Tofu, sometimes also called doufu (often in Chinese recipes) or bean curd (literal translation), is a food made by coagulating soy milk, and then pressing the resulting curds into blocks. The making of tofu from soy milk is similar to the technique of making cheese from milk. Wheat gluten, or seitan, in its steamed and fried forms, is often mistakenly called “tofu” in Asian or vegetarian dishes.
Tofu is made by coagulating soy milk and pressing the resulting curds. Although pre-made soy milk may be used, most tofu producers begin with their own soy milk, which is produced by soaking, grinding, boiling, and straining dried (or, more rarely, fresh) soybeans.
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. Two types of coagulants (salts and acids) are used commercially. The third type of coagulant, enzymes, is not yet used commercially but shows potential for producing both firm and “silken” tofu:
- Calcium sulfate (gypsum) : 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 has no perceivable taste. Use of this coagulant also makes a tofu that is rich in calcium, an important mineral for treating and preventing osteoporosis. As such, many tofu manufacturers choose to use this coagulant to be able to market their tofu as a good source of calcium.
- Magnesium chloride and Calcium chloride: The coagulant used to make Japanese style tofu with 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 may also contain small quantities of magnesium sulfate (epsom), 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.
- Glucono delta-lactone (GDL): A naturally occurring organic acid also used in cheese making, which produces a very fine textured tofu that is almost jelly-like. This coagulant is used especially for “silken” and softer tofus, and confers a very slightly sour taste to the finished product.
- Among enzymes that have been shown to produce tofu are papain, and alkaline and neutral proteinases from microorganisms. In the case of papain, the enzyme to substrate ratio, by weight, was held constant at 1:400. An aliquot of 1% crude papain was added to “uncooked” soy milk at room temperature and heated to 90–100 celsius .
Contemporary tofu manufacturers may choose to use one or more of these coagulants, since they each play a role in producing a desired texture in the finished tofu. Different textures result from different pore sizes and other microsopic features in tofus produced using each coagulant. The coagulant mixture is dissolved into water, and the solution is then stirred into boiled soy milk until the mixture curdles into a soft gel.
The curds are processed differently depending on the form of tofu that is being manufactured. For soft silken tofu or tofu flower the soy milk is curdled directly in the tofu's selling package. For standard firm Asian tofu, the soy curd is cut and strained of excess liquid using cheese cloth or muslin and then lightly pressed to produce a soft cake. Firmer tofus, such as Asian dry tofu or Western types of tofu, are further pressed to remove even more liquid. The tofu curds are allowed to cool and become firm. The finished tofu can then be cut into pieces, flavoured or further processed.
Although tartness is sometimes desired in dessert tofu, the acid used in flavouring is usually not the primary coagulant since it is not desirable to the flavour or texture of the resulting tofu to add it in a sufficiently high concentration as to induce coagulation. A sour taste in tofu and a slight cloudiness in its storing liquid is also usually an indication of bacterial growth and, hence, spoilage.
There is a wide variety of tofu available in the both western and eastern markets. Despite the daunting variety, 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 side products which are often used in various cuisines.
Depending on the amount of water that is extracted from the tofu curds, fresh tofu can be divided into three main varieties.
- Soft/silken tofu or , nèn doùfu or huá doùfu, in Chinese, lit. “soft tofu” or “smooth tofu”; kinugoshi tofu in Japanese, lit. silk-filtered tofu): This undrained tofu contains the highest moisture content of all fresh tofus Its texture can be described as similar to that of very fine custard. Tofu flower , doù hua or, doùfu hua in Chinese), or tofu brain, doùfu nao in Chinese), often eaten as a dessert, is another type of soft tofu with an even higher moisture content. Because it is nearly impossible to pick up this type of tofu with chopsticks, it is generally eaten with a spoon.
- Asian firm tofu: Although drained and pressed, this form of fresh tofu still contains a great amount of moisture. It has the firmness of raw meat but 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 has the pattern of the muslin used to drain it and is slightly more resilient to damage than its inside. Can be picked up easily with chopsticks.
- Western firm/dried tofu: An extra firm variety of tofu with the least amount of moisture of all fresh tofus. Has the firmness of fully cooked meat and a somewhat rubbery feel. 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 tofu firm tofu is milled and reformed after the pressing and sometimes lacks the skin with its cloth patterning. One variety of dried tofu pressed especially flat and is sliced into long strings with a cross section smaller than 2 mm × 2 mm. This shredded dried tofu is usually served cold like noodles, similar to Japanese aburage.
