Black tea, green tea, and oolong tea—while they may seem completely different, they all come from the same "tea plant (scientific name Camellia sinensis)". The difference arises from how much fermentation (more accurately, oxidation) the harvested leaves undergo. The degree of fermentation significantly alters the color and aroma of the tea.
Classification of Tea by Fermentation Level
| Classification | Fermentation Level | Representative Teas |
|---|---|---|
| Unfermented Tea | None | Green Tea (Sencha, Gyokuro, Matcha) |
| Partially Fermented Tea | Stopped partway | Oolong Tea, Baozhong Tea |
| Fermented Tea | Fully | Black Tea |
| Post-Fermented Tea | Fermented by microorganisms | Puerh Tea |
What Happens During "Fermentation"?
In the context of tea, fermentation refers not to microbial fermentation like that of natto or yogurt, but rather to oxidation caused by the action of oxidizing enzymes present in the leaves. This is similar to how the cut surface of an apple turns brown. When the harvested leaves are withered and rolled to activate the enzymes, the green components oxidize and turn reddish-brown, creating the unique color and aroma of black tea.
- Green Tea: Immediately heated to stop the enzymes → Retains green color and freshness.
- Oolong Tea: Oxidized partway and then heated to stop → A floral aroma that is a blend of green and black tea.
- Black Tea: Fully oxidized → Red liquor color with rich body and sweet aroma.
Different Varieties from the Same Plant
Even within the same tea plant, there are two main varieties: Chinese Variety (small, cold-resistant, delicate aroma, suitable for Darjeeling and Chinese teas) and Assam Variety (large, robust, produces a strong body, suitable for Assam and Ceylon teas). The uniqueness of each tea-producing region is determined by the combination of these varieties with climate and production methods. For more on the differences between regions, please check Learn About Tea by Region.