Tofu

Tofu (soft, typical)
Nutritional value per 100 g (3.5 oz)
Energy	291 kJ (70 kcal)
Carbohydrates	1.5 g
Fat	3.5 g
Saturated	0.5 g
Protein	21 g
Minerals
Vitamins and minerals
Minerals	Quantity %DV†
Calcium	10% 130 mg
Iron	6% 1.10 mg
Sodium	0% 4 mg
	This sample is relatively rich in calcium due to the coagulant. Values for other varieties may be significantly lower.
	†Percentages estimated using US recommendations for adults, except for potassium, which is estimated based on expert recommendation from the National Academies.

Tofu
	A block of Japanese raw silken tofu
Alternative names	Bean curd
Place of origin	China
Associated cuisine	East Asian cuisine & Southeast Asian cuisine Chinese; Japanese; Okinawan; Korean; Filipino; Indonesian; Malaysian; Singaporean; Thai; Vietnamese; ;
Main ingredients	Soy milk
	Cookbook: Tofu; Media: Tofu;

Tofu (Japanese: 豆腐, Hepburn: Tōfu, Korean: 두부; RR: dubu, Chinese: 豆腐; pinyin: dòufu) is a food prepared by coagulating soy milk and then pressing the resulting curds into solid white blocks of varying softness: silken, soft, firm, extra (or super) firm. Tofu is also known as bean curd in English. Tofu originated in China and has been consumed in the country for over 2,000 years.^[1]^[2] Tofu is a traditional component of many East Asian and Southeast Asian cuisines.^[3] In modern Western cooking, it is often used as a meat substitute.^[4]

Nutritionally, tofu is low in calories, while containing a relatively large amount of protein. It is high and reliable source of iron, and can have a high calcium or magnesium content depending on the coagulants (e.g. calcium chloride, calcium sulphate, magnesium sulphate) used in manufacturing.

Cultivation of tofu, as a protein-rich food source, has one of the lowest needs for land use (1.3 m²/ 1000 kcal)^[5] and emits some of the lowest amount of greenhouse gas emissions (1.6 kg CO₂/ 100 g protein).^[6]^[7]

Etymology

The English word "tofu" comes from Japanese tōfu (豆腐). The Japanese tofu, in turn, is a borrowing of Chinese 豆腐 (Mandarin: dòufǔ; tou4-fu) 'bean curd, bean ferment'.^[8]^[9]^[10]^[11]

The earliest documentation of the word in English is in the 1704 translation of Domingo Fernández Navarrete's A Collection of Voyages and Travels, that describes how tofu was made.^[12] The word towfu also appears in a 1770 letter from the English merchant James Flint to Benjamin Franklin.^[13]^: 73 The term "bean curd(s)" for tofu has been used in the United States since at least 1840.^[14]^[15]

History

Tofu making was first recorded during the Chinese Han dynasty about 2000 years ago.^[1] Chinese legend ascribes its invention to Prince Liu An (179–122 BC) of Anhui province. Tofu and its production technique were introduced to Japan^[16]^[17]^[18] during the Nara period (710–794).^{[citation needed]} Some scholars believe tofu arrived in Vietnam during the 10th and 11th centuries.^[13]^: 305 It spread to other parts of Southeast Asia as well.^[19] This probably coincided with the spread of Buddhism as it is an important source of protein in the vegetarian diet of East Asian Buddhism.^[16] Li Shizhen, during the Ming dynasty, described a method of making tofu in the Compendium of Materia Medica.^[20] Since then, tofu has become a staple in many countries, including Vietnam, Thailand, and Korea, with regional variations in production methods, texture, flavor, and usage.

Theories of origin

The most commonly held of the three theories of tofu's origin maintains that tofu was discovered by Liu An (179–122 BC), a Han dynasty prince. While plausible, the paucity of reliable sources for this period makes this difficult to conclusively determine. In Chinese history, important inventions were frequently attributed to important leaders and figures of the time.^[21] In 1960, a stone mural unearthed from an Eastern Han dynasty tomb provided support for the theory of the Han origin of tofu; however some scholars maintain that tofu during the Han dynasty was rudimentary and lacked the firmness and taste for it to be considered as tofu.^[22]

Another theory suggests that the production method for tofu was discovered accidentally when a slurry of boiled, ground soybeans was mixed with impure sea salt. Such sea salt would probably have contained calcium and magnesium salts, allowing the soy mixture to curdle and produce a tofu-like gel.

