Tokoroten, written in Japanese as ところてん, 心太, 心天, or 瓊脂, is food made by boiling seaweed such as tengusa (Gelidiaceae) and ogonori (Chinese moss) until they melt and produce agar, which is then cooled down until set. Commonly, the agar is then placed in a device called "tentsuki" which squeezes out and cuts the agar into thin, threadlike shapes (like noodles).
Ninety-eight to ninety-nine percent of the entirety consists of water, and the remaining ingredients are mostly polysaccharide (galactan). While tokoroten is a substance in a form of macromolecular gel, it differs from other food such as jelly in that it has a unique texture of the surface feeling somewhat hard when eaten. There is hardly any nutritional value since it is not digested in the intestines, but being dietary fiber, it has the effect of regulating the functions of intestines.
Commonly in the north of Kanto region and in the west of Chugoku region, tokoroten is served with sanbaizu (vinegar, soy sauce and mirin (or sugar) mixed in roughly equal proportions) poured over it, or with sanbaizu poured over it and with mustard; in the Kinki region, muscovado sugar is sprinkled over it when served, and sometimes fruit is served together; in the Tokai region, it is eaten using only one chopstick, usually by pouring sanbaizu over it and adding sesame thereto. In some areas, it is also served with a sauce which is flavored with soy sauce.
Tengusa is dried in the sun and cleansed. This is repeated several times until the tengusa turns white. The tengusa is then stored in a cool dark place for about one year.
The above tengusa is placed in a large pan with enough water to soak the tengusa, and the water is boiled. Once the water boils, the tengusa is cooked on low heat for about one hour.
The tengusa is strained through cloth and the like to remove impurities, and is moved into a container such as a tray.
Once moved into a container, the tengusa is then left for about three hours to lose heat naturally, until set (it tends to fail that the tengusa is cooled in a refrigerator).
Tentsuki is used to squeeze out the tokoroten (if there is no tentsuki, a knife and the like may be used instead to cut the tokoroten into long threads), and tokoroten is ready to be served.
Kanten is made by freeze-drying the tokoroten outdoors.
According to one theory, tokoroten was called "kokorobuto" and given the Chinese character 心太 accordingly. Then it came to be called "kokorotei", and by further extension, "tokoroten"; however, it seems that names such as "kokoroten" and "tokoroten" were already used in the Nara period as is shown by its mention in days gone by in a writing stored in Shoso-in Treasure Repository.
Tokoroten in a Ritual
A record in a mokukan (narrow, long, and thin pieces of wood strung together that were used to write on in ancient times) stored in Shoso-in Treasure Repository shows that in the Nara period, tengusa was sent to the Imperial Court from areas called Miketsukuni (literally, "land of royal provisions"). This record reflects that tengusa was kept as sechiryo (food and drink of events or its expense) and used in sekki gyoji (events of 24 divisions of the solar year) and other events at the Imperial Court of the time.
Haiku (Japanese seventeen-syllable poem)
"Tokoroten" is one of the kigo (season words) for summer in haiku.
Here, under the eaves, tokoroten looks like a waterfall (by Issa KOBAYASHI).
This tokoroten is full of coolness, which must have been made with the water by carried from the Kiyotaki-gawa River (by Basho MATSUO).
Derivative Words and Works, etc. related to Tokoroten
This refers to the style of promotion in which one is pushed out of his position and is advanced automatically, like the way tokoroten is squeezed out.
This applies especially to the case of grand sumo tournament where there is a custom that "there should not be more than five ozeki (sumo wrestler of the second highest rank)"; if new yokozuna (sumo grand champion) and new ozeki come into being simultaneously when there are already five ozeki, this situation is sometimes called "tokoroten-shiki promotion" implicating ironically that "the new yokozuna has become yokozuna by being pushed out of ozeki's position (in spite of insufficient scores) because someone had to move upward in order to avoid having six ozeki."