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update: Nov 25,2009


 The Japanese people have been eating seaweeds such as nori, wakame, and konbu for centuries. Besides the long history, Japanese people also consume a large amount of seaweeds compared to other countries. The nationwide production volume of Nori in 1985 is approximately 90 billion nori sheets; in 1987 is about 97 billion; and in 1988, it soared to 100 billion sheets. Although production plunged to 83 billion in the year 2000, the average yearly production remains at approximately 100 billion nori sheets.
  Surprisingly, nori seaweed in its raw form is rarely known. That’s because the nori cultivation ground in the sea is a special place where it is not easy for most people to go to. Nori belongs to the seaweed plant (Porphyra) or algae that sprout from the seeds that resemble those plants that grow on land surface. Know more about the nori seaweed that are commonly present in your dinner tables.

The origin of the name, Nori

From a strong-accented word, “Nuru-nuru suru” (meaning: slimy or slippery), the term “nuru” was derived and coined the name, “nori”.  In another story, the “no” was pronounced rather differently as “na”, which has 2 meanings: “vegetable” and “fish”, indicating the general description of nori as both vegetable and seafood. Since it was awkward to call it a one-syllable name, “na” was combined with “ri” which means algae, and became “nari”,  which gradually changed to “nori”.

The Beginning of Nori Consumption

During the Yamato Era, approximately, 1,300 years ago, it was recorded that nori was used as payment for tax that continued to be practiced onto the next era. Also, during the Heian Era (Year 794-1185), the Imperial family used to eat rice as a staple food and plenty of nori together with other vegetables as viands. It was during the Edo Period (1603-1867), that nori cultivation was developed for mass production and became available for the general consumption.

How Nori Production Began

Towards the end of the Edo Period, the population has increased and people were looking for different types of food for their dining tables. From the waters of Sumida River that streams down to Tokyo bay, people began to grow nori on rocks and driftwoods. With the surge in demand for nori, people began to discover various ways of cultivating nori.
To enable fishermen to catch more fish easily, they used to erect poles, called “Soda” (made up of tree branches and bamboos bundled together) on the grounds of the shallow sea. When the fishermen noticed nori seaweeds clinging to the bamboo poles, they erected many poles and initiated nori cultivation in the year 1717. “Soda tabi”, the material originally used for nori cultivation was later found to be inefficient because cultivation depended largely on natural process with few amount of seeds that stick to the poles. Presently, synthetic fiber nets were developed and began to cultivate nori using the method of poles with attached nets or the “fixed method” which increased and stabilized nori harvest.

Nori Industry of Gyotoku District

The nori seaweed industry in Gyotoku began in 1821 following the introduction by Mr. Jinbe Omiya (born in 1766, made research and developed cultivation method for nori production). Ever since the mudflats have been found to be suitable to cultivation of nori, nori culture farms have spread to the wide expanse of mudflats along Chiba Prefecture’s Tokyo Bay area.
Nori cultivation in Ichikawa City’s Gyotoku and Minami Gyotoku is relatively new compared to that of neighboring cities of Urayasu and Funabashi. When the government during the Meiji Period (1868-1912) encouraged salt production in the Gyotoku area, it became difficult for the farmers to continue cultivation of nori, as they wanted to. They have resorted to borrowing the fishing grounds of Urayasu and Funabashi to enable them to cultivate nori modestly. The right to own the nori cultivation grounds was acquired after the war.

The Place for Nori Cultivation

The original nori was grown at the shallow sea area that depended largely on the currents of the tide. Before the land reclamation began in 1955, the whole of Tokyo Bay’s Chiba Prefecture area (from Urayasu City – Ichikawa City – Funabashi City – Narashino City – Chiba City – Ichihara City – Sodegaura City – Kisarazu City – Futsu City) was used for nori cultivation. Presently, in the neighborhood of Ichikawa City, only Funabashi City is engaged in nori cultivation. In Ichikawa City, nori is being cultivated along the 494 hectare of Shiohama’s front sea area (380 times the size of Tokyo Dome). 

The best nori cultivation ground is where the nets tied to the bamboo poles are made to float on sea surface and exposed to air through the currents of the tides. To do this, the bamboo poles should not be submerged underwater and about 2 meters depth of sea ground is necessary. Ichikawa City has a wide expanse of fishing grounds that are less than 2 meters deep that contributed to thriving nori cultivation. Currently, the nets are no longer exposed to the air, and the cultivation method has shifted to the process where the nets are left to stay afloat on the sea surface by making the waters sticky. With this method, it has become possible to cultivate nori in deeper sea areas.

Life Cycle of Nori

Nori is a kind of seaweed that sprouts and withers in a span of one year. In the 6-month period of warm climate from spring to the beginning of autumn, the nori spores creep inside the shells such as oysters and spend time to grow into its thread-like form called “filamentous condition”, that are hardly visible to the eyes. In September, when the sea temperature drops to about 23 degrees, the seeds will be dispersed from the shells and will stick to other matters, and begin to grow. The seeds are usually dispersed during a strong tidal current, especially during the morning hours. Gradually, these will grow into visible leaves. When March comes, the spores from the mature leaves are let loose and at the same time begin to wither. When these spores stick to the oyster shells, immediately the filamentous condition will be produced.