Fresh tofu is usually sold completely immersed in water to maintain its moisture content.
Many forms of processed tofus exist, due to the varied ways in which fresh tofu can be used. Some of these techniques likely originate from the need to preserve tofu before the days of refrigeration, or to increase its shelf life and longevity. Other production techniques are employed to create tofus with unique textures and flavours
- Pickled tofu: Cubes of dried tofu that have been allowed to fully air-dry under hay and slowly ferment from aerial bacteria. The dry fermented tofu is then soaked in salt water, Chinese wine, vinegar, and minced chiles, or a unique mixture of whole rice, bean paste, and soybeans. In the case of red pickled tofu, pulverized red dates (jujube) or fermented red rice are added for color. Pickled tofu has a special mouth feel similar to certain dairy products due to the breakdown of its proteins which takes place during the air drying and fermentation. Since it does not have a strong odor by itself, pickled tofu takes on the smells and taste of its soaking liquid. The texture of pickled tofu resembles a firm, smooth paste not unlike cold cream cheese. (Indeed, this kind of tofu is sometimes called “Chinese cheese” in English). Pickled tofu is generally sold in small glass jars. When refrigerated, it can keep for several years, during which time its flavor is believed to improve.
- Stinky tofu: A soft tofu that has been fermented in a unique vegetable and fish brine. The blocks of tofu smell strongly of certain pungent cheeses, and are described by many as rotten and fecal. Despite its strong odour, the flavour and mouth-feel of stinky tofu is appreciated by aficionados, who describe it as delightful. The texture of this tofu is similar to the soft Asian tofu that it is made from. The rind that stinky tofu develops from frying is said to be especially crisp, and is usually served with soy sauce and hot sauce.
Almond “tofu”, which is not made of soymilk but rather from gelatin or agaroseFlavourants can be mixed directly into curdling soy milk while the tofu is being produced.
- Sweet: Common sweet dessert tofus include peanut tofu, almond tofu, mango tofu, and coconut tofu. In order to produce these forms of tofu, sugar, fruit acids, and flavourants are mixed into soy milk prior to curdling. Most sweet tofus have the texture of silken tofu and are served cold.
- Products called “almond tofu” in some cases are actually not made from tofu but are instead gelatinous desserts made from agar or gelatin and whitened with milk or coconut milk. In Japan these are canned with syrup and sold as a sweet dessert.
- Savory: Egg tofu is the main type of savory flavoured tofu. Whole beaten eggs are filtered and incorporated into the soy milk before the coagulant is added. The mixture is filled into tube shaped plastic bags and allowed to curdle. The tofu is then cooked in its packaging and sold. Egg tofu has a pale golden colour that can be attibuted to the addition of egg and, occasionally, food colouring. This tofu has a fuller texture and flavour then silken tofu, which can be attributed to the presence of egg fat and protein.
- With the exception of the softest tofus, all forms of tofu can be fried. Thin and soft varieties of tofu are deep fried in oil until they are light and airy in their core.
- Tofus such as firm Asian and dry tofu, with their lower moisture content, are cut into bite-sized cubes or triangles and deep fried until they develop a golden-brown, crispy surface. These may be eaten by themselves or with a light sauce, or further cooked in liquids; they are also added to hot pot dishes or included as part of the vegetarian dish called lo han jai.
- Thousand layer tofu: By freezing tofu, the large ice crystals that develop within the tofu results in the formation of large cavities that appear to be layered. The frozen tofu takes on a yellowish hue in the freezing process. Thousand layer tofu is commonly made at home from Asian soft tofu though it is also commercially sold as a regional specialty in parts of Taiwan . This tofu is defrosted and squeezed of moisture prior to use.
- Japanese freeze-dried tofu: The name comes from Mount Koya , a center of Japanese Buddhism famed for its shojin ryori, or traditional Buddhist vegetarian cuisine. It is excellent for camping, in that it is very light, may be sold flattened, and makes a very filling nutritious meal on the road. Like many freeze-dried foods, it is soaked in hot water or broth before eating, taking on a spongy texture when reconstituted. Freeze-dried tofu is also found in instant soups (such as miso soup), in which the toppings are freeze-dried and stored in sealed pouches.
Byproducts of tofu production
Tofu production creates some edible byproducts. Food products are made from the protein-oil film, or “skin”, that forms over the surface of boiling soy milk in an open shallow pan. The leftover solids from pressing soy milk is called okara.
