Barely boiling extraction of caffeine from teabags, standard organic chemistry college lab lesson.
http://www.scienceteacherprogram.org/ch ... l00-2.html
Technique: boiling water extraction (less than 30 seconds) in sodium bicarbonate buffered water. The rapidly extracted aqueous phase is cooled on ice. Counter extraction is performed in a separatory funnel (inverted tear-drop with outlet at narrrow end, inlet at fat end) with dichloromethane, a hydrophobic solvent commonly used in two phase extraction preps. The salt added helps to break water interface emulsions. The DCM hydrophobic ('water-hating') phase float on the water. The funnel is inverted carefully to mix the solvents, and then the organic upper phase is allowed to become clear (free of excess water). It's dried with a dessicant after the lower aqueous phase that has been extracted (water from RAPID tea brewing) is released by stopcock.
The chemistry behind the addition of the weak base (bicarbonate) to the water and its effect on caffeine solubility is explained in this version of the lab, published as a paper in 1995:
http://spot.pcc.edu/~chandy/241/Caffein ... H2CCl2.pdf
structure of dichloromethane
http://www.alanwood.net/pesticides/meth ... oride.html
The DCM is then evaporated in a roto-evaporator (a balloon-like glass vessel, tilted on its side, connect to a vacuum through the top, sitting in a warm bath. It rotates by motor to provide maximum heating surface for evaporation of the solvent.
Still with me here?
The residual powder left is caffeine.
Structure of caffeine:
Two carbonyls, three methyl groups, xanthine parent structure. Not terribly water soluble at room temperature, but much better in boiling water. And very soluble in acidic aqueous solution. Remember this last fact - it's pertinent to the situation of WASHED leaves.
The solubility of caffeine in water in 2.2 mg/mL at 25 deg C, 180 mg/mL at 80
deg C, and 670 mg/mL at 100 deg C. (see psu paper)
The original technical paper, 1996, abstract:
Five minute extraction steps, x3. Loose leaf has half the AVAILABLE caffeine of finely grained tea dust in bags. Little wonder, given the difference in surface area between the two teas. Since total extractable caffeine is reported per mass tea leaf, then the authors used the tea bag tea leaves for their roughly ~30 mg/g average extractable caffeine estimate (33 for black, 37 for green and 24 for oolong).
You get less buzzed from green than black because of the theanine content of green tea.
From the paper abstract, the authors report that ~70% of the total hot water extractable caffeinates in tea bags elutes in the first 5 minutes. Caffeine compounds are sometimes complexed to polyphenols, they would be eluting at >5 minutes range (2nd extraction volume).
Now, something isn't quite right here. We have a VERY typical college organic lab class extracting most of the caffeine in water brought to a boil in a microwave on 'high', for 1 min (2 if it didn't boil in the first minute) total.
The actual amount of time the tea is exposed to very hot water? Conditions: 100-mL plus teabags in a 400 mL beaker, in a 1000-1200 W microwave set on high. With 4 teabags, it will boil relatively quickly, 1 or 2 1-minute cycles. Total boiling time just over 1-min at the outside, much less otherwise.
According to Leonard Bell and student authors, the total extraction at one minute is just under 20 percent. At 30mg total x 4 bags, approximately 24 mg total would be extracted from 4 teabags submerged in boiling water for a full minute.
1 teabag would be just 6 mg of caffeine in 100-mL aliquot of water, and if the equivalent weight of loose leaf tea is used, it would be just 3 mg/g leaf of caffeine released.
Even at a typical extraction time of 3-4 minutes for black loose leaf teas, at 60% extraction but just half of that for our intact leaves, 30% of ~33mg/g, and with a total mass of tea between 2-3 grams per cup of water, we are talking about an average of a bit over 20 mg of caffeine, if the extraction is efficient.
So a quick rinse will get rid of the DUST which carries much more surface for caffeine extraction than whole tea leaf. Intact tea leaves can be washed to remove about much more than 10% of the leachable caffeine (we have 30 mg TOTAL extracted in 2.4 g of tea leaves in 5 min steep time, if you look at the PSU paper cited above, meaning its not a very efficient extraction). Remember that we have half of the caffeine not as easily available in our intact leaves and we are only extracting 50% of the caffeine (maximum extractable).
If you are drinking green tea, theanine is exceptionally effective at countering the effects of blood-pressure and ACTH-inducing effects of caffeine.
If you are drinking oolong teas, the theanine is much less, but so is the caffeine content - about 2/3rds that of black and green tea.
I suggest that the Auburn University paper's results can and have been misinterpreted. Tea leaf washing removes about 20% of the caffeine in the first thirty seconds by removing readily leachable caffeine plus tea-dust present in all tea samples that carries caffeine at twice the concentration of the intact leaf. Removing this mass, even a small amount of it, will remove more than 10 percent of the caffeine. Our Auburn U paper used unwashed tea leaves and teabags.
The remaining caffeine content after a brief wash of whole leafed teas, for most of us, simply isn't enough to induce health problems, even when consumed in several cups worth of tea volume at a sitting.
For those that are caffeine sensitive, look for SFE-extracted decaffeinated teas (or Swiss Water extracted) - these are nontoxic, because the 'solvent' is CO2 under pressure as a liquid. Avoid at all cost less expensive, methylene chloride extracted teas.
The VERY OLD method of leaf washing to remove rapidly eluting caffeine had its purpose, because decaffeination process using solvents wasn't in common industry use until relatively recently (with respect to hundreds of years of tea consumption in the West).