The last group of theories maintains that the ancient Chinese learned the method for curdling soy milk by emulating the milk curdling techniques of the Mongolians. The primary evidence for this theory is the etymological similarity between the Chinese term rǔfǔ (乳腐), which literally means "milk curdled", used during Sui dynasty (AD 581–618), for dishes with a consistency like yogurt or soft cheese, later influenced by Mongolian milk products and methods of production, and the term dòufu (豆腐, "beans curdled" ) or tofu. Although intriguing and possible, there is no evidence to substantiate this theory beyond academic speculation.^[21]

East Asia

China

A form of tofu may have been discovered during the Han dynasty (202 BC – AD 220), but it did not become a popular food in China until the Song dynasty (960–1279).^[11]

In China, tofu is traditionally used as a food offering when visiting the graves of deceased relatives. It is claimed that the spirits (or ghosts) have long lost their chins and jaws so that only tofu is soft enough for them to eat. Before refrigeration was available in China, tofu was often only sold during winter since tofu did not spoil as easily in cold weather. During the warmer months, tofu, once made, spoils if stored for more than a day.

Japan

Illustration of a tofu seller (right) and a sōmen seller (left) by Tosa Mitsunobu, from the Songs of the Seventy-one Craftsmen (七十一番職人歌合 Shichijūichi-ban Shokunin Uta-awase), a poetry anthology written around 1500

Tofu was introduced to Japan by Zen Buddhist monks, who initially called it "Chinese curd" (唐腐, tōfu).^[11] A firm variation of tofu was introduced in Tosa Province, today's Kochi Prefecture, by a Korean doctor and prisoner of war following the Japanese invasions of Korea (1592–1598).^[23]^[24]^[25] Much of tofu's early use in East Asia was as a vegetarian substitute for meat and fish by Buddhist monks, especially those following Zen Buddhism.^[11]^[24]

The earliest Japanese document concerning tofu refers to the dish being served as an offering at the Kasuga Shrine in Nara in 1183.^[26] The book Tofu Hyakuchin (豆腐百珍), published in 1782 of the Edo period, lists 100 recipes for cooking tofu.^[27]

Southeast Asia

In Southeast Asia, tofu was introduced to the region by Chinese immigrants from Fujian province, as evidenced by many countries in Southeast Asia referring to tofu using the Min Nan Chinese word for either soft or firm tofu, or "tāu-hū" or "tāu-goaⁿ" respectively. In Indonesia, Malaysia, Singapore, Thailand, Cambodia, Myanmar, the Philippines and Vietnam, tofu is widely available and used in many local dishes.^{[citation needed]}

Tofu is called tahu in Indonesia, and Indonesian dishes such as tahu sumbat, taugeh tahu, asinan, siomay and some curries, often add slices of tofu. Tahu goreng, tahu isi and tahu sumedang are popular fried tofu snacks.^{[citation needed]}

Tofu is called tauhu in Malaysia and Singapore. Malaysian and Singaporean Indians use tofu in their cuisine, such as in Indian mee goreng, and rojak pasembor. Peranakan cuisine often uses tofu, as in Penang curry noodles and laksa. Indonesia, Thailand, Malaysia, and the Philippines are major producers of tofu and have plants in many municipalities.

Tofu in the Philippines is widely eaten as the breakfast snack tahô (soft tofu, from Philippine Hokkien 豆腐 "tāu-hū"), or as tokwa (dry, firm tofu that is usually fried, from Philippine Hokkien 豆干 "tāu-goaⁿ"), which is a staple alternative to meat in main meals and in numerous regional dishes. Tofu was introduced to the archipelago in the 10th to 13th centuries by Song dynasty Chinese mariners and merchants, along with many other foods that became staples of the Philippine diet. The use and production of tofu were first limited to urban centers with influential Chinese minorities, such as Cebu or Tondo, but quickly spread to even remote native villages and islands.^{[citation needed]}

Elsewhere

Benjamin Franklin was the first American to mention tofu, in a 1770 letter to John Bartram.^[13]^: 73^[28] Franklin, who encountered it during a trip to London, included a few soybeans and referred to it as "cheese" from China.^[29] In 1770, Franklin also corresponded with James Flint on the subject of how the Chinese converted callivances (soybeans) into tofu. Flint's writing "Towfu" in his letter is the earliest documented use of "tofu" in the English language.^[13]^: 73 The first tofu company in the United States was established in 1878.^[30] In 1908, Li Yuying, a Chinese anarchist and a vegetarian with a French degree in agriculture and biology, opened a soy factory, the Usine de la Caséo-Sojaïne. This was the world's first soy dairy and the first factory in France to manufacture and sell beancurd.^[31]

