The Japanese Archipelago supports a diversity of marine life and abundant seafood for the people of Japan. Seaweeds* make up a significant component of their diet. Of the many types of seaweed consumed, the most common is nori, a variety of red algae (Rhodophyta, genus Porphyra). Nori is well known as the outer wrap on many types of sushi (see Photos 1 & 2). Nori also covers onigiri (rice balls) and serves as a seasoning on rice, in soups, etc. Porphyra is eaten elsewhere in Asia; in Ireland it is known as ‘laver’.
Nori has been an important food in Japan for at least 1300 years. It was listed in the earliest book on Japanese governance, the ‘Taiho Ritsuryo’ (701 AD), as one of the products that could be used to pay taxes. At that time and for the next millennia, nori was produced in a paste-like form. Modern ‘sheet’ nori was first created in the early 18th century, based on a form of paper making technology (Photo 3). The Asakusa District of Tokyo was the center of nori production.
For most of this history, nori was harvested from wild seaweed. Nori grows on rocks, shells and wood in shallow waters and the intertidal zone (that area of the shore that is periodically covered and uncovered by the tides). It grows best in bays near the mouth of rivers. Nori from Tokyo Bay, and particularly from the Asakusa District, was highly prized. When the capital was moved from Kyoto to Tokyo at the start of the Edo Period 1603-1868 (Tokyo was then known as Edo), the population of Tokyo grew, and much of the shoreline was reclaimed. Thus began the cultivation of nori – initially on sticks and poles sunk into the bottom of shallow waters, later on nets attached to poles, and finally into the large systems of floating nets commonly used today (see Photo 4, and Part II coming in May).
For more than two centuries, nori farmers put out their poles and nets as substrate in early fall to collect the nori spores (referred to as ‘seeding’, although spores are not actually seeds). The spores grow into a leaf-like ‘thallus’ (the body of a seaweed) that is harvested as nori from December to April. Unfortunately, some years produced very little nori, and farmers were unable to develop more reliable methods. This problem became worse after World War II as the waters became increasingly polluted from agricultural runoff.
A British scientist, Kathleen Drew-Baker, made a critical discovery in 1949 that revolutionized nori farming. Dr. Drew-Baker studied the life cycle of an Atlantic species, Porphyra umbilicalis. She found that nori has three distinct stages (or generations); one of these – the conchocelis stage – grows on oyster shells and similar substrate (see Photo 5). The current use of oyster shells to collect the conchocelis stage and use them to ‘seed’ nets has enabled nori farming to grow into a billion dollar industry. Dr. Drew-Baker is honored each year on April 14th, as ‘the mother of the sea’, at a shrine on Kyushu Island, the most productive area of nori grown today (see Photo 5).
Reiko and I visited modern nori farms and factories on Bouze Island last September, October and December to observe and photograph the ‘seeding’, cultivation, harvest and processing of nori. Next month I have an appointment to visit a factory that cultures the conchocelis stage. I will report on these modern methods in Nori – Part II (to be posted in May). In February, my family participated in a nori workshop at the Toba Sea-Folk Museum. We learned the traditional methods used to process freshly harvested nori into sheets, and enjoyed our 55 sheets back home in Kyoto (see Photo 6).
Traditional Nori Processing
Mr. Hiraga, a curator at the Toba Sea-Folk Museum, led the workshop. He provided us with freshly cut nori from nearby Toshishima (Toshi Island) off the coast of Toba City. We used the susabi nori variety (Porphyra yezoensis), which has mostly replaced the original asakusa nori*** (Porphyra tenera). Nori begins to grow in the early fall as a simple, leaf-like structure without any midrib or veins. Harvesting begins in December. Nori is cut off of the net or stick it grows on, leaving a portion of the seaweed behind to regrow. The harvest continues into the early spring, although earlier cuttings produce higher quality nori. Before we started, our instructor gave us a quick introduction to nori and offered some fresh nori to eat (Photos 7 & 8).
