Nori

Nori is a dried edible seaweed used in Japanese cuisine, made from species of the red algae genus "Pyropia" including "P. yezoensis" and "P. tenera". It has a strong and distinctive flavor, and is often used to wrap rolls of sushi or "onigiri" (rice balls).
The finished dried sheets are made by a shredding and rack-drying process that resembles papermaking. They are sold in packs in grocery stores for culinary purposes. Since nori sheets easily absorb water from the air and degrade, a desiccant is needed when storing nori for any significant time.
History.
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 harvesting of nori was mentioned 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. 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 WWII, 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 (bara lafwr or bara lawr), 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.
Production.
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 and 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 of coastal waters are given to producing of nori, worth over a billion dollars. China produces about a third of this amount.
Culinary uses.
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 sometimes also used as a form of food decoration.
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".
Nutrition.
Raw seaweed is 85% water, 6% protein, 5% carbohydrates, and has negligible fat (table). In a 100 gram reference amount, seaweed is a rich source (20% or more of the Daily Value, DV) of vitamin A, vitamin C, riboflavin, and folate (table). Seaweed is a moderate source (less than 20% DV) of niacin, iron, and zinc. Seaweed has a high content of iodine, providing a substantial amount in just one gram. A 2014 study reported that dried purple laver ("nori") contains vitamin B12 in sufficient quantities to meet the RDA requirement (Vitamin B12 content: 77.6 μg /100 g dry weight). By contrast, a 2017 review concluded that vitamin B12 may be destroyed during metabolism or is converted into inactive B12 analogs during drying and storage. The Academy of Nutrition and Dietetics stated in 2016 that nori is not an adequate source of vitamin B12 for humans.
Health risks.
Nori contains toxic metals (arsenic and cadmium), whose levels are highly variable among nori products. It also contains amphipod allergens that can cause serious allergic reactions, especially in highly sensitized crustacean-allergic people. Therefore, daily consumption of high amounts of dried nori is discouraged.