> What would make these measurements a lot more useful would be some
> rules, however imprecise, for calculating caffeine uptake according to
> brew temperature and steep time. A year or two ago on RFDT there was
> an interesting thread ("Strong, Cheap, Black Tea") that made some
> progress on this, but I think temperature was ignored.
>
> Are you listening, Dog Ma?


Urrgh - I'm gonna regret this. But so are you, most likely. OK, here's a
chemist's take:

1. You're all correct.

1a. There are a lot of hidden variables here. E.g., the detailed history of
leaf preparation, like CTC vs. wither/toast, probably has a major effect on
the permeability of cell structures in the final product. If we consider
that broken leaf (unlike dust) is still mostly face with relatively little
edge, cell-wall permeability may matter a lotmore than sieve size.

2. That web site (like most) leaves out the most important datum any
scientist would demand first: experimental conditions. Alkaloid-content
measurements on everything from tea/coffee to opium and beyond have been SOP
for over a century. Usual deal is to dry the leaves thoroughly (and, to
pre-empt the question, these methylxanthine alkaloids are reasonably robust
to heat and air), finely grind, and extract with a hydrophobic solvent like
chloroform. Mixed alkaloids are then extracted into dilute aqueous acid,
leaving other organics in the solvent. The aqueous solution is basified,
alkaloids only (less sugars, tannins, etc.) re-extracted, usually into
ether. For tea, what's left is fairly pure theophylline, which can be
weighed up against starting leaf. If a precise number was needed, alkaloids
could be separated by liquid chromatography or fractional crystallization.
The foregoing is a few minutes' work in a going lab. (I know you didn't
really care, but I've done A LOT of these. And it's hard to forget, try as
one might; especially getting refused a coming-home kiss because of the
ether stink on one's breath.)

3. Nowadays, however, it can all be done far more accurately about three
minutes, with complete details of all the main soluble fractions, by
high-performance liquid chromatography.

4. Given the economic value of tea, somebody must have done a decent study
on this. However, as exemplified by an appallingly commercial and
scientifically corrupt article on espresso in a recent issue of Scientific
American, objectivity may be subverted.

5. There aren't all that many independent variables, as these things go. I
suspect that major levers a

- leaf size (e.g., whole, broken, fannings)
- fermentation history (none, halfway oolong, all-black)
- water temperature
- water purity (a low concentration of some ions can drastically reduce
solubility of organics, and possibly cell permeability as well)

all, of course, as a function of steeping time. Naturally, different tea
strains, parts, harvest times and plant maturities will all make a
difference. The above would permit some generalizations for extraction rates
of key flavor and physiology components for all teas.

6. That whole deal is about three days' work on equipment that's standard in
all sorts of academic, industrial and scientific labs. That's if run as a
full-factorial series, which no-one does anymore since experimental-design
software has shown the True Way. It would therefore be a dandy science
project for an advanced high-schooler or community college student. I'd have
done it myself years ago, but I kind of enjoy the mystery. And now I'm out
of the lab, so can't offer.

7. So back to (1) - who cares what the alkaloid or other
bioactive/organoleptic content of a leaf is? We want to know how much comes
out, and when, and how to get the personal best balance. And for that, the
perennial recommendation of {try new things, find people of discrimination
to recommend others, vary conditions to get the best from every tea} can't
be beat.

In a more or less unrelated note, since this post isn't yet long enough, has
anyone ever heard of white tea made by etiolation? (That's light-starving
plants to bleach them, as is done with asparagus.) Might be an interesting
effect. Especially since, or so I assume, many of the things we like best
about tea were put there by God and/or Darwin to keep animals from eating
the leaves.

-DM