Green Tea Brewing - Why Foam on Top?

by Margot
(Ajax, Ont. Canada)

Hello Julian,I am one of your long-term customers and am very happy with all the teas I have sampled from you.

A dear friend of mine (a coffee- drinker) made me a present of loose leaf green tea (apparently quite expensive).

I brewed it while she was visiting and found that there was a foam floating on top. What might cause this ? The water I use is always the same, multi-filtered and totally clean.




Margot, yes, I see that quite often too. It could be due to the way I pour tea liquor around, causing foams to form on top.

Also, I think if it is a high quality tea, it could be due to the presence of a compound called saponins, there is some info on this compound here:

Green Tea Nutrition and Calories - Better Than a Vitamin Supplement?

To quote from the above article:

Saponins are found in all teas, and result in the frothing seen in teas like matcha. Tea leaves contain around 0.1% saponins, which give it its strong bitterness and astringency. - See more at:

However, if you see that in a low quality tea, I am less sure of what it could be. Would the presence of pesticide causes foam to form on top? I am not sure, but I am open minded on these things.

Drink quality and enjoy each sip of it.

Hope this helps?


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Sep 15, 2015
A related answer
by: Michael

From StackExchange (though this one is about microwaves, but still):

"When you boil water in a cup in a microwave, it will often boil without forming bubbles, because unlike a kettle with a rough heating element or inner surface, a clean ceramic cup has few nucleation points. Nucleation points allow pockets of gas to form, which become bubbles as the water boils.

When you add the teabag to the hot water, you are essentially introducing thousands of nucleation points very quickly, and so lots bubbles form very quickly - your foam. You should exercise caution when heating water this way prior to adding a teabag, as if you heat it for too long it can superheat, and will boil explosively out of the mug when you add the teabag."

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