However, tofu was not well known to most Westerners before the middle of the 20th century, when it was popularized in the United States by William Shurtleff and Akiko Aoyagi (The Book of Tofu, 1975).^[32]

Production

Making tofu

Coagulated soy curds

Curds in a tofu mold

Regardless of the product or scale of the production, the production of tofu essentially consists of:

The preparation of soy milk
The coagulation of the soy milk to form curds (douhua)
The pressing of the soybean curds to form tofu cakes

It is similar to the production of dairy cheese by coagulating the milk of dairy animals to form curds and pressing and aging the curds to form cheese. Typical tofu-making procedures are cleaning, soaking, grinding beans in water, filtering, boiling, coagulation, and pressing.^[33] There are also types, such as Japanese raw silken tofu, in which the curds are not pressed.^[34]

Coagulation of the protein and oil (emulsion) suspended in boiled soy milk is the most important step in the production of tofu. This process is accomplished with the aid of coagulants. Coagulation depends on complex interactions. There are many variables including the variety and percentage of protein in the soybeans used, slurry cooking temperature, coagulation temperature, and other factors.^[35]

Soybean proteins are mainly composed of 7S and 11S proteins. The negative surface charges on these globulins usually cause them to repel each other. Heating soy milk denatures the proteins and exposes hydrophobic groups normally oriented toward the inside of the globulin structure. Cations from coagulants bind the negatively charged groups.^[36] As the net charges of the protein molecules are neutralized, attractive hydrophobic interactions dominate over repulsive electrostatic charges, and protein aggregates are formed.^[37]

Two types of coagulants (salts and acids) are used commercially.^[38]

Salt coagulants

Tofu tools

Dubu-teul ('tofu mold') from Korea

Dubu-kal ('tofu knife') from Korea

Calcium sulfate (gypsum) (Chinese: 石膏; pinyin: shígāo) – the traditional and most widely used coagulant to produce Chinese-style tofu, it produces a tofu that is tender but slightly brittle in texture. The coagulant itself is tasteless. Also known as gypsum, calcium sulfate is quarried from geological deposits, and no chemical processing or refining is needed, making it the cheapest coagulant used in tofu production. When used in production, the coagulation reaction is slower due to its low solubility, forming a smooth, more gelatinous tofu with relatively high water content and soft texture.^[33] Use of this coagulant also makes tofu that is rich in calcium. As such, many tofu manufacturers choose to use this coagulant to be able to market their tofu as a good source of dietary calcium.^{[citation needed]}
Chloride-type nigari salts or lushui (Traditional: 鹵水, 滷水; Simplified: 卤水; Pinyin: lǔshuǐ) – Magnesium chloride and calcium chloride: Both of these salts are highly soluble in water and affect soy protein in the same way, whereas gypsum is only very slightly soluble in water and acts differently in soy protein precipitation, the basis of tofu formation. These are the coagulants used to make tofu with a smooth and tender texture. In Japan, a white powder called nigari, which consists primarily of magnesium chloride, is produced from seawater after the sodium chloride is removed and the water evaporated. Depending on its production method, nigari/Lushui may also contain small quantities of magnesium sulfate (Epsom salt), potassium chloride, calcium chloride, and trace amounts of other naturally occurring salts. Although the term nigari is derived from nigai, the Japanese word for "bitter", neither nigari nor pure magnesium chloride imparts a perceivable taste to the finished tofu. Calcium chloride is not found in seawater in significant quantities and therefore is not regarded as nigari. It is used extensively in the United States due to its flavor and low cost.^[13]^: 73^[39] Fresh clean seawater itself can also be used as a coagulant.^[40]

