Equipment and appliances: stone mill or pulverizer, wooden bucket or crock, cauldron, steamer, etc.
Production method: Put soybeans into wooden barrels or tanks, then pour cold water, and add 22 kilograms of water to each kilogram of soybeans. When soaking, change the water for three times, and stir the soybeans when changing the water, so as to further remove impurities, reduce the PH value, and prevent protein from turning sour. The soaking time is: the peeled soybeans are soaked for 6-8 hours at room temperature 15℃, 5-6 hours at about 20℃, and 3 hours at high temperature in summer. Soybean with skin: Soak for 4-5 hours in summer, 8- 10 hours in spring and autumn, and about 24 hours in winter. Old soybeans can be extended for a period of time accordingly. Soaking in this way can improve the luster, stiffness and decay rate of tofu products.
Grind the soaked soybeans with a stone mill. The stone mill should be ground evenly, and the soybean milk should be even and delicate. In order to fully release protein in soybean, soybean should be ground twice. When grinding for the first time, add cold water and 30 kilograms of water while grinding. After the first grinding, grind soybean milk for the second time, and add cold water 15kg at the same time. At this time, the ratio of soybean to water is generally around 1: 5. After grinding, put the soybean milk into a wooden bucket or vat.
Take vegetable oil or oil residue, accounting for about 1% of soybean, put it in a container, add 10 kg of warm water at 50℃ ~ 60℃, and stir it evenly with a tool. Then pour it into soybean milk to eliminate foam.
Filter immediately after defoaming. Generally, it should be filtered twice and stirred while filtering. During the second filtration, appropriate amount of cold water should be added to wash the bean dregs, so that the soybean milk and the bean dregs can be fully separated. The pores of the filter cloth should not be too large or too thin.
Then pour the filtered soybean milk into the pot at one time, cover it and heat it, and boil it for 2-3 minutes. Be careful not to burn the fire too hard, and stir the pulp with a spoon while heating to prevent the pot from burning. After cooking, pour the soybean milk into a wooden basin and let it cool. When the soybean milk is cooled to about 30℃, take 200 grams of gluconolactone, dissolve it in appropriate amount of water, quickly add it into the soybean milk, and stir it evenly with a spoon. Then pour the semi-solidified soybean milk into an aluminum container or a special plastic food bag and heat it with steam or steamer for about 20 minutes. The temperature shall be controlled between 80℃ and 90℃ and shall not exceed 90℃. Then it is cooled again, and with the decrease of temperature, the soybean milk forms white tofu.
The technological process is as follows: raw soybean → stone grinding → water soaking → pulping → defoaming and filtering → cooking → adding gluconic acid delta-lactone → solidification → heating → cooling and solidification to obtain the finished product.