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Tofu, also , doufu or bean curd , is a food of origin, made by soy milk, and then pressing the resulting curds into blocks. There are many different varieties of tofu, including fresh tofu and tofu that has been processed in some way. Tofu has very little flavor or smell on its own, so it can be used either in savory or sweet dishes, and is often seasoned or marinated to suit the dish.
The production of tofu from soy milk is similar to the production of cheese from milk, although some tofu is made by processing non-soy products, such as almonds or black beans. The byproduct of the process is .
Tofu originated in ancient China, The third type of coagulant, enzymes, is not yet used commercially but shows potential for producing both firm and "silken" tofu.
*Calcium sulfate : 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 or Lushui - 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 tofu with a smooth and tender texture. In Japan, a white powder called ''nigari'', which consists primarily of magnesium chloride, is produced from after the sodium chloride is removed and the water evaporated, which is called Lushui in China. Depending on its production method, ''nigari/Lushui'' may also contain small quantities of magnesium sulfate , 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.
*Glucono delta-lactone : 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.
*Among enzymes that have been shown to produce tofu are papain, and alkaline and neutral 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. Its texture can be described as similar to that of very fine custard. In Japan and Korea, traditional soft tofu is made with . ''Douhua'' , or ''tofu brain'' , 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'' ; it is pale green in color and often studded with whole ''edamame''.
* 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.
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 flavors.
*Pickled tofu : 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.
*Stinky tofu : A soft tofu that has been fermented in a unique vegetable and fish brine.
The skin can also be bunched up to stick form and dried into something known as "tofu bamboo" , or myriad 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.
, 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.
:''To hpu'' may be fried as fritters cut in rectangular or triangular shapes; the latter fried twice, hence the name ''hnapyan gyaw'' , 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 or fish crackers.
:Rice tofu, called ''hsan to hpu'' is made from rice flour 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.
Tofu has very little flavor or smell on its own. As such, tofu can be prepared either in savory or sweet dishes, acting as a canvas for presenting the flavors of the other ingredients used.
In Asian cooking, tofu is eaten in myriad 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 flavored.
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 flavored with ''katsuobushi'' shavings, century eggs , and sesame seed oil.
In Chinese cuisine, '''' 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 ''hiyayakko'' are also enjoyed.
In the Philippines, the sweet delicacy taho is made of fresh tofu with brown sugar syrup and sago. The Malaysian version of taho or douhua is called tofufa. Warm soft tofu is served in 'slices' in a bowl with either pandan-flavored sugar syrup or palm sugar syrup.
In Vietnam, ''dòuhuā'' is pronounced ''??u h?''. 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.
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 or cooked in soups. although 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. 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 book ''Tofu Hyakuchin'' , published in the Edo period, lists 100 recipes for cooking tofu.
The rise in acceptance of tofu likely coincided with that of Buddhism as it is an important source of proteins in the religion's vegetarian diet.
In 1995, a report from the University of Kentucky, financed by St. Louis, Missouri , concluded that soy protein is correlated with significant decreases in serum cholesterol, Low Density Lipoprotein LDL and triglyceride concentrations. However, High Density Lipoprotein did not increase. Soy phytoestrogens 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." 100 grams of firm tofu, for instance, contains 11.5 grams of soy protein. In January 2006 an American Heart Association review of a decade-long study of soy protein benefits showed only a minimal decrease in cholesterol levels, but it compared favorably against animal protein sources.
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.
A study done by the Pacific Health Research Institute followed over 3000 Japanese men between 1965 and 1999, which showed a positive correlation between cerebral atrophy and consumption of tofu.
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.