Acid coagulants

Glucono delta-lactone (GDL): A naturally occurring organic acid also used in cheesemaking, this coagulant produces a very fine textured tofu that is almost jelly-like. It is used especially for "silken" and softer tofus and confers a faint sour taste to the finished product.^[41] GDL is derived from glucose and takes the form of a white powder at room temperature. Its molecular structure contains a six-membered heterocyclic ring that is hydrolyzed upon contact with water, slowly converting GDL to gluconic acid.^[42] When added to soy milk, it gradually lowers the pH and causes proteins to coagulate evenly throughout the mixture,^[43] forming a single, smooth gel that is free of air gaps and that resists breaking during transportation. Using GDL as a coagulant, silken tofu can be formed directly in its container, as it does not require pressing.^[44] This acid coagulant is also commonly used together with calcium sulfate to give soft tofu a smooth, tender texture.
Other edible acids: Though they can affect the taste of the tofu more, and vary in density and texture, acids such as acetic acid (vinegar) and citric acid (such as lemon juice), can also be used to coagulate soy milk and produce tofu.^[45]

Enzyme coagulants

Among enzymes that have been shown to produce tofu are papain, and alkaline and neutral proteases from microorganisms. Papain, moreover, has been studied as a gelling agent to produce "instant tofu" from soy protein isolate and soy glycinin (11S) protein.^[46]^[47]

Contemporary tofu manufacturers may choose to use one or more of these coagulants since each plays a role in producing the desired texture in the finished tofu.^[41] Different textures result from different pore sizes and other microscopic features in the tofu produced using each coagulant. The coagulant mixture is dissolved in water, and the solution is then stirred into boiled soy milk until the mixture curdles into a soft gel.^[38]

Coagulants are typically added at concentrations between 1.5 and 5.0 g/kg. In all coagulants consisting of calcium or magnesium salts, the positive double-bonded ions of the calcium or magnesium are responsible for the coagulation of the soy proteins which become part of the tofu, thereby enhancing its nutritional value. Only 1 part per 1000 of the tofu eaten is coagulant; most of the coagulant reacts with soy protein and is broken down into ions. The non-reactive portion dissolves in the whey and is discarded.^[48]

The curds are processed differently depending on the form of tofu that is being manufactured. For soft silken tofu (嫩豆腐; nèndòufu in Chinese or 絹漉し豆腐 kinugoshi-dōfu in Japanese) or tofu pudding (豆花, dòuhuā OR 豆腐花, dòufuhuā in Chinese or おぼろ豆腐 Oboro-dōfu in Japanese) the soy milk is curdled directly in the tofu's final packaging. For standard firm East Asian tofu, the soy curd is cut and strained of excess liquid using cheesecloth or muslin and then lightly pressed to produce a soft cake. Firmer tofus, such as East Asian dry tofu (豆干' in Chinese or 凍み豆腐 Shimi-dōfu in Japanese) or Western types of tofu, are further pressed to remove even more liquid. In Vietnam, the curd is strained and molded in a square mold, and the end product is called đậu khuôn (molded bean) or đậu phụ (one of the Vietnamese ways to pronounce the Chinese dòufu). The tofu curds are allowed to cool and become firm. The finished tofu can then be cut into pieces, flavored or further processed.^{[citation needed]}

Although tartness is sometimes desired in dessert tofu, the acid used in flavoring is usually not the primary coagulant, since concentrations sufficiently high to induce coagulation negatively affect the flavor or texture of the resulting tofu. A sour taste in tofu and a slight cloudiness in its storing liquid is also usually an indication of bacterial growth and, hence, spoilage.

Color

The whiteness of tofu is ultimately determined by the soybean variety, soybean protein composition, and degree of aggregation of the tofu gel network. The yellowish-beige color of soybeans is due to the color compounds including anthocyanin, isoflavones, and polyphenol compounds; therefore the soybean variety used will predicate the color of the final tofu product.^[49] Ways to reduce the yellow color include reducing isoflavone content by changing the pH of the soy milk solution used in the production of the tofu so that the relevant compounds precipitate out and are removed during the extraction of okara.^[50] The opacity of tofu gel and the off-white color typical of standard uncooked firm tofu is due to the scattering of light by the colloidal particles of the tofu. The addition of higher levels of calcium salts or a high protein content will contribute to forming a denser and more aggregated gel network which disperses more light, resulting in tofu with a whiter appearance.^[51]

Flavor

Tofu flavor is generally described as bland, which is the taste desired by customers in North America. A more beany flavor is preferred in East Asia. The beany or bland taste is generated during the grinding and cooking process, and either a "hot grind" or a "cold grind" can be used to influence the taste. The hot grind method reduces the beany flavor by inactivating the lipoxygenase enzyme in the soy protein that is known to generate off flavors. Eliminating these flavors makes tofu that is "bland". If a cold grind is used lipoxygenase remains and produces the aldehyde, alcohol, and ester volatile compounds that create beany notes.^[48]

Varieties

A wide variety of types and flavors of tofu is available in both Western and Eastern markets. Despite the range of options, tofu products can be split into two main categories: 'fresh tofu', which is produced directly from soy milk, and 'processed tofu', which is produced from fresh tofu. Tofu production also creates important by-products that are used in various cuisines.

