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Tofu

Views:0     Author:Site Editor     Publish Time: 2021-07-09      Origin:Site

Tofu, also known as bean curd, is a food prepared by coagulating soy milk and then pressing the resulting curds into solid white blocks of varying softness; it can be silkensoftfirmextra firm or super firm. Beyond these broad textural categories, there are many varieties of tofu. It has a subtle flavor, so it can be used in savory and sweet dishes. It is often seasoned or marinated to suit the dish and its flavors, and due to its spongy texture it absorbs flavors well. 

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

Tofu originated in China and has been consumed within China for over 2,000 years. It is also a traditional component of the cuisines of Indonesia, Japan, Korea, Vietnam, Singapore, Thailand,  and the Philippines.  In modern Western cooking it is sometimes treated as a meat substitute.

Production

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

  1. The preparation of soy milk

  2. The coagulation of the soy milk to form curds (douhua)

  3. 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. 

Coagulation of the protein and oil (emulsion) suspended in the 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. 

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. As the net charges of the protein molecules are neutralized, attractive hydrophobic interactions dominate over repulsive electrostatic charges, and protein aggregates are formed.

Two types of coagulants (salts and acids) are used commercially. 

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 in whether the soy-milk is gelled with bittern (magnesium chloride) solution or a suspension of gypsum (calcium sulphate), different types of unpressed tofu is 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

Unpressed bittern-gelled soft tofu is called sun-dubu (순두부; "mild tofu") in Korean. Soy milk is mixed with seawater,  or saline water made with sea salt, so that it curdles.  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 doesn't have a Sino-Korean origin,  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, 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 (연두부; 軟豆腐; "soft tofu") in Korean. Gelled with gypsum, this tofu is undrained, unpressed and contains a high moisture content. Silken tofu is produced by coagulating soy milk without cutting the curd.  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. Silken tofu is used as a substitute for dairy products and eggs, especially for smoothies and baked desserts.


Similar to silken, but is typically served a few hours after it is made is 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"). 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 a very high moisture content. Because it is difficult to pick up with chopsticks, 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 (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. 

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 (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 amount of moisture of all fresh tofu and has 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. 

Processed tofu 

Many forms of processed tofu exist. Some processing techniques probably 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. 

Fermented

  • 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. 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. 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 a soft tofu that has been fermented in a vegetable and fish brine. 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. 

Frozen

  • 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 which cause a structural change to the gel network and lead to an increase in textural properties such as hardness, springiness, cohesiveness and gumminess. 

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. 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 dashisake 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 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. 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. 

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 in breakfast) so that the congee becomes more silky and smooth, and gives a whole new texture. Also, a soft, fragile skin would be on the congee once it cools down. 

Soy pulp 

Main article: Okara (food)

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",  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.  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. 

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   (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 

Main article: Burmese 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.  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 (Japanese: 玉脂豆腐, 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. 

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. 

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. 

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. 

Peanut tofu 

In Okinawa, Japan, jīmāmi-dōfu   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  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.


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