Oxidation Control

Oxidation is the biochemical process where polyphenol oxidase enzymes in damaged tea cells convert catechins into theaflavins and thearubigins, darkening the leaf and transforming its flavor from vegetal to fruity, malty, or earthy. Tea makers control oxidation through three variables: physical damage to leaf cells (through rolling, tumbling, or bruising, which exposes enzymes to substrates), environmental conditions (temperature, humidity, and oxygen availability), and duration before kill-green. Green tea undergoes kill-green immediately after withering, stopping oxidation at 0-5%. White tea is allowed to oxidize naturally during withering (5-15%) without deliberate bruising. Oolong spans the widest range: lightly oxidized varieties (Baozhong at 15-20%) retain floral freshness, while heavily oxidized types (Oriental Beauty at 70-80%) develop honey and fruit character. Black tea is rolled aggressively to maximize cell damage, then allowed to oxidize fully (90-100%) before firing. The skill of oxidation control is what separates a great tea maker from a mediocre one — the difference between a transcendent Tieguanyin and a forgettable one often comes down to stopping oxidation at precisely the right moment.