Tofu (bean curd) (豆腐)
Tofu is a food that's made mainly from soybeans.
Theory of origin, etc.
There several theories regarding its origin, but none of them is definitive. One theory is that tofu is connected with Prince Liu An of Huainan in the former Han period of the second century B.C., and that it was introduced from mainland China. However, it is also said that there were no soybeans used as raw materials in the Han. Another theory is that tofu was introduced into Japan by a Japanese envoy to the Tang Dynasty of China in the Nara period, but it's very possible that tofu was introduced prior to that time.
腐' (fu), a Japanese character that's part of 豆腐 (tofu), meant a soft, elastic thing (which is called natto (fermented soybeans)) by being turned from the original meaning of "maturing meat in the barn"; however, 豆富 or 豆冨 is sometimes used in Japan because it isn't preferred to use a Japanese character of '腐' meaning 'rotten' for food (Japanese tofu is not fermented). Accordingly, tofu is not rotten. The People's Republic of China has foods made by fermenting tofu. Kyoka IZUMI, a novelist who liked tofu, displayed tofu as 豆府 because he was obsessed with cleanliness. Tofu is a very general food in Japanese cuisine, being as an ingredient in miso soup, kasujiru (soup made with sake lees) and one-pot dishes cooked at the table. China, however, has more kinds of tofu than Japan does, and a wide variety of dishes are made there. Tofu is also eaten on a daily basis in the Republic of Korea, Vietnam, Cambodia, the Kingdom of Thailand, Myanmar and Indonesia. In the United States of America, tofu--which has long enjoyed a certain popularity--is now sold at many grocery stores, and the word "tofu" has become common in the English language.
In the "Hundred Delicacies of Tofu" published in 1782, 100 kinds of tofu dishes were introduced, and tofu was familiar in various kinds of literature.
General tofu
Soybeans, which are softened by being soaked in water, are mashed together with water and then boiled. The liquid obtained by squeezing the boiled soybeans is called soy milk. In producing soy milk, a process that involves filtering after boiling is called 'nishibori' (filtering method), while the process of filtering before boiling is called 'namashibori' (filtering method). The kasu (residue) after squeezing is called okara (bean-curd residue).
When bittern (coagulant) is added to the warm soy milk, protein molecules spread in the form of a net as described below, and the soy milk curdles into a pudding-like consistency. The curdled soy milk that is cut and soaked in water is called kinugoshidofu (silken tofu), while the kind that's scooped and put into a container directly without soaking in water is called yosedofu (fresh tofu). The curdled soy milk that's put into a mold lined with a cloth while it breaks down and is drained then turns into momendofu (firm tofu). Furthermore, as an industrial production process, juten dofu (filled tofu) is made through the processes of chilling soy milk, putting the chilled soy milk into a plastic container with a coagulant, and curding it by heating. Juten dofu is superior in storage stability, and certain varieties can be stored for a month.
Currently, tofu is efficiently made from a small number of soybeans due to the mechanized process that has developed with modern industry, and tofu is sold at cheaper prices. Tofu used to be made every day in a shop, and due to its softness it was sold immersed in a water tank to prevent it from breaking apart. Today, tofu is mainly produced in factories and sold in packages.
The chemical aspect
The coagulation of tofu is caused by the gelatinization of soy milk protein by a coagulant. Therefore, tofu has a structure in which many water molecules are contained in the net-like structure of cross-linked protein.
Generally, there is a case in which a gel is formed through cross-linking between an ion of magnesium or calcium and a chain carboxyl group on the side of protein, and a case in which a gel is formed through the change (denaturalization) of the high-order structure of protein by an acid (acid coagulation). In the former, calcium sulfate, magnesium chloride, calcium chloride or magnesium sulfate, etc., is used as a coagulant, and in the latter glucono-delta-lactone is used as a coagulant. Glucono-delta-lactone is used because it gradually changes to an acid (gluconic acid). The gluconic acid is very safe because it's an organic acid of glucose.
In mainland China, gypsum (calcium sulfate) powered and dissolved in the water is used as a coagulant; however, in the Japanese traditional process used since ancient times, bittern resulting from the process of salt production was mainly used. Calcium sulfate, glucono-delta-lactone and so forth are often used as coagulants in modern-day Japan. This production process is also used in Chinese and Korean factories.
The substance generally referred to as bittern mainly consists of magnesium chloride, and was a secondary product co-abstracted with salt when it was drawn from the salt field.