Tofu skin (yuba)
During the boiling of soy milk, in an open shallow pan , a film or skin composed primarily of a soy protein-lipid complex forms on the liquid surface. The films are collected and dried into yellowish sheets known as tofu skin or soy milk skin. Its approximate composition is : 50–55% protein, 24–26% lipids (fat), 12% carbohydrate, 3% ash, and 9% moisture.
The tofu skin can also be bunched up to stick form and dried into something known as “tofu bamboo”, or a myriad of other forms. Since tofu skin has a rubbery texture, it is folded or shaped into different forms and cooked further to imitate meat in vegetarian cuisine.
Some factories dedicate production to tofu skin and other soy membrane products.
Okara, sometimes known in the west as soy pulp, is the fibre, protein, and starch left over when soy milk has been extracted from ground soaked soybeans. Although it is mainly used as animal feed in most tofu producing cultures, it is sometimes used in Japanese and Korean cuisines. It is also an ingredient for vegetarian burgers produced in many western nations. Okara is rarely seen or used in Chinese cuisine.
Tofu made from other legumes
- Black bean tofu: A type of tofu made from black beans and soybeans, which is usually made into tofu flower rather than firm or dry tofu. The texture of black bean tofu is slighty more gelatinous than regular tofu flower and the colour is greyish in tone. This type of tofu is eaten for the earthy “black bean taste”.
- Burmese tofu: A type of tofu made from chick pea (chana dal) flour instead of soybeans. Originating with the Shan ethnic group, the product is yellow in color and is generally found only in Myanmar , though it is also available in some overseas restaurants serving Burmese cuisine. Burmese Tofu Recipe
Tofu has very little flavour or smell on its own. As such, tofu can be prepared either in savoury or sweet dishes, acting as a canvas for presenting the flavours of the other ingredients used.
Generally, the firmer styles of tofu is used for kebabs, mock meats, and dishes requiring a consistency that holds together, while the softer style can be used for desserts, soups, shakes, and sauces.
Firm western tofus can be barbecued since they will hold together on a barbecue grill. These types of tofu are usually marinated overnight as the marinade does not easily penetrate the entire block of tofu. Grated firm western tofu is sometimes used in conjuction with TVP as a meat substitute. Softer tofus are sometimes used as a dairy free or low calorie filler.
The versatility of tofu and soy protein can be industrially processed to match the textures and flavoured to the likes of cheese, pudding, eggs, bacon, etc. Tofu's texture can also be altered by freezing, pureeing, and cooking. In the Americas , Europe , Australia and New Zealand , tofu is frequently associated with vegetarianism and veganism as it is a source of high quality non-animal protein.
In Asian cooking, tofu is eaten in a myriad of ways, including raw, stewed, stir-fried, in soup, cooked in sauce, or stuffed with fillings. The light greenish “bean” smell of tofu is much enjoyed in East Asian cuisines and fresh tofu is often eaten plain or simply flavoured. In Japan , a common lunch in the summer months is hiyayakko, silken or firm Asian tofu served with freshly grated ginger, scallions, and soy sauce. In many parts of China , fresh tofu is similarly
eaten with soy sauce or further flavoured with katsuobushi shavings, century eggs , and sesame seed oil. A rather famous hot Sichuan preparation using firm Asian tofu is mápó dòufu; in the Shanghai region it is called málà dòufu. In Taiwan , dòuhua is served with toppings like boiled peanuts, azuki beans, cooked oatmeal, tapioca, mung beans and a syrup flavored with ginger or almond. During the summer, dòuhua is served with crushed ice; in the winter, it is served warm. Dòuhua, is a soft tofu dish. The fresh tofu is served warm and here dressed with sweet syrup. A common cooking technique in many parts of East and Southeast Asia involves deep frying tofu in vegetable oil, sunflower oil and canola oil to varied results. Depending on the type of tofu used, the texture of deep fried tofu may range from crispy on the outside and custardy on the inside, to puffed up like a plain doughnut. The former is usually eaten plain in Chinese cuisine with garlic soy sauce, while the latter is either stuffed with fish paste or cooked in soups. In Japan , cubes of lightly coated and fried tofu topped with a kombu dashi-based sauce are called agedashi-dofu. Soft tofu that has been thinly sliced and deep fried, known as aburage in Japan , is commonly blanched, seasoned with soy sauce and mirin and served in dishes such as kitsune udon. Aburage is sometimes also cut open to form a pocket and stuffed with sushi rice; this dish is called inarizushi.
