Saponin

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…