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How can you tell if tea has caffeine?

As an antidote to the wishful thinking about the decaffeinating effectiveness of a 30 second wash I proposed the data presented in "Tea preparation and its influence on methylxanthine concentration" by Monique Hicks, Peggy Hsieh and Leonard Bell which was published in

1996 in Food Research International. Vol 29, Nos 3-4, pp. 325-330. Hicks et al measured the caffeine and theobromine (total methylxanthine) content of six different teas (three bagged and three loose leaf, including black, oolong and green types). They measured caffeine extraction in boiling water at 5 minutes (69%), 10 minutes (92%) and 15 minutes (100%). They replicated all their extractions three times to eliminate error. I extrapolated their data below 5 minutes which gave the following caffeine extraction percentages (averaged over all their tea types and formats; note while loose tea extracted marginally more slowly than teabag tea it made only a couple of % points difference): 30 seconds 9% 1 minute 18% 2 minutes 34% 3 minutes 48% 4 minutes 60% 5 minutes 69% 10 minutes 92% 15 minutes 100%

This was very much at odds with the mythical "30 or 45 second hot wash to remove 80% of the caffeine " advice - as a 30 second initial wash of the tea will actually leave in place 91% of the original caffeine!

Subsequent to that posting I rediscovered a paper by Professor Michael Spiro whose group did some ground breaking physical chemistry on tea. In "Tea and the rate of its infusion" Chemistry in New Zealand, 1981, pp172-174, they disclose caffeine concentration diffusing into water (4g loose leaf - it will have been CTC small fannings type - in 200 ml water held at constant 80 deg C, and stirred with a magnetic stirrer). First data point is at 90 seconds and shows 49% caffeine removed from leaf (i.e. into water). Extrapolating from Spiro's plot gives:

30 seconds 20% 1 minute 33% 2 minutes 34% 3 minutes 76% 4 minutes 85% 5 minutes 88% 10 minutes 99% 15 minutes 100% Thus while a 30 second "wash" under Spiro's rather extreme laboratory conditions (small leaf, loose in the "pot" rather than teabag, at constant temperature and stirred vigorously) leached 20% caffeine rather than just 9% under Hick's more normal steeping, neither of these findings anywhere near match the 80% decaffeination claims of the wishful thinkers perpetuated as an Internet Myth.

Nigel at Teacraft

Reply to
Nigel
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ADDENDUM

Should read "Two minutes . . .64%"

Reply to
Nigel

I don't know how much 30 seconds will.

That's why I'd like to see a plot of residual caffeine given steeps of varying lengths, as well as a plot of residual tannins. So we know just how nonlinear the dissolving is for each.

--scott

Reply to
Scott Dorsey

It's "up to 80%" and extrapolation doesn't work if caffeine is so highly water-soluble that the rate of release decreases dramatically after 30 seconds. We need the actual measurements at the precise points of time.

Caffeine is water-soluble above 175 deg F. Since Spiro's using 80 deg C is right at 176 degrees, I question if a higher temperature, such as the boiling water recommended for the 30-second DIY decaffeinating steep, releases more caffeine than was released at 176 F.

See, it would be easier to accept your Hicks and Spiro defenses if their experiments were conducted using actual measurements at the time and temperature points pertinent to the "myth" because the rate of release at the different temperatures preclude the use of your extrapolations.

Reply to
Bluesea

That raises another point. Does the report say that they used boiling water for black tea and cooler water for green and oolong teas? If so, that might account for the lower amounts of methylxanthines released for the green and oolong teas.

Reply to
Bluesea

I agree that these studies weren't meant to prove what we are using them for, but until you present plausible data of similar credibility, I will continue considering it a myth.

-Brent

Reply to
Brent

I don't mind your considering it a myth in the absence of a quoted study (right now, I'm thinking a 1986 report of a study done by Kaiser Permanente MIGHT be the source), but I surely don't appreciate getting jumped for what is supposedly common knowledge by now by people who use studies that haven't in any way whatsoever supported as yet their stance that it's a myth.

Reply to
Bluesea

You're not getting jumped- it's just that referring to "common knowledge" isn't a valid counter-argument to (at least) plausible scientific data, despite a lack of detail. You say that our data has not supported our conclusions "in any way whatsoever" (a point I would disagree with), yet you do not provide *any* data whatsoever, not even incomplete data, supporting your assumptions. I can think of plenty of times over the course of human history when the common knowledge was blatantly wrong, so it is only reasonable to question it.

-Brent

Reply to
Brent

I disagree, both sets of data look like a classic second order quadratic response to me - and caffeine does not not suddenly become

100% soluble at 176 deg F, neither (in the real world) does a "wash" with water at boiling point take place at 212 F. But, as Professor Ingolfsson remarked (about polar bear ancestry): "This is just how I interpret it. This is science - when you have little data, you have lots of freedom."

However I am mildly surprised that the long term supporters and advocates of this unnatural practice have never actually undertaken (or caused to be undertaken) the key measurements at 0, 15, 30, 45 and

60 seconds.

Nigel at Teacraft

Reply to
Nigel

Does this mean that cold-brewed iced-tea would have less caffeine than hot-brewed? Or does the extended steeping time (hours) allow the caffeine to eventually dissolve in the water even though it is cold?

Alan

Reply to
Alan

Assuming you cold steep at 1 gram leaf per 100 ml water and that avearge leaf contains 3% caffeine I would say yes it will eventually all leach out. I base this on placing 0.3 grams pure caffeine into 1 liter of water at room temperature - it dissolved completely within 2 hours.

Nigel at Teacraft

Reply to
Nigel

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