Currently, the bittern--which contains fine magnesium chloride due to the industrial process, is obtained at rock-salt mining places overseas or is abstracted in the process of industrial salt production in and outside Japan--is used in most cases, and it's rare to use bittern that's actually abstracted from a salt field. Because some tofu makers use the word 'bittern' as a generic term for coagulant, one must use the word with care.
Although it was a mainstream practice to use this bittern as a coagulant before the war (calcium sulfate (sumashiko) was used by some makers), it soon became difficult to obtain the bittern because it was designated as controlled goods. Subsequently, there was an accelerated shift to calcium sulfate--which caused a coagulation reaction in a similar manner and was easy to obtain. When compared with magnesium chloride, a main ingredient in bittern, calcium sulfate had a wider zone in which the proper coagulation reaction occurred (being referred to as the strike zone of coagulation) and made it comparatively easy to make high-quality tofu, which was water-retentive and fine. Therefore, along with the trend in mechanization, a shift to calcium sulfate, which was easy to use as a coagulant, was implemented after the war. In the latter half of the 1980s, the taste of tofu made with bittern was again viewed with favor, and now tofu made with bittern is easily available at supermarkets, etc.
The classic production process
Tofu, which enjoyed widespread popularity among ordinary people, as it was used as a subject of rakugo (traditional comic storytelling) and the recipe book "A Hundred Delicacies of Tofu," published in the Edo period, could be made easily by anyone with sufficient experience, because the degree of processing was comparatively low. Consequently, from the Taisho period to the prewar era each town had one tofu maker.
In describe the remote countryside, there was the vulgar proverb, 'Three ri (the old Japanese unit of distance, approximately 3.927 km or 2.44 miles per ri) to a liquor shop, and two ri to a tofu shop.'
As was the case with miso (bean paste), tofu was made communally in each village.
First, soybeans as raw materials are soaked in fresh water overnight (approximately 12 hours). The next morning, the fully soaked soybeans are then mashed and creamed in a stone mill together with a moderate amount of water.
The mashed soybeans are called 'go.'
The go is then placed in an iron pot, a moderate amount of water is added to adjust the concentration, and the go is boiled over firewood. At this time, it's necessary to add a moderate amount of antifoaming agent, which is obtained by adding lime to cooking oil, because the go foams actively due to saponin. The go, once it has fully boiled, is filtered with a cloth, and the resultant soy milk is poured into a wooden pail. A moderate amount of bittern is added to the warm soy milk as a coagulant, and it's stirred with a wooden board called a kai (paddle) (the series of task after the addition of bittern is called "yose," and it's a high point where the workman shows his technique). When the concentration and temperature of the soy milk, the amount of bittern and a moderate degree of "yose" harmonize, the soy milk starts curdling without separation from the water, whereupon it soon transforms into half-curdled or pudding-like tofu. After the half-curdled or pudding-like tofu is placed into a mold lined with a cloth so that it will break down, a lid is set on the mold, a stone weight is placed on the lid and the tofu is drained, thus producing momendofu (firm tofu).
Stone mill
It is said that when soybeans are mashed with a stone mill, only the essential protein and sugar come out in the liquid, and it becomes easy to extract the astringent soybean skins as okara without allowing them to break up. In the industrial production process, soybeans are ground finely with a grinder. It is said that the use of a stone mill lessens the yake (oxidation) of Go.
Iron pot
This is a so-called jigama (goemon-gama), or an iron pot. Because it's boiled over direct heat, the go is easily scorched. This is why it was virtually impossible to make the present-day high concentrations of soy milk using thick, viscous go. The concentration of solid soybean was considered to be approximately seven to eight percent. In the case of present-day tofu, the general concentration of soy milk is ten to thirteen percent because go won't scorch when it's heated with a steam boiler.
Antifoaming agent
Because the saponin contained in soybeans foams intensively when go is boiled, the go will easily boil over. Additionally, since the soy milk extracted from the foamed go is covered with foam in a whipped state, it's impossible to add bittern and properly do the work of yose. Therefore, for a long time it was a general practice for tofu makers to use the aforementioned antifoaming agent ("Tofu Shusetsu (Compilation of Tofu Making Theory)," published in 1872). The antifoaming agent also serves as an emulsifying agent and plays an important role of drawing forth the flavorful ingredients (amino acid in soybean oil, and other ingredients) contained in soybeans by emulsifying the fluid go. On the other hand, tofu made without using an antifoaming agent has also received attention.