Fishermen’s Nori Breeding

In spring the spores that came from the mature leaves are made to creep inside the oyster shells. During summer, inside the tank filled with waters these spores are taken care of, and waits for the seeds to be dispersed when autumn comes. At the time when the seeds are vigorously coming out, these will stick to the nets (Land based cultivation). After about one month, leaves will grow at a size that can be plucked. In between the period, from sticking of the seeds to harvest time, the process of removing unnecessary weeds such as Aosaya and Aonori will begin, and cultivation process similar to farming will be initiated. Nori harvest period is from November to April. Nori that is harvested from November until the end of the year is called “new nori”, which is soft and delectable.

What is Land Based Cultivation?

It is a method of nori cultivation that is stable and not influenced by climate changes.
In a big waterwheel with a diameter of 2 meters, nets that can hold about 100 sheets of nori are twined. Seeds are grown using this waterwheel and a water tank filled with sea water with a temperature of less than 23 degrees. The water tank is filled with sea water cooled down to 20 degrees, the oyster shells that have been cultured one week before will be left suspended in the tank. The oyster shells will be taken out from a very dark condition, and when exposed to light for about 30 minutes, nori seeds will be dispersed and allowed to stick to the nets. Through the rotation of the waterwheel, the seeds will be made to stick to the nets evenly. To determine the evenness and the fixed quantity of nori seeds that have attached to the nori nets, the use of optical microscope and light microscope (light is emitted only when the seeds are attached) will be employed. Nori nets where the seeds are properly attached will be taken off from the waterwheel. These are made to dry in the cultivation tank and cooled until they grow into a strong condition. This will also mean the sprouting of seeds. This breeding process will continue until the round seeds transformed into a hard stick where stiff roots begin to come out. This will take about 3 to 4 hours. After this, the water in the nori cultivation nets will be drained and then placed in a freezer with about minus 20 degrees or lower and will be left for a specified period. When the sea water temperature becomes 23 degrees or lower, the fishing ground will be prepared and begin to place the nets for production.

The Making of Dried Nori

In the past, the grown nori plants attached to the nets are plucked by bare hands, but now these are detached or removed by Nori pet (a machine for removing nori), making the process a lot easier. A rotating cutter cuts out the nori, and at the same time absorbs the sea water that it contains. This is a machine that automatically separates nori from the sea water contents. Recently, a high-speed boat for detaching nori (moniker: submarine) is submerged under the nets, which is considered an effective device for harvesting nori with a high rate of efficiency. The harvested nori on that day will be processed into dried nori.

Process of the Operation

  1. Washing of Nori – Waste matters and other algae that are mixed with the harvested nori will be removed by washing them out. (Present method: automatic washing machine. Past method: washing by bare hands)
  2. Cutting of Nori – After washing, nori will be cut finely, and will be made into a paste form.(Present method: automatic cutting machine. Past method: cutting thinly by knife).
  3. Spreading of Nori paste – In a square board or rack (21 cm x 19 cm), the nori paste is spread evenly. (Present method: automatic nori spreading machine. Past method: cutting thinly by knife)
  4. Drying of Nori – The water that comes with the nori paste will be drained, then dried by hot air at a temperature of about 40 degrees. (Present method: Drying by machine. Past method: Drying in the sun).
  5. Stripping of Nori - After drying, nori sheets are stripped from the rack or board . 1 sheet of nori weighs about 3 grams. (Present method: automatic stripping machine. Past method: stripping from the board/rack by hand)
  6. Packing of nori – 1 pack of nori is made up of 10 sheets that are folded into half and banded together.

About Nori Cultivation

Nori cultivation is said to have began 300 years ago, during the Edo Period, and is believed to have originated in the vicinity of Shinagawa area of Tokyo Bay. 
Nori cultivation took a big leap forward after the Second World War, when the nori filaments or thread-like structures were discovered. In wintertime, nori seeds grow to become leaves, making them ready for harvest season. However, until the filaments of nori was discovered, it was not known how the main breeding variety called Asakusa Nori and Susabinori came into being and how they are bred during summer. In summertime, the nori spores that have perforated the shells grow and transform into filament form.
Approximately during the autumn equinox, just like a thick grapevine bearing fruits, the grown nori seeds will be dispersed to the waters and stick to the enclosed nets, and later will grow into the form of leaves. Ms. Katherine M. Drew, a British Marine Plants scholar, discovered that the thread-like structure or filaments that accumulate inside the shells are actually the nori spores.
In the past, nori cultivation depended on the scarce fishing ground and the natural process, but after this discovery, it has become possible to manufacture nori through artificial cultivation which contributed a more stable production.
Since then, there have been great strides in the development of production technologies, resources, and new varieties. Along with this, production was expanded by utilizing land base facilities that led to the realization of a steady production.
Nori cultivation occurs mainly through the currents of the tideland where the river waters and sea waters cross. Looking at its historical aspect, the extinction of tidal flats due to land reclamation of some coastal areas gives a glimpse of the social demands and struggles that  have transpired at different periods of time. The transformation of the reclaimed coastal areas into fishing grounds had contributed greatly to the sustenance of a stable production with the help of technological advances. However, in 2000, Ariake Sea experienced a poor yield during the harvest season, mainly due to climate changes that cannot be altered by technology. Once again, the major concern that nori cultivation is confronted with is the stability of the environment surrounding the fishing grounds.
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●Information on this page is published by:
Publicity Affairs Section, Planning Department
Ichikawa City Hall
Yawata 1-1-1, Ichikawa City, Chiba Prefecture
電話:047-334-1106 FAX:047-336-2300