There are two types of decaffeination processes used in tea.
     One is accomplished using ethyl acetate, an organic
     [chemical] solvent, and the other is with carbon dioxide. With
     ethyl acetate, the tea is moistened and the solvent is passed
     through the leaves. As it passes through, the ethyl acetate
     takes the caffeine with it. Ultimately, thetea is heated to
     remove [most] of the remaining chemical residues and then is
     dried. In carbon dioxide decaffeination, moistened tea leaves
     are put under heat and pressure and treated with carbon
     dioxide gas. The carbon dioxide mixes with the caffeine, and
     when it is released to the atomsphere, it takes the caffeine
     with it.

     Both of these options are successful in removing caffeine form
     tea leaves, but only the carbon dioxide process preserves the
     majority of the medical integrity. EGCG, along with other
     medicinally significant flavonoids found in tea, is water
     soluble. Therefore, any decaffeination process involving water
     will remove these components at the same time it removes
     the caffeine. Ethyl acetate does this when it bonds with the
     caffeine. Carbon dioxide, however, does not interfere with the
     flavonoids.

from http://www.tripleleaf-tea.com/tripleleaftea/understand.htm 3 July 2000