All teas come from the leaves of the same plant, Camellia sinensis. It is how the leaves are processed that determines the category to which the tea will belong.
The six main tea categories are: white, green, black, yellow, oolong and pu-erh (post fermented) teas. To better understand their manufacture, let us explain in simple terms, the process of oxidation and its role in the production of the various types of tea.
Bite into an apple and leave it exposed to the air. Pretty soon it goes brown. The oxygen in the air is reacting with the exposed juices and enzymes of the apple. This is oxidation. The same principle applies to a tea leaf. If one is picked, dried and then rolled (or bruised) to expose the juices it will also begin to oxidise and turn brown. Treated further it will become fully oxidised black tea.
If you pick the same leaf, dry it and apply heat to deny any oxidation, green tea will result. Placed in storage and allowed to mature, the green tea leaves will turn into yellow tea. Oolongs are somewhere between green tea and black tea, made by allowing some oxidation to occur, anything between 10 and 80 percent. In white tea production, the leaf is shade dried and handled gently so as to prevent rolling and exposure of the juices. Oxidation is therefore kept to a minimum.
Pu-erh tea starts off like green tea but undergoes true fermentation in its change to its final state. Fermentation is anaerobic in that air is not required for the reaction as opposed to oxidation which of course requires the presence of air. Fermentation occurs when the leaves are piled up and left to undergo change from within the pile. The pu-erh, both raw and cooked types, will continue to ferment while stored, for anytime between five and fifty years.
Contrary to what many people believe, herbal and fruit infusions cannot be categorized as tea, as they contain no Camellia sinensis. Rather, they are best described as tisanes possessing excellent qualities of their own.
Hence, the six main tea categories all originate from the same plant, Camellia sinensis. It is how the leaves are processed and treated which ultimately distinguishes the different tea types.