Tofu

Tofu (the Japanese Romaji spelling), also known as doufu (the Chinese Pinyin spelling often used in Chinese recipes) or bean curd (the literal translation), is a food of Chinese origin, 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 (Fermentation). Wheat gluten, or seitan, in its steamed and fried forms, is often called "tofu" in Asian or vegetarian dishes.

Production
Tofu is made by coagulating soy milk and pressing the resulting curds. Although pre-made soy milk may be used, most tofu producers begin by making their own soy milk, which is produced by soaking, grinding, boiling, and straining dried (or, less commonly, 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.

Salt coagulants

 * 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.


 * Chloride-type Nigari salts - Magnesium chloride and calcium chloride: Both of these salts have a high solubility rate 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 for tofu formation.  These are the coagulants used to make Japanese-style 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 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 a common coagulant for tofu in North America.

Acid coagulants

 * 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 an almost imperceptible sour taste to the finished product.  Commonly used together with calcium sulfate to give soft tofu a smooth tender texture.

Enzyme coagulants

 * 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 degrees 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 microscopic 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 (嫩豆腐; nèn dòufǔ) or tofu flower (豆花, dòuhuā) 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 (荳乾) or Western types of tofu, are further pressed to remove even more liquid. In Viet Nam, 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 doufu). 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 so 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.

Varieties
There is a wide variety of tofu available in 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.

Fresh tofu
Depending on the amount of water that is extracted from the tofu curds, fresh tofu can be divided into three main varieties. Fresh tofu is usually sold completely immersed in water to maintain its moisture content.
 * Soft/silken tofu (嫩豆腐 or 滑豆腐, nèn dòufǔ or huá dòufǔ, in Chinese, lit. "soft tofu" or "smooth tofu"; 絹漉し豆腐, kinugoshi tōfu in Japanese, lit. "silk-filtered tofu"; 순두부, sundubu in Korean, lit. "mild 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.  In Japan and Korea, traditional soft tofu is made with seawater.  Douhua (豆花, dòu huā or 豆腐花, dòufǔ  huā in Chinese), or tofu brain (豆腐腦 or 豆腐脑, dòufǔ naǒ in Chinese), often eaten as a dessert, but sometimes with salty pickles or hot sauce added instead, 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.  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.
 * Asian firm tofu (simply called 豆腐 dòufǔ  in Chinese; 木綿豆腐, momendōfu in Japanese, lit. "cotton 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 (豆乾, dòu gān in Chinese, lit. "dry tofu"): An extra firm variety of tofu with the least amount of moisture of all fresh tofus. It has the firmness of fully cooked meat and a somewhat rubbery feel similar to 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 the pressing and sometimes lacks the skin with its cloth patterning.  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 (豆乾絲, dòu gān sī in Chinese, or simply 乾絲, gān sī), which looks like loose cooked noodles, and can be served cold, stir-fried, or similar in style to Japanese aburaage.photo

Processed tofu
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.

Fermented

 * Pickled tofu (豆腐乳 in Chinese, pinyin: dòufǔ rǔ, lit. "tofu dairy," or 腐乳; chao in Vietnamese): Also called "preserved tofu" or "fermented tofu," this food consists of 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 (紅豆腐乳 in Chinese, Pinyin: hóng dòufǔ rǔ), red yeast rice (cultivated with Monascus purpureus) is added for color.
 * Stinky tofu (臭豆腐 in Chinese, Pinyin: chòu dòufǔ): 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 mouthfeel 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, sweet sauce, and/or hot sauce.

Flavoured
Flavours can be mixed directly into curdling soy milk while the tofu is being produced.
 * Sweet: Common sweet dessert tofus include peanut tofu (落花生豆腐, luòhuāshēng dòufǔ in Chinese and jimami-dōfu in Japanese), almond tofu (杏仁豆腐, xìngrén dòufǔ in Chinese; 杏仁豆腐, annindōfu in Japanese), 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.
 * Savoury: Egg tofu (蛋豆腐; dàn dòufǔ, in Chinese) (玉子豆腐; yùzǐ dòufǔ; lit. "jade tofu," in Chinese; 卵豆腐; tamagodōfu, in Japanese) is the main type of savoury 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 color that can be attributed to the addition of egg and, occasionally, food coloring.  This tofu has a fuller texture and flavour than silken tofu, which can be attributed to the presence of egg fat and protein.

