Caffeine is a colorless, slightly bitter compound which is present in tea leaf to the extent of 2.5 to 4.5 %. It is an important constituent of beverages such as tea, coffee, and cocoa and is responsible for their stimulation properties. During manufacture, it does not appear to undergo any changes of fundamental importance but it is possible indeed probable that it forms an association with the desirable intermediate products of oxidation, and may protect a part of them by precipitation, so that they do not undergo further changes to complex polymers.
The product of the association between oxidation products and caffeine is soluble in hot water, but separates out on cooling of tea liquors as “cream”. A heavy “cream” on cooling is a sign of a high concentration of red condensation compounds in the liquor. This is one of the aspects of tea manufacture requiring further investigations.