Nori (海苔) is the Japanese name for edible seaweed species of the red algae genus Porphyra, including P. yezoensis and P. tenera. It is called laver in Wales and other English-speaking countries, though the popularity of sushi in the United States means that the United States is often an exception to this, either referring to the product as "nori" as the Japanese do, or simply as seaweed. 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 Taihō Code enacted in 701, nori was already included in the form of taxation. Local people have been described as drying nori in Hitachi Province Fudoki (721–721), and nori was harvested in Izumo Province Fudoki (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. The original nori was formed as a paste, and the sheet form was invented in Asakusa, Edo (contemporary Tokyo), 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 WWII, when Japan was in need of all food which could be produced. The decline was due to a lack of understanding of the plant's three stage life cycle so 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, 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 Porphyra, although complicated, is well understood, and this knowledge is used to control the production process. Farming takes place in the sea where the Porphyra 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 × 20 cm (7 in × 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 Japanese coastal waters are given to producing 350,000 tonnes (340,000 long 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 (海苔の佃煮).
Nori is sometimes used as a form of food decoration.
A related product, prepared from the unrelated green algae Monostroma and Enteromorpha, is called aonori (青海苔 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.
|Nutritional value per 100 g (3.5 oz)|
|Energy||35 kcal (150 kJ)|
|Dietary fiber||0.3 g|
|Vitamin A equiv.||
|Percentages are roughly approximated using US recommendations for adults.|
Porphyra yezonsi has been found to contain sufficient vitamin B12 to prevent vitamin B12 deficiency in rats. Though Nori has long been considered to be an important source of vitamin B12 for vegans, its vitamin B12 is actually not biologically available to humans. It likely contains cobalamin analogs which block absorption of B12.
However recent studies have shown otherwise, that Nori (Porphyra yezonsi) contains a significant amount of bioactive vitamin B12, not the inactive analogues. 
- Gim (food)
- Laver (seaweed)
- Mekong weed - river algae often eaten in sheets in Laos
- Spam musubi
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- Suria Link Seaplants Handbook
- Nori 海苔 : Sushi Ingredients
- Description and images of cultivation and harvesting
- Nori Dishes(w/video)
- Marutoku Nori: About Nori