Unpressed fresh

Unpressed fresh tofu is gelled soy milk with curd that has not been cut and pressed of its liquid. Depending on whether the soy milk is gelled with bittern (magnesium chloride) solution or a suspension of gypsum (calcium sulphate), different types of unpressed tofu are produced. Gypsum-gelled soft tofu has a smooth and gel-like texture and is commonly known as soft tofu, silken-tofu, or douhua (豆花). The bittern-gelled variety has a very soft spongy curdled texture and is known as extra-soft or sun-dubu (순두부).

Unpressed tofu is so soft that it is directly ladled out for serving or sold with its gelling container.

Extra soft

Sun-dubu (extra soft tofu)

Unpressed bittern-gelled soft tofu is called sun-dubu (순두부; "mild tofu") in Korean. Soy milk is mixed with seawater,^[52]^[53]^[54]^[55]^[56] or saline water made with sea salt, so that it curdles.^[57]^[58] The curds remain loose and soft. Freshly made sun-dubu is eaten boiled with little or no seasoning. Manufactured sundubu is usually sold in tubes. It is also the main ingredient in sundubu-jjigae (순두부찌개; "soft tofu stew").

Although the word sun in sun-dubu does not have a Sino-Korean origin,^[59] sun-dubu is often translated into Chinese and Japanese using the Chinese character 純, whose Korean pronunciation is sun and the meaning is "pure". Thus in China, sun-dubu is called chún dòufu (純豆腐; "pure tofu"), and in Japan, it is called jun-tōfu (純豆腐) or sundubu (スンドゥブ).

Soft

Soft tofu

Soft tofu, also known as "silken tofu", is called nèndòufu (嫩豆腐; "soft tofu") or huádòufu (滑豆腐, "smooth tofu") in Chinese; kinugoshi-dōfu (絹漉し豆腐; "silk-filtered tofu") in Japanese; and yeon-dubu (Korean: 연두부; Hanja: 軟豆腐; "soft tofu") in Korean. Gelled with gypsum, this tofu is undrained, and unpressed, and contains a high moisture content.^[48] Silken tofu is produced by coagulating soy milk without cutting the curd.^[60]^[61] Silken tofu is available in several consistencies, including soft and firm, but all silken tofu is more delicate than regular firm tofu (pressed tofu) and it has different culinary uses.^[62] Silken tofu can be used as a substitute for dairy products and eggs, especially for smoothies and baked desserts.^[63]

Douhua (豆花, also known as 豆腐花, dòufuhuā in Chinese), or tofu brain (豆腐腦 or 豆腐脑, dòufunǎo in Chinese) or dau fa (Cantonese) and tau hua (Fujianese) (豆花; "bean flower") is similar to silken tofu, but is typically served a few hours after it is prepared. It is most often eaten as a hot dessert, but sometimes salty pickles or hot sauce are added. This is a type of soft tofu with very high moisture content. Because using chopsticks make douhua difficult to pick up, it is generally eaten with a spoon. With the addition of flavorings such as finely chopped spring onions, dried shrimp, soy sauce, or chilli sauce, douhua is a popular breakfast dish across China. In Malaysia, douhua is usually served warm with white or dark palm sugar syrup, or served cold with longans. It is frequently served at breakfast or for dessert. It is usually served either with a sweet ginger syrup, or a mushroom gravy called da lu (打卤). It's normally coagulated at the restaurant into a serving container. Douhua is not always considered a type of tofu, but rather a type of food in its own right.

Some variation exists among soft tofus. Black douhua (黑豆花, hēidòuhuā) is a type of silken tofu made from black soybeans, which is usually made into dòuhuā (豆花) rather than firm or dry tofu. The texture of black bean tofu is slightly more gelatinous than regular douhua and the color is greyish in tone. This type of tofu is eaten for its earthy "black bean taste". Edamame tofu is a Japanese variety of kinugoshi tōfu made from edamame (fresh green soybeans); it is pale green in color and often studded with whole edamame.

