When brewing tea, a layer of foam may appear on the surface of the tea liquor, known as tea foam. Opinions about this foam have been divided throughout history. Tea sage Lu Yu believed that this layer of foam contained the essence of the tea, but not everyone appreciates this layer of foam. There is even a saying that “foam indicates high levels of pesticide residues.” So what causes the foam? Is there any relationship between the foam in the tea and the quality of the tea? Image
What is tea foam?
The formation of foam in tea liquor is mainly due to the presence of a substance called tea saponin.
Tea saponin, also known as tea sapogenin, is a fine columnar crystal found in the roots, stems, leaves, and seeds of tea plants. Its aqueous solution can produce persistent, soap-like foam when shaken.
Tea saponins are a class of structurally complex glycoside compounds with a bitter and pungent taste. They have strong foaming properties and are not affected by the hardness of the water, so teas with abundant foam tend to have a relatively rich flavor.
In the Wei-Jin era, Du Yu wrote in a poem: “The foam forms like floating Snow, shining bright as if spring blossoms had bloomed.” In the Song dynasty, “tea dueling” elevated the appreciation of tea foam to new heights. People would gather in groups, using black Jian ware bowls to hold the tea liquor and special tools to stir it, creating white foam on the surface. The contrast between the black bowl and the white foam was striking, and the one with the most foam was considered the winner. This shows that in ancient times, people regarded this foam as a form of essence.
Does the amount of tea foam indicate quality?
Some believe that the more foam in the tea, the lower the quality of the tea, suggesting that it may be spoiled. This viewpoint is not entirely correct; the presence of foam in tea does not directly relate to the quality of the tea.
Although tea saponin has strong foaming capabilities, its content in tea is actually very low, and it does not affect the color, aroma, or taste of the tea. Therefore, the quality of the tea cannot be judged based on the amount of foam.
The formation of tea foam is not only due to tea saponin but is also related to the type of tea. For example, teas from hairy varieties, which are typically made from young shoots, contain more internal substances such as catechins. During the rolling process in tea production, these substances stick to the surface of the leaves and dissolve upon contact with water during brewing.
For instance, some high-end ancient Tree teas in Pu'er tea produce foam because they have more leaf hairs; some teas may foam due to insufficient fermentation processes.
Moreover, during the packaging and unpacking process, tea can easily generate fragments. Teas with many fragments will have their effective substances quickly extracted during brewing, and proteins and other substances can cause the tea to foam.
Therefore, the quality of tea is not directly related to the foam.
In the future, when you see foam in your tea, you won't need to worry about poor tea quality or pesticide residues, as it will not affect your health. So, there's no need to worry or overthink when you encounter tea foam while drinking.