Method of manufacturing an instant bean curd or tofu, and the toju made by such method

Beans are soaked and ground to form a mush (go), and the mush is heated and powderized. A thickening agent having a gelatinizing property is mixed with the powder. The tofu is prepared by mixing the powder with water and an additional amount of gelatinizing material.

This invention relates to a method of preparing instant "tofu" (bean curds) 
which enables one to easily prepare tofu merely by adding cold or hot 
water to a powder of "go" material of tofu, without the necessity of 
heating or boiling the mixture. 
Heretofore, various research and development programs have been made to 
provide an instant tofu which enables anyone readily to prepare tofu at 
any time and place, and some products of this nature have been placed on 
the market. In the usual manufacture of tofu, washed soybeans are soaked 
in water, and after having swelled they are ground together with water 
into a mushy material called "go." The go is then heated and separated by 
filtration to produce soybean milk, soluble ingredients, and "okara" (bean 
curds refuse), the okara consisting mainly of insoluble substances. Most 
of the prior art instant tofus referred to above are made from the soybean 
milk prepared as described above or prepared from powdered soybean milk 
(dried soybean milk). In the prior art method, after being mixed and 
heated with an amount of water, for example, the soybean milk is 
coagulated in a vessel with an addition of a coagulant, or the soybean 
milk is mixed in advance with a coagulant and then coagulation is obtained 
by heating and boiling the soybean milk for several minutes and then 
leaving it to cool. These methods require heating means for the 
preparation of tofu and requires several minutes before tofu is obtained. 
Furthermore, the use of soybean milk or powdered soybean milk results, in 
the course of its production, in a large amount of the by-products, okara. 
Despite its residual nutritive ingredients such as proteins, 
carbohydrates, and minerals, the okara has had only limited uses, such as 
livestock feed, and it is consumed very uneconomically from the standpoint 
of the effective use of food resources. However, the simple addition of 
okara in the course of tofu manufacture will result only in a poor taste 
of the tofu with a rough "feel" inevitable, and it may be very difficult 
to obtain a tofu having a substantial and yet smooth feel to the palate 
which is peculiar to tofu. Therefore, the constituents of okara have 
seldom been used in the manufacture of instant tofu. 
It is an object of the present invention to provide a method of 
manufacturing instant tofu, in which the constituents of okara are 
effectively used. 
Another object of this invention is to provide a method of manufacturing 
instant tofu which can be readily prepared by merely adding cold or hot 
water, without necessitating the use of heating means. 
According to the method of this invention, the go made from bean materials 
is heated and then directly dried and powdered without being separated 
into soybean milk and okara, or the go is mixed with an acid or alkali 
earth metal salt and coagulated into curds and then dried and powdered. To 
produce tofu, the powder thus obtained is admixed with a gelatinizing 
agent used as a thickener, and coagulated in a form. 
In accordance with this invention, the go obtained from bean material is 
heated at a temperature of approximately 90.degree. to 100.degree. C. for 
about 1 to 10 minutes, and preferably coagulated into curds by an addition 
of an acid or alkali earth metal salt. The reason for limiting the 
temperature to the range from 90.degree. to 100.degree. C. is that below 
90.degree. C. the detrimental substance in soybeans, such as trypsin 
inhibitor, is not sufficiently inactivated, and the characteristic flavor 
of tofu becomes feeble. Above 100.degree. C., on the other hand, a 
browning in color and a change in odor occur and deteriorate the quality. 
The go used in this invention is made, as mentioned above, from common 
soybeans or defatted soybeans soaked in water (of about 13 to 15 parts to 
1 part of soybeans for one night so that the water content becomes 120% by 
weight of the soybeans) and ground (by a colloid mill, for example, to a 
grain size finer than 50.mu.) and heated. The material for preparing go is 
not limited to soybeans, but one kind or a mixture of several kinds of 
beans may be used, such as peanuts and broad beans or water soluble 
isolated soybean protein may also be used. The heating step is for 
sterilization of various microorganisms, removal of grassy-smell, 
destruction of trypsin inhibitor, and improvement of the coagulating 
property. The heated go is directly transferred to the next powdering 
step, or, perferably, it is converted into curds before powdering it, to 
improve the taste, to facilitate the preparation, and to shorten the time 
required for preparation. As the coagulant for converting the go into 
curds, organic acids such as ardonic acids, uronic acids, citric acid, and 
malic and inorganic acids such as hydrochloric acid are used, and they are 
added in such an amount that the pH value of the go becomes approximately 
3.5 to 5.5. Alkali earth metal salts such as calcium carbonate, calcium 
sulfate, alum, and magnesium sulfate can also be used, and added to the go 
in a quantity of about 0.1 to 10% by weight of the go when 
CaSO.sub.4.2H.sub.2 O is used, and when other salts are used, in a 
quantity equivalent to the CaSO.sub.4.2H.sub.2 O with respect to 
Ca.sup.++. Lactones of ardonic acids and uronic acids such as gluconic 
lactone, arabonic lactone, galactonic lactone, and manonic lactone, which 
produce organic acids by decomposition under the presence of water and 
heat, can also be used. The heated go or curds obtained as described above 
is then powdered by a customary drying process such as freeze-drying. If 
the grain size of the powder is reduced to less than 50.mu., in this case 
the taste and the feel of the tofu to the tongue will be remarkably 
improved with dissolved roughness and increased smoothness to the tongue 
peculiar to tofu. The curds powder is then mixed with a thickening agent 
having a gelatinizing ability and thoroughly stirred. The thickening agent 
such as alginate, pectin, and mannan, preferably by pectin (6% by weight 
of pectin is added to the curds powder) is gelatinized by a gelatinizing 
agent. 
A given amount of the thus obtained mixed powder and water in an amount of 
about 8 to 10 times by weight of the mixed powder, are put into a vessel 
of a given form after manual stirring 20 to 30 times with, for examples, a 
dining fork, thoroughly mixing with a gelatinizing agent in an amount of 
1/10-1/50 by weight of the mixed powder to gelatinize the above thickener. 
When this mixture is allowed to stand for about 3 to 15 minutes, tofu is 
formed. The gelatinizing agents used for gelatinizing the thickening agent 
include alkali earth metal salts such as calcium carbonate, calcium 
sulfate, alum, and magnesium sulfate, and saccharides such as frutose, 
sucrose, and glucose. Preferable gelatinizing agents here are calcium 
carbonate and calcium sulfate; other Ca salts and Mg salts are not 
favorable because they affect the taste of tofu adversely. Saccharides are 
also not favorable because they must be used in such large quantities to 
obtain the expected effect that the result is a too sweet tofu. However, 
if a tofu-like new soybean food having a sweet taste is to be produced, 
such as soybean milk added with sugar or honey for an easy-to-make drink, 
it may be favorable to use saccharides. 
The present invention, as described above, makes it possible to utilize the 
insoluble ingredients (okara ingredients) in go, which has conventionally 
been removed in the process of tofu manufacture and used only as a 
livestock feed, effectively as a constituent of instant tofu which has a 
smooth feel to the tongue identical to the usual tofu. Thus, the invention 
largely contributes to the improvement of nutrition and the elevation of 
productivity, preventing the loss of the nutritious ingredients of beans 
and raising the yield. Further, the invention permits anyone to readily 
prepare tofu at any time and in any place only by admixing cold or hot 
water with the material, and thus it is very useful in respect to 
manufacture, nutrition, and preparation.