Pressed fresh

Depending on the amount of water that is extracted from the cut and pressed curds two types of tofu are produced: firm, and extra firm. Fresh tofu is usually sold completely immersed in water to maintain its moisture content and freshness, and to suppress bacterial growth.

Firm

Firm tofu

Firm tofu (called 老豆腐 lǎodòufu in Chinese; 木綿豆腐, momen-dōfu in Japanese, "cotton tofu"; 모두부, mo-dubu in Korean): Although drained and pressed, this form of fresh tofu retains a high moisture content. It has the firmness of raw meat and bounces back readily when pressed. The texture of the inside of the tofu is similar to that of a firm custard. The skin of this form of tofu retains the pattern of the muslin used to drain it, and the outside is slightly more resistant to damage than the inside. It can be picked up easily with chopsticks.^[21]^[48]

A very firm type of momen-dōfu is eaten in parts of Japan, called ishi-dōfu (石豆腐, "stone tofu") in parts of Ishikawa, or iwa-dōfu (岩豆腐, "rock tofu") in Gokayama in the Toyama Prefecture and in Iya in the prefecture of Tokushima. These types of firm tofu are produced with seawater instead of nigari (magnesium chloride), or using concentrated soy milk. Some of them are squeezed using heavy weights to eliminate excess moisture. These products are produced in areas where traveling is inconvenient, such as remote islands, mountain villages, and heavy snowfall areas.

Extra-firm

Dòugān (extra firm tofu)

Dòugān (豆干, literally "dry tofu" in Chinese) or su ji (素鸡, vegetarian chicken) is an extra firm variety of tofu where a large proportion of the liquid has been pressed out. Dòugān contains the least moisture of all fresh tofu, the firmness of fully cooked meat, and a somewhat rubbery feel similar to that of paneer. When sliced thinly this tofu can be crumbled easily. The skin of this form of tofu has the pattern of the muslin used to drain and press it. Western firm tofu is milled and reformed after pressing.

Su ji is a more common type of unflavored, extra-firm tofu. It cannot be crumbled and has a more rubbery texture. One variety of dried tofu is pressed especially flat and sliced into long strings with a cross-section smaller than 2 mm × 2 mm. Shredded dried tofu (豆干絲, dòugānsī in Chinese, or simply 干絲, gānsī), which looks like loose cooked noodles, can be served cold, stir-fried, or added to soup, as with Japanese aburaage.^[21]^[64]

Processed tofu

Many forms of processed tofu exist. Some processing techniques probably ^{[citation needed]} originate before the days of refrigeration from the need to preserve tofu or to increase its shelf life. Other production techniques are employed to create tofus with different textures and flavors.^[65]

Fermented

Pickled tofu

Pickled tofu (豆腐乳 in Chinese, pinyin: dòufurǔ, or 腐乳 fŭrŭ; chao in Vietnamese), also called "preserved tofu" or "fermented tofu", consists of cubes of dried tofu that have been allowed to fully air-dry under hay and slowly ferment with the help of aerial bacteria.^[65] The dry fermented tofu is then soaked in salt water, Chinese rice wine, vinegar or minced chiles, or in a mixture of whole rice, bean paste, and soybeans. In the case of red pickled tofu (紅豆腐乳 in Chinese, Pinyin: hóng dòufurǔ), red yeast rice (cultivated with Monascus purpureus) is added for color.^[a] In Japan, pickled tofu with miso paste is called tofu no misodzuke, and is a traditional preserved food in Kumamoto. In Okinawa, pickled and fermented tofu is called tofuyo (豆腐餻). It is made from Shima-doufu (an Okinawan variety of large and firm tofu). It is fermented and matured with koji mold, red koji mold, and awamori.
Stinky tofu (臭豆腐 in Chinese, Pinyin: chòudòufu) is soft tofu that has been fermented in a vegetable and fish brine.^[65] The blocks of tofu have a pungent cheese smell, sometimes resembling rotting food. Despite its strong odor, the flavor and texture of stinky tofu is appreciated by aficionados, who describe it as delightful. The texture of this tofu is similar to the soft East Asian tofu from which it is made. The rind that stinky tofu develops when fried is said to be best when especially crisp, and fried stinky tofu is usually served with soy sauce, sweet sauce, or hot sauce.^{[citation needed]}

Frozen

Thawed and sliced frozen tofu

Koya-dofu after soaking in water

Thousand-layer tofu (千葉豆腐, qiānyè dòufu, literally "thousand-layer tofu", or 凍豆腐 dòngdòufu, 冰豆腐 bīngdòufu in Chinese, both meaning "frozen tofu") is a frozen tofu. The ice crystals that develop within it result in the formation of large cavities that appear to be layered. Frozen tofu takes on a yellowish hue in the freezing process. Thousand-layer tofu originates from the Jiangnan region of China and is commonly made at home from soft tofu. It is also commercially sold as a specialty in Hong Kong, Taiwan, and other areas with Jiangnan emigrants. It is regularly paired with tatsoi as a winter dish. Frozen tofu is defrosted before serving and sometimes pressed to remove moisture prior to use.

