When making tea, juice, or boiling meat, foam often appears on top. Why does foam form during cooking? Are its components harmful or beneficial to our health? How should we "peacefully coexist" with foam? Foam from boiling congee or noodles
Both rice and flour contain some protein. During the cooking process, some of this protein dissolves into the water, acting as a surfactant. Additionally, some starch from the rice and flour also dissolves into the water, increasing the water's viscosity. A higher viscosity soup helps the foam remain stable, meaning the thicker the soup, the more foam there might be. This foam is harmless to health and can be consumed without worry.
Foam from stewing meat
The foam from boiling meat is slightly more complex. Its main foaming component is also protein. Fat and other components from the meat also appear in the foam. Furthermore, many blood vessels in the meat and some residual blood will also get into the broth, often producing an unpleasant smell and appearance. Therefore, the foam produced in the initial stages of boiling meat mainly comes from the residual blood in the meat, along with some impurities, and it's best to skim it off. If white foam appears later, it is primarily from the protein in the meat and can be kept.
Foam from brewing tea
The substance that creates foam when brewing tea is called "saponin," a type of glycoside. According to current scientific research, it may have antibacterial properties and can inhibit fat absorption. Therefore, you should not remove this layer of foam when drinking tea. However, the amount of saponin in tea is so small that it is far from the quantity needed to produce health effects like antibacterial action.
Juice
Foam from making soy milk
The foam produced when making soy milk is mainly caused by its saponin content. The saponin itself is not a problem, but its presence can cause the soy milk to be full of foam before it actually reaches a boil, creating a false impression of boiling. At this stage, the soy milk contains anti-nutrients 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 produce foam; even fine coffee particles themselves can create foam. The foam in a cappuccino, on the other hand, comes from the milk. Whether the foam is from the coffee itself or the milk, it is not harmful to health and can be enjoyed to your heart's content.
Foam from squeezing fruit and vegetable juice
The foam from squeezing fruit and vegetable juice is similar to the foam in coffee, as it can be produced by a variety of substances. These are all nutritional components of the juice and do not affect your health.