Nori processing consists of four steps:
- Rinse fresh nori and put into a strainer
- Chop the nori with a knife into fine pieces
- Place chopped nori into a frame on a bamboo mat in a bucket of water to create a sheet; remove the frame, mat and sheet of nori from the water
- Put the bamboo mat with sheet of nori onto a rack to dry in the sun
The fresh nori had been placed in three large bamboo strainers. There were five adult and four kids in the class, plus Mr. Hiraga. We used colanders to rinse the nori, and then placed it back in the large strainers (see Photos 9 & 10, and Videos 1 & 2).
It took us about 30 minutes to chop the nori. Marina and Ami were enthusiastic, after given a safety talk on how to use a knife (not much previous experience). Other kids were chopping with their parents. One couple had participated before and they used two knives at a time, a technique Reiko tried (see Photo 11 and Video 3).
We took the chopped nori outside to make sheets of nori. A pair of bamboo mats were placed between two wooden frames, and placed in a large tub of water (Photos 12 & 13).
The frames and mats were held just below the surface of the water, while chopped nori was added on top of the mats and within the frame. The nori, mats, and frames were gently moved from side to side to create an even layer of nori, then lifted from the water and tapped twice on the side of the tub to remove excess water (see Photos 14 & 15).
Finally, the upper frame was lifted off and the upper bamboo mat with its sheet of nori was placed on a scaffold to dry in the sun (see Photos 16 & 17 and Video 4). The lower frame and mat were re-used; a fresh mat was placed on top, followed by the top frame, and more nori was added to make the next sheet.
We made 55 sheets in about two hours. We all rinsed and chopped. Marina and Ami made the sheets and Reiko hung them up to dry. Historically, nori farmers would begin this process at 2:00 AM to prepare a large batch of nori and hang it up at sunrise so it would be dry that night. We left our nori at the museum to dry. It was brought inside over night and put out again the next morning. It was fully dry that afternoon, then sent to us by mail (Photo 18).
Before eating, dried nori needs to be roasted – an open flame or skillet works; factory roasters are used today. We heated up a cast iron skillet and placed a sheet onto the pan for a few seconds on each part of the sheet. The color changes from a very dark red or purple (almost black) to green (see Photos 19 & 20 and Video 5).
Freshly roasted nori is crunchy and delicious. It can be used to roll up fish and seasoned rice into a sushi roll (or other type of sushi, e.g. Photos 1 & 2). At home, people often break a sheet into smaller pieces for seasoning, or to wrap up rice and other food. Onigiri is a type of rice ball, usually with some added fish, plum, or kelp, and a nori wrapper. It can be made and eaten at the table, or packed for lunch (see Photos 21 & 22 and Video 6). Our girls enjoy making and eating onigiri!
Coming next: Earth Day Part II – a report on the day’s event at the Miyako Ecology Center, followed by Nori Part II, Modern Cultivation
* ‘Seaweeds’ is a term used for three diverse groups of plant-like organisms. Like plants, they use the sun’s energy to convert water and carbon dioxide into sugars and oxygen (i.e. photosynthesis). They differ from true plants (Kingdom Plantae) in their evolutionary history and structure. Their different photosynthetic pigments give rise to the common names for these three groups: greens (Chlorophyta), reds (Rhodophyta) and browns (Phaeophyta). The term ‘algae’ is a broader term that includes these multicellular seaweeds, as well as other unicellular organisms. For another example of seaweeds used in Japan see my earlier post on wakame.
*** Asakusa nori was the original nori grown in Tokyo Bay, named after the Asakusa District of Tokyo. It has a reputation of exceptional quality, but no longer grows well due to warmer water and pollution. Almost all of the nori grown commercially in Japan today is the susabi nori variety. Wild asakusa nori is reputed to exist in a few refuges in Tokyo Bay and in nearby Ise Bay, but the locations are kept secret. Asakusa nori is available online; a package of 72 sheets costs $300.