Caffeine is a minor constituent of tea, coffee, and other natural plant materials.
The major constituent of tea is cellulose which is not water soluble. The latter two components can be converted to their calcium salts which are insoluble in water. The caffeine can then be extracted from the water by methylene chloride in almost pure form. Some chlorophyll is often extracted at the same time. Boil the solution on a hot plate for 20 minutes with occasional stirring.