Fried

 * 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 (豆泡 in Chinese, dòupào, lit. "bean bubble," describing the shape of the fried tofu as a bubble).
 * 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 (炸豆腐 in Chinese, zhà dòufǔ, lit. "fried tofu"). 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 luohan zhai.

Frozen

 * Thousand layer tofu (千葉豆腐, 凍豆腐 or 冰豆腐 in Chinese, lit. "thousand layer tofu" or "frozen 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 (pseudostratified). 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 sometimes squeezed of moisture prior to use.
 * Japanese freeze-dried tofu (kōyadōfu, 高野豆腐 in Japanese): The name comes from Mount Koya, a center of Japanese Buddhism famed for its shōjin ryōri, 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," which 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
Boiling of soy milk, in an open shallow pan, produces 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, fǔ pí 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 bunched up to stick form and dried into something known as "tofu bamboo" (腐竹, fǔ zhú in Chinese; phù chúc in Vietnamese; kusatake, Japanese), or a myriad of other forms. Since tofu skin has a soft yet 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
Okara (雪花菜, xuě huā caì, lit. "snowflake vegetable"; 豆腐渣, dòufǔ zhā, lit. "tofu sediment/residue"; kongbiji, 콩비지 in Korean), 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.

Tofu made from other legumes and grains



 * Black bean tofu (黑豆花): A type of tofu made from plain black beans and 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 tofu flower and the color is greyish in tone.  This type of tofu is eaten for the earthy "black bean taste."
 * Burmese tofu (to hpu in Burmese): A type of tofu made from besan (chana dal) flour instead of soybeans; 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 recipe


 * To hpu may be fried as fritters cut in rectangular or triangular shapes; the latter fried twice, hence the name hnapyan gyaw (literally "twice fried"), is the common form in the Shan States. To hpu nway, creamy and soft before it sets, is also popular served hot on its own or with rice noodles.  To hpu gyauk, which are deep fried, thin, and crispy, are similar to prawn or fish crackers.


 * Rice tofu, 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.

Preparation
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.

Eastern methods
In Asian cooking, tofu is eaten in myriad ways, including raw, stewed, stir-fried, in soup, cooked in sauce, or stuffed with fillings.

Lightly flavoured
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 (冷奴), 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 (皮蛋), and sesame seed oil.

In Chinese cuisine, Dòuhuā (豆花) 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, dòuhuā is served with crushed ice; in the winter, it is served warm.

In Korean cuisine, 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 hiyayakkoare also enjoyed.

In the Philippines, the sweet delicacy taho is made of fresh tofu with brown sugar syrup and sago.

In Vietnam, dòuhuā is pronounced đậu hủ. This variety of soft tofu is made and carried around in an earthenware jar. It is served by being scooped into a bowl with a very shallow and flat spoon, and eaten with either powdered sugar and lime juice or with a ginger-flavored syrup. It is generally eaten hot, even during summer.

Fried
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. Although tofu is often sold preprocessed into fried items, pre-fried tofu is seldom eaten directly and requires additional cooking. 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 (揚げ出し豆腐). 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 (稲荷寿司).

Soups, stews, and braised dishes
A rather famous hot Sichuan preparation using firm Asian tofu is mápó dòufu (麻婆豆腐). This involves braised tofu in a beef, chili, and a fermented bean paste sauce. In the Shanghai region it is called málà dòufǔ (麻辣豆腐).

Dried tofu is usually not eaten raw but first stewed in a mixture of soy sauce and spices. Some types of dried tofu are preseasoned with special blends of spices, so that the tofu may either be called "five spice tofu" (五香豆腐) or "soy sauce stewed tofu" (鹵水豆腐). Dried tofu is typically served thinly sliced with chopped green onions or with slices of meat for added flavor. Most dried tofu is sold after it has been fried or pre-stewed by tofu vendors.

Soft tofu 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.

