Nori (Porphyra spp.)
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Nori (Japanese: 海苔), (Chinese: 海苔; pinyin: hǎitāi, Korean: 김, kim or gim), is the Japanese name for various edible seaweed species of the red alga Porphyra including most notably P. yezoensis and P. tenera. The term nori is also commonly used to refer to the food products created from these so-called "sea vegetables". Finished products are made by a shredding and rack-drying process that resembles papermaking. Japan, Korea, and China are the current major producers of nori, with total production valued at up to US $2 billion per year.
Originally, the term nori was more generic and referred to various kinds of seaweeds including Hijiki. One of the oldest descriptions about nori is dated back around 8th century. In the Taihō Code (大宝律令) enacted in 701, nori was already included in the form of taxation. In Utsubo Story (宇津保物語) written around 987, nori was recognized as a common food. The original nori was formed as a paste, and the nori sheet was invented in Asakusa, Edo (contemporary Tokyo) in Edo period by the method of Japanese papers. The word nori in Japanese has the same pronunciation as nori (糊, glue,) and it is presumed that these plants were also used to glue objects.
Production and processing of nori by current methods is a highly advanced form of agriculture. The biology of Porphyra, although complicated, is well understood and this knowledge is used to control virtually every step of 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 10 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, dark, black, dried sheet of approximately 18 X 20 cm and 3 grams in weight.
Nori is commonly used as a wrap for sushi and onigiri. It is also a common garnish or flavoring in noodle preparations and soups. Nori is most typically toasted prior to consumption ("yaki-nori" in Japanese). A very common and popular secondary product is toasted and flavored nori ("ajitsuke-nori" in Japanese), in which a flavoring mixture (variable, but typically soy sauce, spices and sugar in the Japanese style or sesame oil and salt in the Korean style) is applied in combination with the toasting process. Nori is also eaten by making it into a soy sauce flavored paste noritsukudani (海苔佃煮). In Japan over 600 square kilometres (230 sq mi) of Japanese coastal waters are given to producing 350,000 tonnes (344,470 tons), worth over a billion dollars. China produces about a third of this. 
A related product, prepared from the unrelated green algae Monostroma and Enteromorpha, is called aonori (青海苔 literally blue nori), and is used like herbs on everyday meals like okonomiyaki and yakisoba.