Bittern, yose
There are various methods of yose, but a typical method is to do work of 'gathering' ('yoseru' in Japanese) toward the center with a kai while making the soy milk in the pail react with the bittern. At this time, protein molecules react with the bittern and soy milk starts connecting in the form of mesh, as it enwraps the water molecules. In broad terms, the soy milk becomes pudding-like, and ultimately it becomes tofu. Because the soy milk boiled in the iron pot has low concentrations as mentioned above, the net-like mesh structure in which protein molecules connect becomes rough (high concentrations make a fine-mesh net). This is why the net can't hold water sufficiently, and as a result the water is easily separated from it. When making momendofu, water is drained well and very hard tofu is made. Therefore, it's considered that ancient tofu was very hard momendofu, like this.
Tofu was until recently made through this process in mountain-ringed regions and remote islands. This classic production process was confirmed in Tokuyama-mura and Neo-mura, Gifu Prefecture, in about 1980. Meanwhile, hard tofu, which is nowadays made in mountain-ringed regions as a souvenir using high concentrations of soy milk, but this tofu made by a modern process so it's close but not the same.
Soft tofu
Oboro tofu (half-curdled tofu produced in the making of tofu)
Yosedofu (fresh tofu)
Yushi Dofu (fluffy tofu from Okinawa) in Okinawa Prefecture
Kinugoshidofu is soft tofu because a fine protein mesh resulting from high concentrations of soy milk catches the water molecules firmly, and as a result little water is separated.
Each of the above is soft because it's in the state of only curdling soy milk and water is not squeezed out.
Kata-dofu (hard tofu)
As opposed to the general tofu production process, so-called Kata-dofu is made in many places by various methods such as using high concentrations of soy milk, using sea water instead of bittern, etc., so as to be conservable. Kata-dofu is made in areas of heavy snowfall, mountainous areas and remote islands where distribution is inconvenient, and some kata-dofu is hard enough to be bound with a straw rope for carrying.
Tofu with low water content
Shima Dofu (freshly made tofu with Okinawa water) in Okinawa Prefecture
Although this tofu is made by a 'method of namashibori,' and bittern is added to the soy milk while its viscosity is low, the tofu becomes hard because the moisture content is reduced by applying a load for a long time.
The resultant tofu isn't soaked in water because it's hard enough.
Tofu made using concentrated soy milk
Ishi-dofu (hard tofu) in Shiramine-mura, Ishikawa Prefecture
Iwa-dofu (rock tofu) in Gokayama, Toyama Prefecture
Ishi-dofu in the Iya Valley area (Higashi-Iyayama-mura) of Tokushima Prefecture
Itsuki dofu in Itsuki-mura, Kuma-gun, Kumamoto Prefecture
Tofu made using saltwater
Iwaishima ishi-dofu (hard tofu of Iwai-shima Island) in Iwai-shima Island, Yamaguchi Prefecture
Shio-dofu (saltwater tofu) in Goto-retto Islands, Nagasaki Prefecture
Ishu dofu (Ishu's tofu) in Iki City, Nagasaki Prefecture
Itoman dofu (tofu of the Itoman area) in Okinawa Prefecture
Kanso dofu (dried tofu)
The above are cases in which the tofu is salt-dried, freeze-dried or smoke-dried in order to improve its shelf life.
As an example of salt-dried tofu, rokujo dofu (salted tofu) in the Iwanezawa area (Nishikawa-machi, Nishimurayama-gun) of Yamagata Prefecture is representative. Tofu is dried after removing the water content with salt. Shaved pieces are eaten or used for cooking, because this tofu is very hard.
For kori-dofu (frozen bean curd) made by freeze-drying, refer to the article on koyadofu (freeze-dried bean curd).
Iburidofu (smoked tofu) passed down in Yamato-cho, Gujo City, Gifu Prefecture is smoked tofu made by smoking hard tofu for a long time. Sakurakunsei dofu (tofu smoked over cherry chips), which is made in a similar manner, has been passed down in Itsuki-mura, Kumamoto Prefecture.
