When making tea, squeezing fruit juice, or boiling meat, foam often appears on the surface. Why does foam form during cooking? Are its ingredients harmful or beneficial to our health? And how should we "peacefully coexist" with foam?
Foam from congee or noodles. Rice and flour both contain some protein, which dissolves into the water during cooking and acts as a surfactant. Additionally, some starch from the rice and flour also dissolves into the water, increasing the water's viscosity. A high-viscosity soup helps foam remain stable, meaning the higher the viscosity, the more foam there might be. This foam is harmless to health and can be eaten without concern.
Foam from stewing meat. The foam from boiling meat is slightly more complex. Its main foaming component is also protein. Fat and other ingredients from the meat also appear in the foam, along with many of the meat's blood vessels and residual blood, which often produces an unpleasant odor and appearance. Therefore, the foam that forms at the beginning of boiling meat mainly comes from residual blood water in the meat, along with some impurities, and it's best to skim it off. If white foam appears afterwards, it is primarily from the protein in the meat and can be kept.
Foam from tea. The substance that creates foam when brewing tea is called "tea saponin," a type of saponin. According to current scientific research, it may have antibacterial properties and can inhibit the absorption of fat. Therefore, you should not remove this layer of foam when drinking tea. However, the amount of tea saponin in tea is so small that it is far from the quantity needed to produce health effects like antibacterial action.
Foam from soy milk. The foam produced when making soy milk is mainly caused by its saponins. The saponins themselves are not a problem, but their presence can cause the soy milk to be full of foam before it reaches a boil, creating a false impression of boiling. At this stage, the soy milk contains anti-nutritional factors like protease inhibitors, which can affect protein absorption. Therefore, you can add a little oil to defoam, or heat it over low heat until the foam disappears, and then bring the soy milk to a true boil.
Foam from coffee. There are many components in coffee that can create foam, and the fine coffee particles themselves can also produce foam. The foam in a cappuccino, on the other hand, comes from the milk. Whether the foam is from the coffee itself or from the milk, it is not harmful to health and can be enjoyed without reservation.
Foam from squeezing fruit and vegetable juice. The foam from squeezing fruit and vegetable juice, like the foam in coffee, can be produced by various substances, all of which are nutritional components of the juice and do not affect health.