During freezing, the ice crystals puncture cell walls and facilitate the release of free and bound water and cause a decrease in total water content in tofu after freezing then thawing. The initial protein-water bonds are irreversibly replaced by protein-protein bonds, which are more elastic and cause a structural change to the gel network and lead to an increase in textural properties such as hardness, springiness, cohesiveness, and gumminess.^[66]^[67]

In Japan, two kinds of freeze-dried tofu are produced. Those are usually rehydrated by being soaked in water prior to consumption. In their dehydrated state, they do not require refrigeration.

Kori tofu (凍り豆腐, literally "frozen tofu") is freeze-dried.^[68] Koya-dofu (kōya-dōfu, 高野豆腐 in Japanese) is a freeze-dried tofu from Mount Kōya, a center of Japanese Buddhism famed for its shōjin ryōri, or traditional Buddhist vegetarian cuisine. It is said that the method of Koya-dofu was discovered by accident by leaving tofu outdoors in the winter season. It is sold in freeze-dried blocks or cubes in Japanese markets. It is typically simmered in dashi, sake or mirin and soy sauce. In shōjin ryōri, vegetarian kombu dashi, made from seaweed, is used. When prepared in the usual manner, it has a spongy texture and a mildly sweet or savory flavor. The taste and flavor depend on what soup or cooking stock it was simmered in. A similar form of freeze-dried tofu, in smaller pieces, is found in instant soups (such as miso soup), in which the toppings are freeze-dried and stored in sealed pouches.
Shimidofu (凍み豆腐) is mainly consumed in the Tohoku region. While Koya-dofu is made by shade-drying, shimidofu is made by sun-drying.

By-products

Tofu skin

Tofu skin is produced when soy milk is boiled in an open, shallow pan, thus producing a film or skin composed primarily of a soy protein-lipid complex on the liquid surface.^[69] The films are collected and dried into yellowish sheets known as "soy milk skin" (腐皮, fǔpí in Chinese; 湯葉, yuba in Japanese). Its approximate composition is 50–55% protein, 24–26% lipids (fat), 12% carbohydrate, 3% ash, and 9% moisture.^{[citation needed]}

The skin can also be dried into a product known as "tofu bamboo" (腐竹, fǔzhú in Chinese; phù trúc in Vietnamese; kusatake, Japanese), or into many other shapes. Since tofu skin has a soft yet rubbery texture, it can be folded or shaped into different forms and cooked further to imitate meat in vegan cuisine. Some factories dedicate their production to tofu skin and other soy membrane products. Tofu skin is commonly sold in the form of dried leaves or sheets. Other people would put the "tofu bamboo" into congee (a watery rice mixture that is eaten for breakfast) so that the congee becomes more silky and smooth, and gives a whole new texture. Also, soft, fragile skin would be on the congee once it cools down.^{[citation needed]}Tofu skin is cooked with noodles.^[70]

Soy pulp

Okara, from the Japanese 雪花菜(おから) is known as 雪花菜 xuěhuācài, in Chinese, lit. "snowflake vegetable"; 豆腐渣, dòufuzhā, also Chinese, lit. "tofu sediment/residue"; and 콩비지, kongbiji, in Korean).

Sometimes known in the west as "soy pulp" or "tofu lees",^[71] okara is a tofu by-product consisting of the fiber, protein, and starch left over when soy milk has been extracted from ground soaked soybeans.^[72] It is often used as animal feed in most tofu-producing cultures, but also has other uses in Japanese and Korean cuisines, such as in the Korean stew kongbiji jjigae (콩비지찌개). It is also an ingredient for vegetarian burgers in many Western nations. In Japan, it is used to make ice cream.^[73]

Tofu-like foods

The term tofu is used by extension for similarly textured curdled dishes that do not use soy products, such as "almond tofu" (almond jelly), tamago-dōfu [ja] (egg), goma-dōfu [ja] (sesame), or peanut tofu (Chinese 落花生豆腐 luòhuāshēng dòufu and Okinawan jīmāmi-dōfu [ja]).

