Production Method
1. Sprouting. The selected soybeans are first cleaned and soaked in water, then allowed to germinate at a temperature between 32-38°C. After about three days, sprouts of approximately 12.7 to 38.1 mm develop. During the germination process, the soybeans are spread out on a perforated fabric screen or sheet. Water is sprayed over the bean layer every 2 to 3 hours using a sprinkler system to maintain moisture without lowering the temperature below the required level. This ensures optimal growth and prevents any inhibition of sprouting.
The sprouting stage enhances the vitamin content of the soybeans and makes them easier to peel later on. It also helps reduce the strong soybean odor, improving the overall flavor of the final product.
2. Soaking and Washing. At the end of the germination phase, the sprouted soybeans are placed into a sodium hydroxide bath for about four hours. The outer skin, which clings tightly to the beans, is then stripped off. Afterward, the beans are moved to a hydrogen peroxide washing tank, which also helps eliminate unwanted odors. This step ensures that the soymilk and extracted products do not have an unpleasant smell.
After hydrogen peroxide treatment (which must not be delayed too long, as it can reduce the moisture content of the beans), the soybeans are washed continuously in a water tank. A rotating drum or similar container is used, or a hydrostatic method involving high-pressure pumps is applied to stir the beans effectively. This helps remove both residual hydrogen peroxide and any remaining soybean hulls.
During washing, the soybean skins that remain attached are separated and sink to the bottom of the tank through the excretory device. This process is aided by circulating water, and the resulting effluent can be filtered out from the system. The draining device for removing the skins should always be positioned lower than the liquid level in the tank. At the end of each wash, the bath water is drained from the bottom. Every three washes, the water is recirculated at least two times to ensure thorough cleaning.
3. Neutralization. The soybeans are then treated with a weak acid solution, such as hydrochloric acid or Citric Acid, to neutralize any remaining hydrogen peroxide. This process takes about two hours, during which the acid dissolves and neutralizes the chemical. Some unremoved skins may also be removed during this stage. After the acid treatment, the bean skins are drained into the acid bath and sent to the next washing stage.
Following neutralization, the soybeans are washed in one or more fresh water tanks to remove any remaining acid. These washes also help further remove any leftover skins. The final wash solution is tested for pH. If the reading is below 7, additional washing is required until the pH reaches at least 7. If the pH is slightly above 7, a small amount of weak acid can be added to bring it back to neutrality. The soybeans should then be left in the neutral solution for a period to ensure complete soaking.
4. Milling. After the final rinse, the soybeans are immediately sent to a stone mill for grinding. Germinated soybeans are soft and warm, with consistent moisture levels. Grinding breaks down the colloid structure into smaller particles. Once ground, enough water is added to create a smooth soy milk suspension, which is then stirred to maintain uniformity.
5. Cooking and Extraction. The diluted soy milk is cooked either in a pressure cooker or in an open vat. In a pressure cooker, cooking takes about 5-7 minutes at around 121°C, while in an open tank, it lasts approximately 20 minutes at around 102°C. After cooking, the mixture is processed to separate the liquid from the solid particles. This is done using centrifugal extraction methods to obtain a clear liquid.
6. Precipitation and Water Removal. A mixture of calcium sulfide and magnesium chloride is added to the extracted suspension to form curds. The mixture is gently stirred until the curds settle at the bottom. Excess liquid is carefully removed before washing the curd with tap water. The curd is then transferred to a metal mesh basket, where excess water is drained using pumping, siphoning, or impregnation techniques. Further pressure is applied using a cotton filter bag with a movable piston to extract even more moisture. The pressure is maintained for 15–30 minutes to ensure proper drying.
7. Milling and Blending. Once dried, the curd is finely ground using an emulsifying machine or colloidal mill to achieve a smooth texture. The ingredients, such as oils, sugar, salt, vitamins, and minerals, are then mixed in to mimic the composition of natural milk. For fortified milk, additional vitamins like A, D, and C, along with methionine, are included. Before emulsification, the mixture is often separated to prevent bacterial contamination.
8. Sterilization and Homogenization. To ensure safety, the emulsified product undergoes standard dairy sterilization. Following this, the milk is homogenized under high pressure (about 211 kg/cm²) to keep the fat evenly suspended and prevent separation. A standard homogenizer is typically used for this process.
9. Cooling and Packaging. Finally, the homogenized milk is cooled to 4°C and packaged. Fresh milk is stored in regular containers and refrigerated for sale. Canned milk skips the freezing step and is directly sealed in cans, then heat-treated under pressure for 30 minutes, replacing the need for traditional sterilization.
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