Decoding the mysterious rainbow film on your tea
Occasionally, you might notice a delicate film on the surface of your tea, shimmering like a rainbow. It's unsurprising that such colourful appearances in a cup could arouse suspicion. Where do these colours come from and what do they signify?
Foaming tea and the film on its surface often cause concern. However, their origins are usually straightforward and not a cause for alarm. Although they may look unusual, there's nothing harmful about them. It's helpful to understand their causes, and there are ways to prevent them. You can use this fact to impress your mother-in-law during afternoon tea.
Where does the rainbow film on tea come from?
The film that appears on the surface of tea is different from the film we see on milk, with its sheen similar to spilled petrol. It results from the interaction of tea polyphenols with calcium carbonate present in the water (especially hard water).
The harder the water, the more noticeable the film will be on the tea. You can avoid this by filtering the water before brewing the tea. Adding a slice of lemon can also help reduce the likelihood of this film forming. Although the film may look unsightly, it is not harmful to health and does not significantly alter the flavour of the brew.
Foam in tea
In addition to the rainbow film on tea, foam may also appear. There are several reasons for this phenomenon, one of which is saponins. These are natural chemical compounds found in tea leaves that are responsible for creating foam. Saponins are harmless to our bodies, and the foam created with their involvement is not a cause for concern.
The way tea is poured also affects its foaming. If you pour tea with a strong stream from a height, it introduces more air into the drink, which escapes during brewing in foam. Occasionally, this is even desirable, as in the case of Moroccan tea, which is intentionally poured from a great height.
The type of tea leaves also plays a role in foam formation. Small, loose leaves contain more air, which 'escapes' after pouring the tea with boiling water, resulting in foam. This is still a harmless phenomenon that does not affect the taste and properties of the drink.
