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Let's say you have one tea bag and can either brew it in a mug of boiling water, or a larger tea kettle of boiling water. The temperature, steeping time, type of tea bag, etc. are held constant. Assuming you drink all the tea that gets made, would you consume more flavor/caffeine from one method than from the other?

I'm just wondering because even though the amount of tea leaves in the tea bag would be the same, it intuitively seems to me like the water surrounding the bag in the tea kettle would be more hypotonic because there would be more of it compared to the amount of tea, so more tea would come out of the bag overall.

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It seems hard to keep temperature constant. One of the biggest differences is that the larger amount of water is going to cool down more slowly. –  Jefromi Jan 24 at 5:50
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Diffusion is relatively slow, so the water immediately surrounding the bag might not be very different unless you swirl. –  Peter Taylor Jan 24 at 10:43

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up vote 4 down vote accepted

The pot will have more caffeine.

You are right that the concentration of the final solution is determined not only by steeping time, temperature, etc., but also by the amount of water available to dilute the stuff coming out of the tea, including caffeine. It will reach balance earlier with less water. So more water will get more of the different compounds in tea dissolved.

For an empirical observation by somebody surprised by the result, see also this question.

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Your question lumps "flavor/caffeine" together as if they're one item but in fact tea (or coffee) has a variety of chemical compounds that dissolve in water to varying amounts over time (also depending on temperature).

Caffeine in particular is readily soluble in water and I would expect basically all of the caffeine to dissolve quickly, making the total quantity of caffeine similar for a mug or a whole pot. The rest of the "flavor" may take more time and/or be affected by the volume of water.

Edit with a little information about the solubility of caffeine:

  • The solubility of caffeine in boiling water is 66g/ 100mL, which is about 3000x more caffeine than black tea. So even making relatively concentrated tea the caffeine will dissolve quickly and completely. Put another way, you could dissolve all the caffeine in a mug's worth of tea (50mg) into a teaspoon of water (5mL) and still only be at 2% caffeine saturation.
  • The volume and mass of the tea leaves is miniscule compared to the amount of water in a mug, about 100 to 1 by mass. (And some of that tea mass is solute.) There is probably a tiny amount of caffeine left in the tea leaves after dissolution but not a meaningful amount.
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Your answer seems to assume that the saturation of the caffeine solution is independent of other solubles in the water. But it doesn't work that way; having other molecules dissolved in the water will reduce the total amount of molecules of caffeine the water can "hold", meaning that we are talking about saturation limiting the amount of dissolved caffeine, and not the speed of dissolving. –  rumtscho Jan 24 at 13:31
    
@rumtscho: The concentration of one compound may affect the solubility of others a bit, but caffeine is so soluble that I doubt it makes much difference. In fact you can make decaf tea by steeping for 30 seconds or so, discarding the water, and steeping again with new water. The caffeine dissolves much more readily than other compounds. Plus the caffeine concentration of tea is far, far lower than espresso (for instance), so there's no indication that tea approaches the saturation of caffeine. –  Henry Jackson Jan 24 at 15:14
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"I would expect basically all of the caffeine to dissolve quickly" -- This is wrong. sciencedirect.com/science/article/pii/S0021967306022527 sciencedirect.com/science/article/pii/S0308814604007290# –  LordStryker Jan 25 at 4:10

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