The basic technological process of traditional tofu production: soybean-cleaning-soaking-pulping-filtering-cooking-solidification-molding-finished product [4]
(1) cleaning: select high-quality soybeans and remove impurities to get pure soybeans. [4]
(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. [4]
(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. However, if it is ground too fine, the cellulose in soybean will enter the soybean milk with protein, which will make the product rough and dark, which is not conducive to the separation of pulp and residue and reduce 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]
(4) Cooking: Cooking is the process of thermal denaturation of protein in soybean milk by heating. On the one hand, it creates necessary conditions for subsequent ordering, on the other hand, it eliminates anti-nutritional components in soybean milk, sterilizes, reduces odor, improves nutritional value and prolongs product shelf life. According to different production conditions, pulping methods can be used, such as earthen stove iron pot pulping, open pot steam pulping, closed overflow pulping and so on. The boiling temperature should reach 65min438+000℃ for about 5 minutes. [4]
(5) Solidification: Solidification is the process that soybean protein changes from sol state to gel state under the action of coagulant on the basis of thermal denaturation. In the production, it is done through two processes: point brain and squat brain. [4]
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 of the network structure of tofu brain, the stronger the interweaving, the better its water holding capacity, the softer 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. [4]
After a period of time, protein's network structure is still not firm, and it needs to stand still for a period of time to complete. According to the different kinds of tofu, the squatting time is generally controlled at 10-30min. [4]
Molding is to put the solidified tofu into a special mold, apply a certain pressure, and squeeze out the excess yellow slurry water, so that the tofu can be closely combined and become tofu with a certain water content, elasticity and toughness. Different products exert different pressures.