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Decaffeinating tea
Jul. 4th, 2019 07:47 amIn response to my post about getting to sleep, someone has kindly pointed out that the common wisdom regarding water decaffeination of tea is bunk. (My wife had heard, and told me, that the first minute of steeping removes 90% of the caffeine, which is clearly quite wrong.)
This page has tables showing the caffeine found in first, second, and third brewings of various kinds of tea, where each steep is three minutes long.
Normally, Assam (our tea of choice) wants to steep for four minutes. However, my wife decaffeinates her Assam for one minute, then steeps it for six minutes (to make up for the flavor loss) before we make second pot tea (another six minute steep). The tl;dr of the following is that my second pot tea appears to contain 5.3% of the caffeine of fully caffeinated first pot tea.
Dr. Branan's test has the first pair of three-minute steeps showing a 70% reduction in caffeine per serving (86.3 mg reduced to 25.75 mg), and the second pair showing a 67% reduction (25.57 mg down to 8.5 mg). Using the latter ratio (as it involves the time frame we're concerned with), we can estimate that each minute takes 31% of the caffeine remaining in the tea leaves out into the tea. Summing the series gives us 38.44 mg of caffeine remaining in the leaves at the three minute mark. So the caffeine in the leaves at the seven-minute mark should be 5.87 mg, and at the thirteen-minute mark should be 0.64 mg. The difference (what's in my second pot tea) is 5.23 mg of caffeine.
By a similar calculation, if the initial three-minute test had been the standard four minutes, it would have contained 98.17 mg. My second pot tea thus appears to contain 5.3% of the caffeine of fully caffeinated first pot tea.
The one minute mark, interpreting geometrically from the ratio of the caffeine in the first and second pots, should leave 86.09 mg of caffeine in the leaves, of which 80.22 mg comes out in the first six-minute steep. This is 81.7% of the caffeine found in four-minute, first pot tea.
However, both of these figures are really lower than shown by an unknown amount, because the initial minute of decaffeination involves vigorous stirring to increase the dissolution of caffeine. We have no data on this effect.
(Note that I used more significant figures in my calculations than I show here, so final digits might appear to be off by one. This doesn't matter at all, because the experimental margin of error has got to be way too high to justify even the significant figures that I show.)
This page has tables showing the caffeine found in first, second, and third brewings of various kinds of tea, where each steep is three minutes long.
Normally, Assam (our tea of choice) wants to steep for four minutes. However, my wife decaffeinates her Assam for one minute, then steeps it for six minutes (to make up for the flavor loss) before we make second pot tea (another six minute steep). The tl;dr of the following is that my second pot tea appears to contain 5.3% of the caffeine of fully caffeinated first pot tea.
Dr. Branan's test has the first pair of three-minute steeps showing a 70% reduction in caffeine per serving (86.3 mg reduced to 25.75 mg), and the second pair showing a 67% reduction (25.57 mg down to 8.5 mg). Using the latter ratio (as it involves the time frame we're concerned with), we can estimate that each minute takes 31% of the caffeine remaining in the tea leaves out into the tea. Summing the series gives us 38.44 mg of caffeine remaining in the leaves at the three minute mark. So the caffeine in the leaves at the seven-minute mark should be 5.87 mg, and at the thirteen-minute mark should be 0.64 mg. The difference (what's in my second pot tea) is 5.23 mg of caffeine.
By a similar calculation, if the initial three-minute test had been the standard four minutes, it would have contained 98.17 mg. My second pot tea thus appears to contain 5.3% of the caffeine of fully caffeinated first pot tea.
The one minute mark, interpreting geometrically from the ratio of the caffeine in the first and second pots, should leave 86.09 mg of caffeine in the leaves, of which 80.22 mg comes out in the first six-minute steep. This is 81.7% of the caffeine found in four-minute, first pot tea.
However, both of these figures are really lower than shown by an unknown amount, because the initial minute of decaffeination involves vigorous stirring to increase the dissolution of caffeine. We have no data on this effect.
(Note that I used more significant figures in my calculations than I show here, so final digits might appear to be off by one. This doesn't matter at all, because the experimental margin of error has got to be way too high to justify even the significant figures that I show.)
