The science behind tea's mysterious film and foam phenomenon
Tea with a film on top can seem like a drink from another planet. A mysterious coating appears, shimmering. And then there's the foam, which might seem inconsequential but raises suspicions. Has the tea gone bad? Thankfully, it hasn't. These phenomena are natural and even beneficial.
If you've ever looked into a cup and thought, "Hmm, this looks strange," you're not alone. Many people wonder about the changes in their drink when foam or a characteristic film appears after brewing. Although it may appear unappetizing or even cause concern, science offers a simple and reassuring explanation for this phenomenon. So, what does the rainbow-like film on tea mean?
Tea is a true chemical concoction composed of hundreds of compounds. Depending on how you brew it, the type of water used, the quality of the leaves, and the method of pouring, various effects can appear on the surface. But there's nothing to fear. Neither the foam nor the film on the tea is harmful.
The film on tea - where does it come from and what does it mean?
Let's start with the phenomenon that raises the most suspicions: a thin, shiny film that floats on the surface of tea, especially one that has been brewed for a long time and with strong leaves. It looks a bit like an oily spot, shimmers with colours, and resembles gasoline spilled in a puddle. Not pleasant to the eye, but don't worry, it's not a toxin or a by-product of fermentation.
This effect results from a reaction between polyphenols in tea, which are valuable antioxidants, and the calcium and magnesium present in the water. The more mineral-rich the water, the more visible the film on the tea will be. The surface layer forms naturally and does not affect the taste or quality of the drink. However, if you aren't a fan of this sight, you can easily prevent it by filtering the water before brewing the tea or adding a slice of lemon. Why is this helpful? The acid dissolves the compounds responsible for the film on the tea.
Foam in tea is also desirable
Meanwhile, the foam that appears during brewing is due to the presence of saponins, which are plant compounds that exhibit anti-inflammatory properties and support the immune system. These are completely natural substances that can lightly foam when in contact with hot water. They can be found in green tea, yerba mate, and rooibos, among others. The appearing foam indicates that the infusion contains active substances.
The method of pouring also affects the formation of foam. The more dynamically you pour the tea, for instance, from a higher distance, the more air enters the infusion, which further promotes foaming. In some cultures, such as in Morocco, tea is intentionally poured from a height to make the foam visible, treating it as an element of quality.
