Unveiling the mystery. The Truth behind tea's foamy top and oily sheen
Does the presence of foam after brewing tea indicate a problem with the drink? And what about the oily film on the surface of the tea, shimmering like gasoline on water? Should it cause concern?
10:51 AM EDT, April 27, 2024
If you've been wondering about the reasons behind your tea foaming or the origin of that scum, you'll find the explanations simpler than expected. Most importantly, these occurrences are not alarming. Here’s why.
Why does tea foam?
When tea is brewed with boiling water and foam appears on the surface, assuming no dishwashing liquid residue is involved, the foaming is likely due to saponins in the tea. These compounds benefit our health, so there's no reason to worry about the foam they produce.
The method of pouring tea also influences foam formation. A strong pour from a height introduces more air into the beverage, leading to foam (this effect is sometimes desired, as seen in the Moroccan tea tradition of pouring from a height). The size of tea leaves influences this as well; smaller, loose leaves trap more air, which is released upon contact with boiling water, resulting in foam.
Where does the scum on tea come from?
Unlike the familiar scum from heated milk, the scum on tea resembles the shimmering colours of spilt gasoline. This effect results from a reaction between polyphenols in tea and calcium carbonate in water, particularly hard water.
The harder the water, the more pronounced the scum. But again, it's harmless. Filtering the water is advised to enjoy your tea without the oily film. Adding a slice of lemon can also prevent the scum from forming or at least make it less noticeable.
