When hot water is used to steep Tea leaves, foam often rises to the surface. After the brewed tea cools down, a thin film may form on top. Some people worry that this foam and film are indicative of pesticide residues or poor tea quality. Food science experts explain that the substances causing the foam in the tea have antibacterial properties, known as tea saponins. The film that forms is composed mainly of oxidized polyphenols, calcium carbonate, and other salts. Consumers need not be concerned about the safety of these elements when drinking tea.

Professor Liu Shaowei, a member of the expert panel of the Shanghai Association for Food Safety, told China Consumer News that the foam produced when tea is steeped is primarily due to tea saponins and protein-like substances. Tea saponins, also known as tea saponins, are compounds that are difficult to dissolve in water. Based on current scientific research, tea saponins have antibacterial effects and can inhibit fat absorption. However, the amount of tea saponins in a Cup of tea is too small to expect any significant antibacterial effect.

The presence and quantity of foam in the tea primarily depend on the tea plant variety and the shape of the finished tea. Different tea varieties contain varying levels of tea saponins, and the shapes of the tea leaves differ, which can influence the amount of foam produced.

In general, teas from varieties with many fine hairs (such as some Jin Junmei, Fuding Dabai, and Fuding Dahao) are mostly made from tea buds, which have higher contents of tea saponins and polyphenols. If the tea is rolled vigorously during processing, causing the internal substances to be released and stick to the surface of the leaves, it will produce more foam when steeped.

Additionally, some tea materials are finely ground, such as broken black tea, or the tea may generate small fragments during packaging and transportation. When steeped, the internal substances of these teas are effectively released, leading to the formation of foam.

Similar to the foam caused by tea saponins, the film that forms on the surface of cooled tea is mainly composed of oxidized polyphenols, calcium carbonate, and other types of salts. Factors such as water hardness, pH, tea concentration, and brewing temperature all influence the formation of the film.

For example, calcium ions and bicarbonate ions in the water are key factors in inducing the formation of the film. As long as both are present, a film will form. However, if completely pure water is used to brew tea, no film will appear after cooling.

The type of tea also affects the formation of the film. Generally, black tea is more likely to form a film, while White Tea, yellow tea, Green Tea, or lightly processed Oolong tea rarely form a film after cooling. This is because black tea undergoes longer fermentation and a higher degree of oxidation compared to other tea varieties.

Some people worry that the foam or film might be pesticide residues. Professor Liu Shaowei explains that 98% of the pesticides permitted for use in tea production in China are lipophilic substances that do not dissolve in water and thus cannot form foam or a film upon cooling. There is also no experimental evidence linking pesticide residues to the formation of tea film or foam.

In summary, neither the foam nor the film is anything unsanitary or indicative of pesticide residues. There is no need to remove them when drinking tea. (By Li Jian, reporter)