Kinds of tofu and soymilk
Tofu is the most common and traditional tofu. Its manufacture begins with the coagulation of soymilk.
Hot soymilk is poured into the coagulation vessel (curding barrel) à the coagulant is added à it is agitated so that the coagulant is evenly distributed à it coagulates when left for a specified length of time.
The curds that have coagulated into tofu are ‘trimmed’ with a special tool. This makes it easier to separate the tofu from the water and oil that was not taken into the tofu (the whey is called ‘yu’), and it makes it easier to properly transfer the curds to the forming box in the next process.
Transfer to the forming box and compression
The trimmed curds from which the whey has been removed are transferred to a forming box using a dipper. The forming box has holes in it and a cloth is laid inside it; when it is almost filled with curds a cloth is drawn across it, a lid is put on it and a weight is placed on top to apply pressure. As a result the ‘yu’ comes out through the holes and well-shaped tofu is produced (formed).
Removal from the forming box, soaking in cold water and cutting
The curds (tofu) that solidified in the forming box are transferred to a water tank, left to soak and then cut to a specified size to produce the finished firm tofu. Generally speaking the process then is that, to help it to keep longer, the tofu is cooled all the way through in a water tank (either as it is or in packaging), refrigerated and shipped.
* We are now able to propose an automated system.
There are two kinds of soymilk: an odourless one mainly produced for use in drinks and one with an odour that is produced for tofu making. Since the manufacturing process for these two kinds of soymilk are different, the manufacturing equipment is also different. In particular, the odourless soymilk does not coagulate easily and so it is not suitable for tofu production.
As you will be aware, this is a soft and smooth tofu. Hence, unlike the firm tofu process, it is not agitated and trimmed in the curding barrel, pressure is not applied in the forming box, and the ‘yu’ is not removed. The hot soymilk is poured straight into a forming box that contains the coagulant and has no holes or cloth. The coagulant is evenly distributed by the force of the flow of the soymilk, which is then left for a specified length of time to harden. The subsequent removal from the forming box and soaking in cold water etc. are the same as for firm tofu. Since there is no use of pressure or removal of ‘yu’, thick soymilk is used to form tofu.
Silken tofu solidifies the whole soymilk.
As the name thin-fried tofu suggests, firm tofu is sliced thinly, pressed and dehydrated to make the ‘raw material’ of fried tofu pouches. This is then first deep-fried at a low temperature to expand about three times in size; it is then fried once more at a high temperature (to expel moisture, harden the surface and prevent shrinkage) to produce the finished product.
The tofu to make fried tofu pouches is made by the same process as firm tofu, however it should be made specifically for this – for example, a weaker concentration of soymilk is used for the purpose of the ‘expansion’ etc.
Deep-fried tofu is usually made by draining firm tofu and frying it at a high temperature. It is also known as thick-fried tofu in contrast to thin-fried tofu, as fried tofu pouches are also known. The outer surfaces are fried but the inside is tofu. It can be the same in shape as ordinary tofu but also comes in triangular and other shapes. It is widely used in boiled and stewed dishes and in ‘oden’.
It has the same smoothness as silken tofu and is also known as ‘packaged silken tofu’. In the manufacturing process the soymilk is cooled, then inserted (packaged) along with the coagulant in individual containers, sealed, heated and solidified. The soymilk is cooled because it soon solidifies if it is hot and is thus difficult to package into the containers. Its distinguishing feature is that it is not put into a forming box or left to soak in cold water; in addition, since it is not cut into blocks, other kinds of tofu are also known as ‘cut tofu’ to distinguish them from packaged tofu. Although sausage-shaped containers may also be used, nowadays the same shape as the ordinary square tofu containers are the norm. This tofu came into being along with the advances in mechanization after World War Two, as the manufacturing process is suitable for mechanized production-line mass production.
Another characteristic of this tofu is that it keeps well, since it is sterilized during the heated coagulation after the soymilk has been packaged and sealed.