enjoyed our 55 sheets back home in Kyoto (see Photo 6).

Workshop Sign

Photo 6: Ami, Marina and Reiko stand proudly in front of their nori sheets (on the drying racks behind them); Toba Sea-Folk Museum’s Nori Workshop.

Traditional Nori Processing

Mr. Hiraga, a curator at the Toba Sea-Folk Museum, led the workshop. He provided us with freshly cut nori from nearby Toshishima (Toshi Island) off the coast of Toba City. We used the susabi nori variety (Porphyra yezoensis), which has mostly replaced the original asakusa nori*** (Porphyra tenera). Nori begins to grow in the early fall as a simple, leaf-like structure without any midrib or veins. Harvesting begins in December. Nori is cut off of the net or stick it grows on, leaving a portion of the seaweed behind to regrow. The harvest continues into the early spring, although earlier cuttings produce higher quality nori. Before we started, our instructor gave us a quick introduction to nori and offered some fresh nori to eat (Photos 7 & 8).

Photo 7: Mr. Hiraga introduced the history of nori and how to process it at the Toba Sea-Folk Museum. He holds sheets of nori in his hands. The frames and mats used to make nori sheets are in front of him on the table. Behind him are large wooden tubs and strainers full of freshly cut nori, and the colanders we used to rinse the nori.


Photo 8a: The freshly harvested nori consists of two-dimensional pieces, a few cm in size. Nori in the wooden strainer, ready to be processed. There were three full strainers for three groups of students. Thus, we processed about the amount of nori shown in this photograph.


Photo 8b: The freshly harvested nori consists of two-dimensional pieces, a few cm in size. A bowl of fresh, unprocessed nori for us to sample. We ate it with ponzu sauce (soy sauce and yuzu – a type of citrus).


Photo 8c: The freshly harvested nori consists of two-dimensional pieces, a few cm in size. The same nori as in 8b with some pieces stretched out on the side of the bowl and a 15 cm ruler for scale.

 Nori processing consists of four steps:

  1. Rinse fresh nori and put into a strainer
  2. Chop the nori with a knife into fine pieces
  3. Place chopped nori into a frame on a bamboo mat in a bucket of water to create a sheet; remove the frame, mat and sheet of nori from the water
  4. Put the bamboo mat with sheet of nori onto a rack to dry in the sun

The fresh nori had been placed in three large bamboo strainers. There were five adult and four kids in the class, plus Mr. Hiraga. We used colanders to rinse the nori, and then placed it back in the large strainers (see Photos 9 & 10, and Videos 1 & 2).

Hiraga Hands Out Nori

Photo 9: Hiraga-san places fresh nori into a colander for Ami to rinse.

Marina Rinses Nori

Photo 10: Marina rinses fresh nori.

It took us about 30 minutes to chop the nori. Marina and Ami were enthusiastic, after given a safety talk on how to use a knife (not much previous experience). Other kids were chopping with their parents. One couple had participated before and they used two knives at a time, a technique Reiko tried (see Photo 11 and Video 3).

Chopping Nori

Photo 11: Hiraga-san demonstrates how to chop nori. A handful of nori was placed on a cutting board and chopped repeatedly to create pieces a few mm in size.

We took the chopped nori outside to make sheets of nori. A pair of bamboo mats were placed between two wooden frames, and placed in a large tub of water (Photos 12 & 13).

Nori Outside

Photo 12: Ami and Marina carry our chopped nori outside where they will make nori sheets.

Mats & Frame

Photo 13a: Materials used to make a sheet of nori include two wooden frames, two bamboo mats and a large tub of water. Here, two bamboo mats rest on top of a wooden frame (beneath the mats) in the water. Marina holds the second frame.

Mats & Frame

Photo 13b: Materials used to make a sheet of nori include two wooden frames, two bamboo mats and a large tub of water. Marina places the second frame on top of the two mats and lower frame, and steadies them to keep the upper mat just below the surface of the water. Next step: add chopped nori.

The frames and mats were held just below the surface of the water, while chopped nori was added on top of the mats and within the frame. The nori, mats, and frames were gently moved from side to side to create an even layer of nori, then lifted from the water and tapped twice on the side of the tub to remove excess water (see Photos 14 & 15).

Nori & Frame

Photo 14a: Chopped nori is poured into the frame to create a sheet of nori. Ami places chopped nori onto the upper bamboo mat while Marina steadies the mats and frames.

Nori & Frame

Photo 14b: Chopped nori is poured into the frame to create a sheet of nori. Ami spreads the nori.

Nori & Frame

Photo 14c: Chopped nori is poured into the frame to create a sheet of nori. Ami continues to add nori and spreads it until the entire frame is filled with a thin layer of chopped nori.

Nori & Frame

Photo 14d: Chopped nori is poured into the frame to create a sheet of nori. Ami continues to add nori and spreads it until the entire frame is filled with a thin layer of chopped nori.

Nori & Frame Outside

Photo 15: Marina carefully lifts the frames and mats with nori from the tub, keeping them all flat. She taps them on the edge of the tub twice to remove water from the nori.

Finally, the upper frame was lifted off and the upper bamboo mat with its sheet of nori was placed on a scaffold to dry in the sun (see Photos 16 & 17 and Video 4). The lower frame and mat were re-used; a fresh mat was placed on top, followed by the top frame, and more nori was added to make the next sheet.

