Kids, there are all kinds of interesting things to think about when someone dips a teabag into a cup of hot water to make their hot tea. Inside a teabag are the crushed up dried leaves of the tea plant. Most of a tea leaf is cellulose, which is the major structural material of all plants. Cellulose is a very long chain (polymer) of glucose molecules and it is does not dissolve at all in water. The tea molecules that will dissolve in water include tannins, flavonoids, and caffeine. In order to separate the molecules you don't mind drinking from the leaf pieces, a teabag is used. Did you ever see a coffee filter? The teabag material is a lot like that. It is a porous paper that can get wet but is strong enough to not break and let the leaves go through. So, in making a cup of hot tea you are also doing an extraction and a filtration - these are two tools that chemists use to isolate compounds. Try it yourself! You can also cut open a teabag and take a look at leaves before and after.
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
Tannins are actually a class of organic compounds, some of which are used to "tan" hides into leather, and some are used in inks and dyes. The brown color of tea is also due to flavonoids, which are organic molecules that are natural pigments. Volatile oils give the flavor. About 2-5% of tea leaves is caffeine. An average 5 oz cup of tea contains 25-75 mg caffeine (some people prefer decaffeinated or herbal teas instead).
The tea leaves are picked by hand, left to wilt, then rolled and dried. If they are allowed to ferment before drying, you get black tea. Partially fermented leaves gives oolong tea, and tea not fermented at all is the so-called green tea. The tea plant is a relative of the camellia, so botanists have named it "Camellia thea". It is an evergreen shrub or tree 9-60 feet high. The first indisputable reference to the medical use of tea is from a Chinese dictionary in 350 A.D., but some folks even say there is evidence that a Chinese emporer used it all the way back in 2737 B.C. And, since it is native to Indochina and India, tea was grown for drinking even before China used it as a medicine.
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Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
October 1998
