Nori and Ao Nori

Nori is the Japanese name for an edible seaweed species of the porphyra algae, known in English as purple or red larva (porphyra yezoensis and porphyra tenera).

In Japanese cooking it is most commonly pressed into thin layers and dried to form the crisp nori sheets used to wrap sushi.


Wild nori has been harvested in Japan and processed into nori sheets for several centuries using a process very similar to making paper. The wild nori would be picked from around the bay areas, washed, cut and mixed with fresh water to form a pulp. This pulp is then poured onto porous screens and pressed until the water drains away. The thin sheets would then be dried in the sun.

This traditional style of nori production remained a small scale localised industry of fishing communities because of a lack of understanding about the complex life-cycle of the porphyra algae. Nobody knew where the spores came from, so there was little control over the whole cultivation process.

Then in 1951 The British scientist Dr Kathleen Drew-Baker of the University of Manchester made the discovery that sparked the development of the nori cultivation industry in Japan when she established that the first phase of the life history of porphyra involves the spores latching on to and germinating on mollusc shells.

She is remembered by a statue erected by the Japanese nori farmers over-looking the sea at Kumamoto.
Today almost all nori is highly cultivated. The porphyra spores are grown on oyster shells which are suspended on ropes in tanks of temperature controlled water at prefectural seeding centers. Once the spores have developed the shells are laid on the bottom of the tanks. Seeding nets are wound around large wooden drum wheels which are turned through the water in the tanks until they are covered in the germinating spores. The seeded nets are then taken out to the bay areas and hung between long bamboo poles, which have been driven into the sea bed, at just the right height above sea level to allow the nets to be exposed to the air for just a few hours each day. After 50 to 60 days the nori is between 15 to 20 cm long and ready for harvesting and processing into sheets.

The nori is washed then shredded in a machine. The cut nori is thoroughly mixed with freshwater, 4 kg of nori per 100 liters. This nori/water pulp is then fed into a machine resembling a paper- making machine which measures it automatically on to wooden frames about 30 cm square into which fit mats of split bamboo and netting screens. About 600 ml of the mixture is fed into each frame and the water drains away through the mats and screens. The frames move along a production line and over a heated surface. The nori sheets on the bamboo mats are then removed from the frames, stacked up and placed into a low temperature oven to reduce the moisture content to about 18%. The bamboo mats are then removed and the finished nori sheets are put together in packs of 10s and bundles of 100s. The total Japanese output of nori is about 7 billion sheets per year which accounts for over 90% of the total worldwide production.

Ao Nori

Ao Nori is the Japanese name for green larva (Monostroma latissimum).

It is cultivated in Japan in the same way as porphyra (above). After harvesting it is washed and then dried into flakes or powder. It is most commonly used as a seasoning, sprinkled on to hot food and appreciated for its fine aroma. Particularly good for seasoning fried food in batter, potato chips and of course tempura.

Please view the items in our Cook Tokyo Shop for a more detailed explanation of each individual product.