Soft tofu can can also be broken up or mashed and mixed with raw ingredients prior to being cooked. For example, Japanese ganmodoki is a mixture of chopped vegetables and mashed tofu. The mixture is bound together with starch and deep fried. Chinese families sometimes make a steamed meatloaf or meatball dish from equal parts of coarsely mashed tofu and ground pork. In India , tofu is also used as a low fat replacement for paneer providing the same texture with similar taste.
Dried tofu is usually not eaten raw but first stewed in a mixture of soy sauce and spices. Depending on the seasoning used in this cooking method, the tofu may either be called “five spice tofu” or “soy sauce stewed tofu”. It is served thinly sliced with chopped green onions. Most dried tofu is sold after it has been fried or pre-stewed by tofu vendors.
Pickled tofu is commonly used in small amounts together with its soaking liquid to flavour stir-fried or braised vegetable dishes (particularly leafy green vegetables like water spinach). It is often eaten directly as a condiment with rice or congee.
Tofu bamboos are often used in lamb stew or in a dessert soup. Tofu skins are often used as wrappers in dim sum. Freeze-dried tofu and frozen tofu is rehydrated enjoyed in savoury soups. These products are often taken along on camping trips since a small bag of these dried tofu can provide protein for many days.
In Korean cuisine, soft tofu (sundubu in Korean) is used to make a thick soup called sundubu jjigae. Dubu jorim consists of cubes of firm tofu that are pan fried and seasoned with soy sauce, garlic, and other ingredients. Cubes of cold, uncooked tofu seasoned with soy sauce, scallions, and ginger, prepared in a manner similar to the Japanese hiyayakko (described earlier) are also enjoyed.
Very little is known about the exact historic origins of tofu and its method of production. While there are many theories regarding tofu's origins, historical information is scarce enough as to relegate the status of most theories to either speculation or legend. Like the origins of cheese and butter, the exact origin of tofu production may never be known or proven.
What is known is that tofu production is an ancient technique. Tofu was widely consumed in ancient China , and techniques for its production and preparation were eventually spread to many other parts of Asia .
Three theories of origin
The most commonly held of the three theories of tofu's origin maintains that tofu was invented in Northern China around 164 BC by Lord Liu An, a prince during the Han Dynasty. Although this is possible, the paucity of concrete information about this period makes it difficult to conclusively determine whether or not Liu An invented the method for making tofu. Furthermore, in Chinese history, important inventions were often attributed to important leaders and figures of the time.
Another theory states 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 likely have contained calcium and magnesium salts, allowing the soy mixture to curdle and produce a tofu-like gel.1 This may have possibly been the way that tofu was discovered, since soy milk has been eaten as a savory soup in ancient as well as modern times. Despite its technical plausibility, there is little evidence to prove or disprove that tofu production originated in this way.
The last group of theories maintains that the ancient Chinese learned the method for the curdling of soy milk by emulating the milk curdling techniques of the Mongolians or East Indians. For, despite their advancement, no technology or knowledge of culturing and processing milk products existed within ancient Chinese society. The primary evidence for this theory lies with the etymological similarity between the Chinese term for Mongolian fermented milk (rufu, which literally means “milk spoiled”) and the term doufu or tofu. Although intriguing and possible, there is no evidence to substantiate this theory beyond the point of academic speculation.
Established history of tofu
Although its development likely preceded Liu An, tofu is known to have been a commonly produced and consumed food item in China by the 2nd century BC. Although the varieties of tofu produced in ancient times may not have been identical to those of today, descriptions from writings and poetry of the Song and Yuan Dynasty show that the production technique for tofu had already been standardized by then, to the extent that they would be similar to tofu of contemporary times.
Tofu and its production technique were subsequently introduced into Japan in the Nara period (late eighth century) as well as other parts of East Asia . This spread likely coincided with the spread of Buddhism as it is an important source of proteins in the religion's vegetarian diet. Since then, tofu has become a staple in many countries, including Vietnam , Thailand , and Korea , with subtle regional variations in production methods, texture, flavour, and usage.
Tofu was not well known to most Westerners before the middle of the 20th century. However, with increased cultural contact and an interest in vegetarianism, tofu has become a more familiar product to Westerners.
Nutrition and health information
Tofu is low in calories, contains beneficial amounts of iron (especially important for women of child bearing age) and has no cholesterol (a risk factor for heart disease). Depending on the coagulant used in manufacturing, the tofu may also be high in calcium (important for bone development and maintanence) and magnesium (especially important for athletes).