Frame Removed

Photo 16a: Once the sheet of nori is safely out of the water, the upper frame is removed.

Photo 16b: After the upper frame is removed, the upper bamboo mat with sheet of nori is taken to the drying rack. The lower mat and wooden frames will be re-used to make more sheets.

Nori on Dry Rack

Photo 17: Reiko places the fresh sheet of nori on the drying rack.

We made 55 sheets in about two hours. We all rinsed and chopped. Marina and Ami made the sheets and Reiko hung them up to dry. Historically, nori farmers would begin this process at 2:00 AM to prepare a large batch of nori and hang it up at sunrise so it would be dry that night. We left our nori at the museum to dry. It was brought inside over night and put out again the next morning. It was fully dry that afternoon, then sent to us by mail (Photo 18).

Completed Nori

Photo 18: Our dried nori arrived by mail a few days after the workshop. The sheets were somewhat irregular in shape and thickness, but otherwise looked similar to store-bought nori.

Before eating, dried nori needs to be roasted – an open flame or skillet works; factory roasters are used today. We heated up a cast iron skillet and placed a sheet onto the pan for a few seconds on each part of the sheet. The color changes from a very dark red or purple (almost black) to green (see Photos 19 & 20 and Video 5).

Nori in Pan

Photo 19: Sheet nori is roasted before eating. It cooks in a few seconds over an open flame or in a hot skillet, as shown here.

Roasted Nori

Photo 20: Roasted (left) and unroasted (right) sheets of nori.

Freshly roasted nori is crunchy and delicious. It can be used to roll up fish and seasoned rice into a sushi roll (or other type of sushi, e.g. Photos 1 & 2). At home, people often break a sheet into smaller pieces for seasoning, or to wrap up rice and other food. Onigiri is a type of rice ball, usually with some added fish, plum, or kelp, and a nori wrapper. It can be made and eaten at the table, or packed for lunch (see Photos 21 & 22 and Video 6). Our girls enjoy making and eating onigiri!

Smaller Nori

Photo 21: People often use sheet nori in pieces: halves, quarters, eighths, etc. To make smaller pieces, fold a sheet in half with a sharp crease and pull apart at the crease. Fold again for smaller pieces.


Photo 22a: Ami and Marina make and eat onigiri. Each girl has a plate of three rice balls mixed with salmon flakes and a plate of nori sheets ripped in half.


Photo 22b: Ami and Marina make and eat onigiri. Ami places a rice ball onto a half-sheet of nori.

Photo 22c: Ami and Marina make and eat onigiri. She wraps the nori around the rice.


Photo 22d: Ami and Marina enjoy eating their onigiri.

Coming next: Earth Day Part II – a report on the day’s event at the Miyako Ecology Center, followed by Nori Part II, Modern Cultivation

* ‘Seaweeds’ is a term used for three diverse groups of plant-like organisms. Like plants, they use the sun’s energy to convert water and carbon dioxide into sugars and oxygen (i.e. photosynthesis). They differ from true plants (Kingdom Plantae) in their evolutionary history and structure. Their different photosynthetic pigments give rise to the common names for these three groups: greens (Chlorophyta), reds (Rhodophyta) and browns (Phaeophyta). The term ‘algae’ is a broader term that includes these multicellular seaweeds, as well as other unicellular organisms. For another example of seaweeds used in Japan see my earlier post on wakame.

*** Asakusa nori was the original nori grown in Tokyo Bay, named after the Asakusa District of Tokyo. It has a reputation of exceptional quality, but no longer grows well due to warmer water and pollution. Almost all of the nori grown commercially in Japan today is the susabi nori variety. Wild asakusa nori is reputed to exist in a few refuges in Tokyo Bay and in nearby Ise Bay, but the locations are kept secret. Asakusa nori is available online; a package of 72 sheets costs $300.

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About Robert Reavis

I study fish behavior and marine ecology through direct observation while diving. I also teach General Biology, Marine Biology, SCUBA and Scientific Diving at Glendale Community College. This year (2011-2012) I will be in Japan to study Traditional Fisheries and Modern Environmentalism.

8 thoughts on “Nori – Japan’s Most Famous Seaweed: Part I, History and Traditional Use

  1. Thank you! This was amazingly informative and we loved all the photos. My daughter had a homework piece to write and she chose sushi. We then had to research all the different ingredients and explain how they are changed or processed to become part of her favourite food. This has helped us enormously and with the photos it has shown her exactly how her dried sheets of seaweed are made. Thank you!

    Debs and Romy x

  2. Pingback: Adventures of A Wild Food Experimentalist | Fergus The Forager

  3. Pingback: 13 Superfoods and Their Ancient Origins | explorerbri

  4. Hey there just wanted to give you a brief heads up and let you know a few
    of the images aren’t loading correctly. I’m not sure why but I think its a linking issue.
    I’ve tried it in two different web browsers and both show the same results.

  5. Hi Im showing the 5 year olds at my daughters kindergarden tomorrow how to roll their own nori maki. Thanks for your informative pictures , now I can tell them how the seaweed becomes sheets to eat. thanks Jo from Australia

  6. Pingback: The Story of Nori, Part II: Modern Mariculture and Processing* | Glendale Community College Blog

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