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I have some bottled tea and I noticed that shaking it creates some foamy bubbles that stay for quite a while (at least half an hour if not more). I originally thought it has something to do with my saliva, but then I realized that a brand new bottle of tea also does the same thing. The listed ingredients are water, oolong tea and vitamin C. What could be the reason?

Karsten
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Tipping Octopus
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    I'm inclined to close this as a duplicate of https://chemistry.stackexchange.com/questions/6957/how-does-shock-trigger-nucleation-of-gases-dissolved-in-a-liquid – andselisk Feb 12 '21 at 09:33
  • @andselisk I think the OP does not ask why bubbles are created – what is the nature of that linked question – but why they persist as a minor foamy section. That makes it a different question. Additionally, the tea is not saturated by $\ce{CO2}$ as the other drink is. – Poutnik Feb 12 '21 at 09:47
  • Poutnik is right. The persistance of these bubbles must be due to some surfactant effect. Maybe oolong tea contains an ingredient which acts as detergent and decreases the surface tension of water. – Maurice Feb 12 '21 at 09:59
  • @Poutnik I think the underlying concept is the same, the only difference is the dissolved gas (air vs carbon dioxide). Whether we need a separate question for each and every gas, is an opened question for the community. – andselisk Feb 12 '21 at 10:02
  • @andselisk I think it is not about a dissolved gas in this case at all, but about dispersion of the already present gaseous phase and about foam stabilization by liquid composition. Similarly, the foam on the poured-in Czech beer is more about beer liquid than about $\ce{CO2}$. – Poutnik Feb 12 '21 at 10:05
  • @andselisk I agree with Poutnik and Maurice. The OP is mainly asking about the persistance of the bubbles/foam layer and what, if anything, in the chemical make-up of the bottled tea may be stabilising the bubbles / acting as a surfactant. And the quick answer is : probably the Vitamin C. Ascorbic acid is known to have surfactant properties in a number of solitions. Not published as an answer because I don't have time to go searching for references right now ... – Gwyn Feb 13 '21 at 18:33
  • What other liquids are you comparing it to? Are these other liquids also in a closed bottle. One determinant of bubble lifetime is the humidity of the air. The other is the composition of the bubble. – Karsten Mar 15 '21 at 20:40

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Tea is may be considered as aqueous solution of many different substances extracted from solid tea leaves. (It is not so much about «tea» as in tea, or a tisane.)

In this solution may be ingredients altering the surface tension of water sufficiently enough that air bubbles are trapped for a prolonged time. It could be a component added to act as a preservative, which equally happens to act as a surfactant, or an ingredient intentionally added to ease formation and preserve these bubbles; like the tapioca pearls in bubble tea.

Compounds acting as surfactants may be artificial (like CTAB) made for cleaning, or processes from natural sources, e.g., polysaccharides (like starch), or plain natural. Washing clothes with leaves of climbing ivy, for example works because they contain a small amount of saponins. That a compound acts as a surfactant does not say if it is safe in food, or not.

Buttonwood
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