I buy organic, loose green tea from a co-op and found that it's sourced from China. I've never had tea foam before and am concerned that the tea has some kind of chemical on it. The foam tastes very bitter. It made me throw the tea out. I know that the FDA only checks randomly at the port so I'm leary of what's making it foam. Many years of tea making and this is a first.
Does anyone have any experience or answers for this? Thank you!

  • Possible duplicate: cooking.stackexchange.com/questions/22262/… – SAJ14SAJ Apr 1 '13 at 21:06
  • Is it only the tea that's changed, not anything else about your tea-making? Is the tea significantly different from what you've used before in any way? – Cascabel Apr 1 '13 at 21:19
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    Have you seen videos of the Japanese tea ceremony? They use green tea leaves, and part of the ceremony is to whip the tea with a bamboo whisk, creating foam. I don't know what the properties of loose green tea are, or if your green tea is like the tea of the Japanese tea ceremony, but that foam could be a desirable property of your tea. – Gringuita Apr 6 '13 at 9:25
  • Another answer that might help: cooking.stackexchange.com/questions/19373/… – snekse Oct 8 '14 at 22:28

The pouring of water over the tea adds oxygen, which stirs up tannic acid in the tea and causes it to foam. Stirring vigorously also adds air, leading to foam from the tannic acid.

  • Why would this happen only with this particular tea? – Cascabel Apr 3 '13 at 0:43
  • Different teas have different levels. Red tea has less than green tea, for example. As for why it hasn't happened with other green teas, I would guess that variations in how the tea is processed can have an effect. If concerned though, I would recommend getting rid of the tea. It is always better to be safe than sorry. – Kaylie Marie Kipe Apr 3 '13 at 1:17
  • @Debra if what Kaylie Marie Kipe says is true, you might want to try dropping the leaves into the water rather than pouring the water into the leaves and see if that helps with the foaming problem. If it does, it would be really helpful if you commented on the results. – Jay Apr 3 '13 at 6:01
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    Tannic acid does not foam. The surface tension of tannic acid solutions (65 mN/M, source: surfactants in tribology, volume 3) is about the same as that of pure water (60-70 mN/M, source Wikipedia). I couldn't even find foaming index numbers for tannic acid. – rumtscho Apr 3 '13 at 10:35
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    Significant differences in tannin levels would be really noticeable by taste. – Cascabel Apr 6 '13 at 16:43

It's a completely normal chemical reaction. They call it tea scum. It's due to the extraction of amino acids and proteins from the leaves.

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