Process of manufacruring for different types of tea:
All types of tea need to get dried out to a maximum of 3% water content. The first stage of processing tea is withering which is done by transporting fresh leaves as quickly as possible to the processing plant and spreading tea leaves on trays (usually bamboo trays in case of chinese tea) or in troughs in larger facilities and let them dry for 3 hours or so.
This would be the only step for white tea (except that whitering may take longer) before they send tea leaves for further drying for final stage.
The second step is rolling tea leaves to break wall cells of tea leaves. This would initiate reaction of air/oxygen with tea leave enzymes and also let the enzymes break out of tea leaves which contribute to the flavors of the tea.
Green tea at this point takes a different turn. Tea leaves get heated up in pans (pan frying for Chinese green tea) or steamed (Japanese green tea). This is to stop the enzymes to react with oxygen and preserve the colors and original flavors.
Black teas on the other hand go through a process of oxidization (third step) by spreading tea leaves on trays or on concrete floorings for 3 to 4 hours or more to ensure close to 100% oxidization. Tea processors and experts would know when oxidation is completed by aromas of tea leaves.
Oolong teas (besides from getting made of different tea leaves which are usually bigger leaves from lower part of the plant) are partially oxidized at this stage and depending on type of the oolong tea they may get oxidized anywhere from 5% -%95. The less oxidized Ooling teas are more similar to green teas in look and flavors.
Finally tea leaves go through last stage of heating in which they pass the tea leaves through furnaces and heat them up so that final product has less than 3% water content.
Once tea leaves are dry they will preserve their flavors until they are brewed with water where all aromas and flavors unfold.
So which tea goes through least amout of treatment?