Oxidation

氧化/发酵

Enzymatic browning where polyphenol oxidase converts catechins into theaflavins and thearubigins, transforming the leaf from green to brown-black. Often imprecisely called 'fermentation,' true oxidation is an enzymatic (not microbial) process. Controlled by temperature (20-30°C), humidity (90-95%), airflow, and time (30 minutes to several hours). Zero oxidation produces green tea; partial (15-85%) creates oolong; full oxidation makes black tea. The oxidation level is the single most important factor determining a tea's color, flavor, and body.