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 are rehydrated and 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 (순두부 찌개).

As flavouring
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.

Western methods
Generally, the firmer styles of tofu are used for kebabs, mock meats, and dishes requiring a consistency that holds together, while the softer styles 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 (freezing and thawing prior to marinating will significantly reduce the marinade time required). Grated firm western tofu is sometimes used in conjunction with TVP as a meat substitute. Softer tofus are sometimes used as a dairy-free or low-calorie filler. Silken tofu may be used to replace cheese in certain dishes (such as lasagna).

Tofu and soy protein can be industrially processed to match the textures and flavours 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.

History
Tofu originated in ancient China, however little else 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 Han Dynasty prince. Although this is possible, the paucity of concrete information about this period makes it difficult to conclusively determine whether 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. 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. Its technical plausibility notwithstanding, 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 maintenance), and magnesium (especially important for athletes).

Protein
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.

In 1995, the New England Journal of Medicine (Vol. 333, No. 5) published a report from the University of Kentucky entitled, "Meta-Analysis of the Effects of Soy Protein Intake on Serum Lipids." It was financed by the PTI division of DuPont, The Solae Co. St. Louis, Missouri. This meta-analysis 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) absorbed 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 Food and Drug Administration 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 cast doubt on the FDA allowed "Heart Healthy" claim for soy protein. Among the conclusions the authors state, "In contrast, soy products such as tofu, soy butter, soy nuts, or some soy burgers should be beneficial to cardiovascular and overall health because of their high content of polyunsaturated fats, fiber, vitamins, and minerals and low content of saturated fat. Using these and other soy foods to replace foods high in animal protein that contain saturated fat and cholesterol may confer benefits to cardiovascular health."

Isoflavones
Soy isoflavones have not been shown to reduce post menopause hot flashes in women and the efficacy and safety of isoflavones to help prevent cancers of the breast, uterus or prostate is in question. Thus, soy isoflavone supplements in food or pills is not recommended. The original paper is in the journal Circulation: January 17, 2006.

A study done by the Pacific Health Research Institute followed over 3000 Japanese men between 1965 and 1999, which showed a positive correlation between brain atrophy and consumption of tofu. Nevertheless, this is a single study and by itself, does not show conclusively that soy isoflavones cause brain atrophy.

This study by L.R. White, et al., from the National Institute of Aging, NIH, was rejected as not credible by the Food and Drug Administration when it issued its 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."

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 House Foods America Corp, a subsidiary of Japan based company, House Foods Corp.

House Foods America Corp. has tofu plants in California and New Jersey with a combined capacity of manufacturing 350,000 pieces of tofu per day. Other major brands are Vitasoy, a subsidiary of a Hong Kong based company, which also manufactures the brands Nasoya and Azumaya; and 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 street 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.

Etymology
The English word "tofu" comes from the Japanese tōfu (豆腐),  which itself derives from the Chinese dòufǔ (豆腐 or 荳腐). Although in both languages the characters together translate as "bean curd," the literal meaning of the individual characters is "bean" (豆) and "curdled" (腐).

Choosing tofu
Unless one purchases it in sterilized containers, tofu does require some choosing when purchasing and some care while storing:
 * Tofu can easily be spoiled if not refrigerated properly during transportation; any trace of sour odour or taste is a tell-tale sign of staleness or spoilage.
 * 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 have a shelf life of one year if unopened.

Miscellaneous

 * 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 sundubu jjigae (a stew made with soft tofu and gochujang (red chili paste).
 * The book Tofu Hyakuchin (豆腐百珍), published in the Edo period, lists 100 recipes for cooking tofu.
 * 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.  See Buddhist cuisine.
 * Chinese war hero Guan Yu used to be a tofu maker before he enlisted in the army.
 * Before refrigeration was available in China, tofu was often only sold during the winter time, due to the tofu not spoiling in the colder weather. During the warmer months, any leftover tofu would be spoiled if left for more than a day.
 * Chinese martial arts expert and hero, Yim Wing-chun, was a celebrated tofu maker in her village. Tofu as such plays a part in the 1994 movie about her life, "Wing Chun".