How do the leaves of one plant (Camellia Sinensis) become 6 different types of tea? The secret is in the process. After tea leaves are plucked, they are allowed to wither. This step removes some initial moisture. Oxidation follows when the fresh leaves are exposed to air. Just like an apple slice, the tea begins to turn brown. The level of oxidation determines the type of tea. For example, black teas are 100% oxidized while green teas are not oxidized. The oxidization process helps develop the tea's aroma, color, and flavor.