The most crucial step in tea processing what defines the categories of tea, is oxidation, a bio-chemical process. The oxidation process what occurs in tea processing is referred to as "fermentation" by the tea industry. It is, in fact a misnomer. Anyway, in processing different types of tea, this step is allowed to occur or partially allowed or totally not allowed to occur. For example, in black tea manufacture, oxidation is allowed to occur by rupturing the cell walls and thereby allowing the enzyme in the tea leaf to react in presence of oxygen. So black tea is fermented tea. In green tea processing, oxidation is not allowed and it is achieved by deactivating the enzyme by steaming or panning the green leaves. It is non fermented tea.The oolong tea which we call semi-fermented tea,is processed by allowing oxidation to some extent and then arresting the process through application of heat. The white tea is least processed, means the enzyme is deactivated by steaming and dried.
From the following diagram, you will get the idea of how different types of tea are processed.
Now let us learn the details about the different methods of Black, Green, Oolong,Yellow and White tea manufacture.