Yakidofu (grilled tofu)
A browned tofu made by roasting momendofu over a burner
Tofu kasutera (tofu cake) in Akita Prefecture
Tsuto dofu (tofu rolled in a bamboo mat and boiled) in Minamiaizu-machi, Minamiaizu-gun, Fukushima Prefecture
Komo-dofu (tofu rolled in a wooden straw mat called "komo" and boiled) and tsuto dofu in Ibaraki Prefecture
Sumaki dofu (tofu made in the same manner as tsuto dofu) in Okayama Prefecture
Subo dofu (tofu made in the same manner as tsuto dofu)in Kumamoto Prefecture
Tofu preserved in miso in Kumamoto Prefecture
Tofuyo (fermented tofu) in Okinawa Prefecture
Nutrition
Tofu is rich in plant protein. Since its calorie is comparatively low, tofu has become common in cooking as a health food even in the United States and Europe. Due to the production process, tofu is low in fiber.
(=>okara)
Tofu dishes
In the "Hundred Delicacies of Tofu" written in the Edo period, 100 kinds of tofu dishes were introduced, thus justifying the title.
Processed foods of tofu, and related foods
Abura-age (deep-fried bean curd)
Atsuage (thick fried tofu)
Ganmodoki (deep-fried tofu mixed with thinly sliced vegetables)
Yakidofu (grilled tofu)
Koyadofu (kori-dofu (frozen bean curd))
Soy milk
Yuba (bean-curd skin)
Common expressions related to tofu
Tofu is used as an example of something that's very soft.
Clamp into tofu
This expresses an action of driving an iron clamp that holds lumber into soft tofu. This means there is no effect.
Similar expressions are 'nail into nuka (rice bran)' and 'push noren (a short (split) curtain hung at the entrance of a room) with the arms.'
Die by bumping your head on the corner of tofu
Another similar expression is 'die by hanging yourself with udon (Japanese wheat noodle).'
Others
Even if soybeans and bittern aren't used, soft foods in the form of tofu are called 'kawari dofu' (unusual tofu).
Tamago dofu (egg tofu)
Goma-dofu (crushed sesami seeds boiled in water and chilled like tofu)
Annindofu (almond jelly)
Gyunyu dofu (milk tofu)
Godofu (tofu made with kuzu vines) is a local food in the Nagasaki and Saga prefectures
Rakkasei dofu (peanut tofu), jimami-dofu (Okinawa peanut tofu)
In Prague, Czech Republic, cheese made using soy milk instead of milk is sold as 'TOFU.'
In addition to the plain type, several other types-- including smoked varieties--are sold in the cheese sections of supermarkets.
Tofu is called by that name in the United States and England.
The Philippines has confectionery called 'taho,' which is warm tofu with high water content (pudding-like soy milk) and is eaten by dredging tapioca and brown-sugar syrup. People in Philippines have the custom of eating taho before breakfast, and each morning a 'taho seller' carrying taho on a pole goes from door to door. Today, the Philippine taho seller signals with a bugle, just as a Japanese tofu peddler would have done in the past.
There is a legend of a specter in the motif of tofu, which is called Tofu-Kozo (a spirit child carrying a block of tofu).
Although seldom seen today, the tofu seller blow a bugle when carrying tofu on his sales route, mainly in the Kanto region. One tofu peddler in the early Meiji period, who noticed that a bugle blown by a coachman on a stagecoach or a horse-drawn streetcar for safety 'sounded "tofu,"' took up the practice of blowing a bugle too. In the Kansai region, a tofu seller sounded a bell instead of blowing a bugle (in the Kanto region, an ice-cream seller sounded a bell).
Problems encountered by Japanese makers
Most Japanese makers are medium and small companies, and are family-type operations. This is 'considered to be related to the characteristics of tofu, such as requiring delicate technique for making tofu, impossibility of long storage, etc.,' (as excerpted from the website of Zentoren, the Japanese national tofu association). Over the past few years, long-term storage has become possible due to the improvement of packaging techniques (vacuum filling, etc.), and consequently tofu products made by medium and small companies can also be found in convenience stores. As a result, the special sale becomes usual because supermarkets and convenience-store operators have a strong power to determine the price, and a price in a special sale becomes a recommended retail price, which causes a squeeze on management. Moreover, although most of the soybeans used as raw materials are imported from the United States, the production volume of non-genetically engineered soybean raw materials is less than ten percent of the total production volume in the U.S., and the price of those soybeans is approximately three times that of genetically engineered soybeans. Additionally, a squeeze on management is caused by steep price escalation due to the accelerated shift toward the use of crops for bio-fuel under the U.S. Energy Security Policy, and by raising the price of raw materials due to the escalating price of oil as an ingredient in packaging materials, etc. Makers face the challenge of illegal dumping or the disposal expense, because by law the okara yielded in the manufacturing process is treated as industrial waste.