Nori Seaweed

Toasting a sheet of nori. 1864, Japanese painting; Wikipedia, Public Domain,


Nori is the Japanese name for edible seaweed species of the red algae genus Pyropia, including P. yezoensis and P. tenera. It is used chiefly as an ingredient (wrap) of sushi. Finished products are made by a shredding and rack-drying process that resembles papermaking. Originally, the term nori was generic and referred to seaweeds, including hijiki. One of the oldest descriptions of nori is dated to around the 8th century. In the Taiho Code enacted in CA 701, when nori was already included in the form of taxation. Local people have been described as drying nori in Hitachi Province Fudoki (ca 721-721), and nori was harvested in Izumo Province Fudoki (ca 713-733), showing that nori was used as food from ancient times. In Utsubo Monogatari, written around 987, nori was recognized as a common food. Nori had been consumed as paste form until the sheet form was invented in Asakusa, Edo (contemporary Tokyo), around 1750 in the Edo period through the method of Japanese paper-making. The word “nori“ first appeared in an English-language publication in C.P. Thunberg’s Trav., published in 1796. It was used in conjugation as “Awa nori“, probably referring to what is now called aonori.


The Japanese nori industry was in decline after WW II, when Japan was in need of all food that could be produced. The decline was due to a lack of understanding of nori’s three-stage life cycle, such that local people did not understand why traditional cultivation methods were not effective. The industry was rescued by knowledge deriving from the work of British phycologist Kathleen Mary Drew-Baker, who had been researching the organism Porphyria umbilicalis, which grew in the seas around Wales and was harvested for food, as in Japan. Her work was discovered by Japanese scientists who applied it to artificial methods of seeding and growing the nori, rescuing the industry. Kathleen Baker was hailed as the “Mother of the Sea“ in Japan and a statue erected in her memory; she is still revered as the savior of the Japanese nori industry. In the 21st century, the Japanese nori industry faces a new decline due to increased competition from seaweed producers in China and Korea and domestic sales tax hikes.


The word nori started to be used widely in the United States, and the product (imported in dry form from Japan) became widely available at natural food stores and Asian-American grocery stores in the 1960s due to the macrobiotic movement and in the 1970s with the increase of sushi bars and Japanese restaurants. In one study by Jan-Hendrik Hehemann, subjects of Japanese descent have been shown to be able to digest the polysaccharide of the seaweed, after gut microbes developed the enzyme from marine bacteria. Gut microbes from the North American subjects lacked these enzymes.


Production and processing of nori is an advanced form of agriculture. The biology of Pyropia, although complicated, is well understood, and this knowledge is used to control the production process. Farming takes place in the sea where the Pyropia plants grow attached to nets suspended at the sea surface and where the farmers operate from boats. The plants grow rapidly, requiring about 45 days from “seeding“ until the first harvest. Multiple harvests can be taken from a single seeding, typically at about ten-day intervals. Harvesting is accomplished using mechanical harvesters of a variety of configurations. Processing of raw product is mostly accomplished by highly automated machines that accurately duplicate traditional manual processing steps, but with much improved efficiency and consistency. The final product is a paper-thin, black, dried sheet of approximately 18 cm x 20 cm (7 in x 8 in) and 3 grams (0.11 oz.) in weight. Several grades of nori are available in the United States. The most common, and least expensive, grades are imported from China, costing about six cents per sheet. At the high end, ranging up to 90 cents per sheet, are “delicate shin-nori“ (nori from the first of the year’s several harvests) cultivated in Ariake Sea, off the island of Kyushu in Japan. In Japan, over 600 square kilometres (230 sq mi) of coastal waters are given to producing 340,000 tons of nori, worth over a billion dollars. China produces about a third of this amount.


Nori is commonly used as a wrap for sushi and onigiri. It is also a garnish or flavoring in noodle preparations and soups. It is most typically toasted prior to consumption (yaki-nori). A common secondary product is toasted and flavored nori (ajitsuke-nori), in which a flavoring mixture (variable, but typically soy sauce, sugar, sake, mirin, and seasonings) is applied in combination with the toasting process. It is also eaten by making it into a soy sauce-flavored paste, nori no tsukudani. Nori is also sometimes used as a form of food decoration or garnish. A related product, prepared from the unrelated green algae Monostroma and Enteromorpha, is called aonori literally blue/green nori) and is used like herbs on everyday meals, such as okonomiyaki and yakisoba.


Since nori sheets easily absorb water from the air and degrade, a desiccant is indispensable when storing it for any significant time.


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