Oolong is neither a black tea nor a green tea; it falls into its own category of tea. Yet an oolong may end up with more black tea characteristics or more green tea characteristics depending on the direction the tea master takes in the processing of the tea.
Oxidation: Black tea is allowed to fully oxidize during processing, giving the tea leaves their dark color and rich malty aroma they're known for. Green tea is barely oxidized at all, so the leaves keep some of their original green leaf color and fresh-picked flavor. Oolong tea falls somewhere in between and is often described as a partially oxidized tea. But oxidation levels in oolong can vary from 8% to 80% depending on the production style of the tea master. Which is why the flavor profile of some oolongs may lean more toward a fresh green tea (less oxidized) and others toward a malty black tea (more oxidized).The biggest difference between oolong tea and black or green teas? Oxidation and shape.
Shape: Oolong teas are traditionally rolled, twisted or curled into tight balls or thin strands. These artisanal shaping techniques depend on the traditions of the tea master making the tea. Rolling is an important aspect of oolong processing that alters the appearance, color and aroma of the final tea leaves. Depending on how and when the leaves are rolled during processing, the tea master can subtly alter the entire direction of the tea's final flavor.