Experimentation in teamaking began during the Ming dynasty (1368-1644). One of the results was the range of teas known as oolong, which is a semi-oxidised variety. Oolong in Chinese literally means "making mistakes" or describes a person who is careless and forgetful. But through trial, error and accidents, exploration during this period brought about marvellous and surprising aromas and tastes. A parallel can be drawn with the discovery of notes and flavours in wine.
Oolong is a big grouping and includes teas from different areas, so covering them all in one column would be impossible. Further complicating the subject is the sheer number of steps in the production process.
Unlike with other teas, such as longjing, which farmers make with the youngest leaves (those at the tips of the plant), oolongs are generally made with the second and third leaves down, which are young but half or almost fully open. The broader leaf allows oxidisation to take place on the edges first and spread inward gradually, creating an intricate profile of aromas and flavours, ranging from flowery to fruity, and with a bittersweet or sweet aftertaste.
After they're picked, leaves undergo a withering process, either in the sun or indoors in a temperature-controlled room. This step helps to demoisturise the leaves and soften them, as well as destroy chlorophyll and so remove undesirable grassiness. Once they are withered, they are allowed to cool off and the remaining moisture distributes itself evenly.
The next step is the "rattling" (or shaking together) of the withered leaves - either by machine or by hand. As they rub against each other, they become bruised, which helps further the oxidisation of the polyphenols in the tea; the moisture is also reduced further, adding to the aroma of the final product. Rattling is essentially what gives oolong leaves their defining colours: green, with red/brown rims.
Once a tea farmer has determined that his leaves have been properly prepared (a process that takes between eight and 10 hours), they are fired for the first time. The high temperature stops any more oxidisation by destroying the enzymes in the leaves. This process also helps to define the taste of a tea; it is a bit like frying vegetables without oil - the freshness and essence of the leaves are preserved.
Next, the leaves are rolled, curled or twisted, again by machine or by hand. This gives them their shape (whether it is the almost bead-like appearance of tieguanyin teas or the long, thin leaves of phoenix oolongs), squeezes out any remaining moisture and presses out oils and juices that impart their flavours during the final stage - baking.
This last step takes place either in electric ovens or over charcoal, with the farmer determining the best temperature and duration for each tea. Baking is crucial as it "sets" the tea, making it as stable as possible - in other words ensuring that there is no moisture left, so the tea can be kept for longer. It is also what really brings out the flavour: underbaked and the tea will be underwhelming, overbaked and it will sting your throat and feel burnt.
http://www.scmp.com/magazines/post-magazine/article/1317436/yum-cha-its-all-making