(2) Soaking: The purpose of soaking is to make the soybean absorb water and swell, which is beneficial to extract protein from the crushed soybean.
The water absorption rate of soaked soybean is 1: (1- 1.2), which means that the weight gain of soybean is 2.0-2.2 times.
After soaking, the surface of soybean is smooth, without wrinkle, and the soybean skin is not easy to fall off, so it feels firm.
(3) Crushing: After soaking, the protein film of soybean becomes brittle, but in order to dissolve out the protein, proper mechanical crushing must be carried out.
From the perspective of protein dissolution, the more thoroughly the soybean is broken, the easier it is for protein to dissolve.
But if it is ground too finely, the cellulose in soybean will enter the soybean milk with protein, which will make the product rough and black.
But also is not conducive to the separation of slurry and slag, which reduces the product yield. Therefore, the grinding fineness is generally controlled at 100- 120 mesh.
In actual production, the roughness should be properly adjusted according to the variety of tofu, and the residual protein in bean dregs should be controlled below 2.6%.
Crushing with a stone mill, a steel mill or a sand mill. The ground soybean paste was separated by flat screen and horizontal centrifugal screen to fully extract soybean milk.
(4) Cooking: Cooking is the process of thermal denaturation of protein in soybean milk by heating. On the one hand, it creates the necessary conditions for the subsequent paste sorting,
On the other hand, it can eliminate the anti-nutritional components in soybean milk, sterilize, reduce odor, improve nutritional value and extend the shelf life of products.
According to different production conditions, cooking methods such as earthen stove iron pot cooking, boiling steam cooking and closed overflow cooking can be adopted.
The boiling temperature should reach 65min438+000℃ for about 5 minutes.
(5) Solidification: Solidification refers to the thermal denaturation of soybean protein under the action of coagulants.
The process of changing from sol state to gel state. In the production, it is done through two processes: point brain and squat brain.
Dot brain is to add coagulant into cooked soybean milk according to a certain proportion and method, so that the protein sol of soybean can be converted into gel and tofu can be formed.
Tofu brain is composed of soybean protein with reticular structure and water filled in it.
Generally speaking, the larger the mesh, the stronger the interweaving.
The better its water retention, the softer and more tender the tofu made, and the higher the product yield.
On the contrary, tofu is stiff and lacks toughness, and the output of products is also low.
After a period of time, protein's network structure is still not firm, and it needs to stand still and solidify for a period of time to complete.
According to the different kinds of tofu, the squatting time is generally controlled at 10-30min.
Molding is to put the solidified tofu into a specific mold, apply a certain pressure, and squeeze out the excess yellow slurry.
Tofu brain is closely combined to form tofu with certain water content, elasticity and toughness.
Different products produce different pressures.