EXAMPLE 1 
Five kilograms of defatted soybeans were soaked and swelled in 50 liters of 
hot water at 60.degree. C. for about 1 hour and were finely ground to a 
grain size below 50.mu.. After being heated about 5 minutes at a 
temperature about 95.degree. C., the ground material was spray-dried and 
4.8 kg of powder having a grain size below 50.mu. was obtained. (The grain 
size below 50.mu. is easily attained by controlling the atomizer attached 
to the spray-drier.) Forty grams of this powder, 6 g of low metoxyl 
pectin, and 0.5 g of citric acid were mixed in a molding vessel and mixed 
with an addition of 400 ml of water. Then, it is added to 2.5 g of calcium 
carbonate and thoroughly mixed again. After the mixture was left to stand 
for 10 minutes at room temperature, a piece of tasty tofu, somewhat sticky 
but scarcely rough to the tongue and having a sesame-tofu-like appearance, 
was obtained. 
EXAMPLE 2 
Five kilograms of soybeans were soaked in 40 liters of water overnight, and 
after being ground, they were heated 5 minutes at 95.degree. C. When the 
temperature was dropped to 90.degree. C., it was added to 178 g of glucono 
delta-lactone and thoroughly stirred. After being left standing for about 
2 hours, it was formed into curds. The curds were then freeze-dried and 
ground into 4.5 kg of curds powder. Forty grams of this powder and 3 g of 
sodium alginate were put into a molding vessel and thoroughly mixed with 
an addition of 400 ml of water. Then, the mixture was added to 1.5 g of 
calcium sulfate and thoroughly stirred again. After the mixture was left 
intact for 5 minutes at room temperature, a piece of tasty white tofu 
having a silk-strained-tofu-like appearance without any stickiness nor 
roughness was obtained.