Due to their East Asian origins and their textures, many food items are called "tofu", even though their production processes are not technically similar. For instance, many sweet almond tofus are actually gelatinous desserts hardened using agar or gelatin. Some foods, such as Burmese tofu, are not coagulated from the "milk" of the legume but rather set in a manner similar to soft polenta, Korean muk, or the jidou liangfen of Yunnan province of southwest China.

Almond tofu

"Almond tofu" (Chinese: 杏仁豆腐 xìngrén dòufu; Japanese: annindōfu) is a milky white and gelatinous substance resembling tofu, but it does not use soy products or soy milk and is hardened with agar. A similar dessert made with coconut milk or mango juices may occasionally be referred to as "coconut tofu" or "mango tofu", although such names are also given to hot dishes that use soy tofu and coconut or mango in the recipe.

Chickpea tofu

Burmese tofu (to hpu in Burmese) is a legume product made from besan (chana dal) flour; the Shan variety uses yellow split pea flour instead. Both types are yellow in color and generally found only in Myanmar, though the Burman variety is also available in some overseas restaurants serving Burmese cuisine.^[74] Burmese tofu may be fried as fritters cut into rectangular or triangular shapes.

A variety called hsan to hpu (or hsan ta hpo in Shan regions) is made from rice flour (called hsan hmont or mont hmont) and is white in color with the same consistency as yellow Burmese tofu when set. It is eaten as a salad in the same manner as yellow tofu.

Egg tofu

Egg tofu [ja] (Japanese: 玉子豆腐, 卵豆腐, tamagodōfu) (Chinese: 蛋豆腐, dàndòufu; often called 日本豆腐, Rìbĕn dòufu, lit. "Japan bean curd") is the main type of savory flavored tofu. Whole beaten eggs are combined with dashi, poured into molds, and cooked in a steamer (cf. chawanmushi). This tofu has a pale golden color that can be attributed to the addition of eggs and, occasionally, food coloring. This tofu has a fuller texture and flavor than silken tofu, due to the presence of egg fat and proteins. Plain "dried tofu" can be flavored by stewing in soy sauce (滷) to make soy-sauce tofu. It is common to see tofu sold from hot food stalls in this soy-sauce stewed form. Today Egg "Japanese" tofu is made of eggs, water, vegetable protein, and seasoning.^[75]

Egg tofu was invented in Japan during the Edo period. The book《万宝料理秘密箱》written in 1785 recorded how to make Japanese tofu. Later the Japanese form of tofu entered Southeast Asia, being introduced to China in 1995 from Malaysia.^[76]^{[citation needed]}

100 grams of Egg tofu has 17 mg calcium, 24 mg magnesium, and 5 grams protein while 100 grams tofu has 138 mg calcium, 63 mg magnesium and 12.2 grams protein. Compared with tofu, Japanese tofu's nutritional value is lower.^{[citation needed]}

Tofu dishes common in Japan include three delicacies (三鲜) Japanese tofu; shrimp Japanese tofu; Japanese tofu in ketchup; teppanyaki Japanese tofu; and Japanese fish-flavored tofu.^{[citation needed]}

Peanut tofu

In Okinawa, Japan, jīmāmi-dōfu [ja] a peanut milk, made by crushing raw peanuts, adding water and straining, is combined with starch (usually sweet potato, known locally as umukuji or umukashi (芋澱粉)) and heated until curdling occurs.

The Chinese equivalent is 落花生豆腐 luòhuāshēng dòufu.

Sesame tofu

The tofu known as goma-dōfu [ja] is made by grinding sesame into a smooth paste, combining it with liquid and kudzu starch, and heating it until curdling occurs. It is often served chilled as hiyayakko.

Preparation

Tofu has very little flavor or smell of its own. Consequently, tofu can be used in both savory and sweet dishes, acting as a bland background for presenting the flavors of the other ingredients used. In order to flavor the tofu it is often marinated in soy sauce, chillis, sesame oil, etc.

In East Asian cooking, tofu is prepared in many ways, including raw, stewed, stir-fried, in soup, cooked in sauce, or stuffed with fillings. The idea of using tofu as a meat substitute is not common in East Asia.