The major sources for caffeine are the seeds of the coffee plant (Coffea Arabica), cola
nuts, Mate which is used as tea in Paraguay and Tea leaves (Camellia Sinensis). Three
types of tea are commercially produced from tea leaves (green, oolong and black) which
differ only in their processing methods. To obtain green tea, fresh leaves are steamed to
destroy the natural enzymes that cause fermentation. If however, the leaves are allowed
to ferment an enzymatic oxidation process occurs which gives rise to oolong tea. Longer
fermentation times yields black tea.