Unveiling the science: Why your tea shows a rainbow hue
Have you noticed a rainbow-coloured film on the surface of your drink? Although it may remind you of spilled petrol, this phenomenon can also occur with tea. At first glance, it might look alarming, but there's no need for concern.
Have you ever wondered why tea creates foam or where the film on it comes from? The explanation for this mystery is simpler than it might seem. It's all about the chemical reactions happening in your cup. While they look impressive, they pose no threat to health.
Where does the foam in tea come from?
If you notice foam after pouring boiling water over tea and are sure it's not from detergent residues, it's most likely due to the presence of saponins in the tea. These compounds are beneficial for health, so there's no need to worry about them, just like the foam they create.
The method of pouring also influences the formation of foam. Pouring tea from a height incorporates air, which then appears as foam. The initial leaves matter as well since fine leaves can trap more air, which is released upon adding hot water.
Rainbow film on tea
The rainbow, iridescent film that sometimes appears on the surface of brewed tea results from a chemical process. The main culprits are polyphenols, natural compounds found in tea leaves that give tea its characteristic taste and colour. These polyphenols react with calcium carbonate, a mineral present in hard water.
The higher the concentration of calcium carbonate in the water, the more pronounced the film will be on the tea. That's why in regions where the water is hard, this phenomenon is more common. Although it looks unusual, the film is completely harmless to health. It doesn't affect the taste or aroma of the tea.
If you want to avoid it, add lemon to your tea. Citric acid inhibits the reaction between polyphenols and calcium carbonate, making the film less visible or preventing it from forming altogether. Filtering the water also helps. This will significantly reduce the amount of minerals that can react with polyphenols, thereby limiting the formation of the film.