Tofu is relatively high in protein, about 10.7% for firm tofu and 5.3% for soft “silken” tofu with about 2% and 1% fat respectively as a percentage of weight.3
In 1995, the New England Journal of Medicine published a report2 that concluded that soy protein is correlated with significant decreases in serum cholesterol, low density lipoprotein (LDL; “bad” cholesterol) and triglyceride concentrations. However, high density lipoprotein (HDL; “good” cholesterol) did not increase. Soy phytoestrogens (isoflavones: genistein and daidzein) adsorbed onto the soy protein were suggested as the agent reducing serum cholesterol levels. On the basis of this research PTI, in 1998, filed a petition with the FDA for a health claim that soy protein may reduce cholesterol and the risk of heart disease.
The FDA granted this health claim for soy: “25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.” One serving (1 cup or 240 ml) of soy milk, for instance, contains 6 or 7 grams of soy protein.
In January 2006 an American Heart Association review (in the journal Circulation) of a decade long study of soy protein benefits casts doubt on the FDA allowed “Heart Healthy” claim for soy protein. The panel also found that soy isoflavones do not reduce post menopause “hot flashes” in women nor do isoflavones help prevent cancers of the breast, uterus, or prostate.
Sales and distribution
In the West, tofu can be obtained in Asian markets, farmers' markets, and health food stores. Depending on its local popularity, many grocery stores also stock tofu. The largest provider of tofu products in the United States is Hong Kong-based Vitasoy, which also manufactures the brands Nasoya and Azumaya. Another major brand is Mori-Nu (Morinaga Nutritional Foods), a subsidiary of Morinaga Milk Company of Japan , which pioneered the sale of shelf-stable, aseptically packaged tofu.
In the East, tofu may be produced locally by relatively small vendors or distributed widely by large national brands. Fresh tofu is usually bought from local vendors and is sold directly from large bins or pots at open air markets. Asian firm tofu and “tofu flower” are commonly sold in this manner and are usually no more than a few hours old. Tofu that is sold by large manufacturers often comes packaged in sealed plastic cartons or tubes, and may be at most two weeks old. Most silken and flavoured tofus are produced by large factories. This is due to the fact that such factories have the facilities to meet the required sanitary conditions for production of these forms of tofu on a large scale. In Chinese supermarkets, tofu can be found in many different flavours and grades of consistency.
The English word “tofu” comes from the Japanese tofu, which itself derives from the Chinese dòufu . Although in both languages the characters together translate as “bean curd”, the literal meaning of the individual characters is “bean” and “rotten”.
Unless one purchases it in sterilized containers, tofu does require some choosing when purchasing and some care while storing:
- Tofu can be easily spoiled if not refrigerated properly during transportation; any trace of sour odour or taste is a tell-tale sign of staleness or spoilage.
- Smaller supermarkets may sell sour tofu because some do not use refrigerated trucks for delivery.
- Once purchased, unpackaged tofu should be kept in the refrigerator. The water in which the tofu is kept should be changed on a daily basis and the tofu should be consumed or cooked within several days. Tofu in sealed packages can be kept from one to several weeks in the refrigerator. Tofu packaged in aseptic Tetra Brik containers has a shelf life of one year if unopened.
- Tofu is so highly esteemed in Korean culture that the menus of many Korean restaurants are based almost entirely on tofu, including some which feature only tofu and red chili paste soup.
- The book Tofu Hyakuchin, published in the Edo period, lists 100 recipes for cooking tofu.
- In Chinese, the term “to eat tofu” is a commonly used euphemism for implying the unsolicited groping of a woman's breast or other body parts.
- Also in Cantonese Chinese language, the term “mash tofu” is slang term for calling lesbian sex.
- In Chinese culture, 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, and that only tofu is soft enough for them to eat.
- Buddhist monks use tofu as a substitute for meat, since tofu can be made to resemble the texture of meat if cooked properly. In Chinese cuisine there are numerous tofu dishes cooked to imitate the texture and flavours of meat.
- In the popular Japanese boy racer anime Initial D, the lead character, Takumi (a late night tofu delivery driver) learns, over a period of years, how to drive very fast in his car on a winding mountainous road without spoiling and destroying his father's freshly-made tofu.
- There is a popular Japanese girl group called the Tofoos; its members include Stefoo and Queenfoo