Because raw soy milk contains saponins, trypsin inhibitors, and vitamin A inhibitors, as well as a beany flavor. Saponins are highly irritating to the mucous membrane of the digestive tract, which can cause congestion, swelling, and hemorrhagic inflammation, leading to symptoms such as nausea, vomiting, diarrhea, and abdominal pain. It can also inhibit proteases, causing goiter and other toxic side effects; Trypsin inhibitor itself is a protein that can selectively bind with trypsin to form a stable complex, thereby inactivating trypsin. This inhibits the process of hydrolyzing proteins into amino acids, hindering the digestion, absorption, and utilization of dietary protein and reducing the nutritional value of soy milk; Vitamin A inhibitors, in turn, can oxidize and destroy carotene.
In addition, raw soy milk is rich in protein, fat, and carbohydrates, which provides ideal conditions for microbial growth. Therefore, soy milk must be thoroughly cooked. When boiling soy milk, the floating foam must also be completely removed, and then the heat should be reduced to a simmer for about 5 minutes to ensure that harmful substances are completely broken down and destroyed, and that microorganisms are killed. How to boil soy milk at home:
To make full use of the protein in soybeans, it is necessary to eliminate the adverse effects of trypsin inhibitors through processes such as sufficient soaking, grinding, filtering, and heating. When raw soy milk is heated to 80°C to 90°C, a large amount of white foam will appear. Many people mistakenly believe that the soy milk is cooked at this point, but this is actually a "false boil" phenomenon, and the temperature at this stage is not sufficient to destroy the saponins in the soy milk. The correct method for boiling soy milk is to continue heating for 3-5 minutes after the "false boil" phenomenon occurs until the foam completely disappears.
Some people, to be on the safe side, boil the soy milk repeatedly several times. Although this removes harmful substances from the soy milk, it also leads to a loss of nutrients. Therefore, boiling soy milk should be done just right, with the heating time well-controlled.
Special reminder: Although soy milk is good, it should not be consumed in excess. Drinking too much soy milk at once can easily lead to indigestion of protein, causing discomfort such as bloating and diarrhea.