Tea 101
Understanding Oxidation
How tea oxidation works: the enzymatic reaction that creates green, oolong, and black tea from the same leaf. A visual guide to oxidation levels.
Introduction
{{glossary:oxidation}} is the single most important concept in tea. When tea leaves are plucked and their cell walls are damaged — by rolling, bruising, or simply wilting — enzymes within the leaf (primarily polyphenol oxidase) catalyze a reaction between the leaf's {{glossary:catechins}} and atmospheric oxygen. This enzymatic browning darkens the leaf and fundamentally transforms its chemistry and flavor.
The Oxidation Spectrum
Imagine a spectrum from 0% to 100%:
At 0% oxidation (green tea), heat is applied immediately after plucking to denature the oxidation enzymes. The leaf retains its green color, fresh aroma, and high catechin content.
At 5-12% (white tea), minimal handling allows slight natural oxidation during withering, creating subtle sweetness without pronounced grassiness.
At 15-85% (oolong), the tea maker precisely controls the degree of oxidation through repeated cycles of tumbling and resting. This range produces the widest flavor diversity in tea.
At 90-100% (black tea), complete oxidation converts most catechins into theaflavins and thearubigins, yielding bold, malty, brisk flavors.
How Processing Controls Oxidation
The tea maker stops oxidation through fixation — the application of heat to denature the enzymes. In Chinese green tea production, fixation is achieved by pan-firing (chao qing) in a hot wok at 200-300 C. Japanese green teas use deep steaming (fukamushi) or standard steaming (futsu-mushi). The timing of fixation determines the final oxidation level.
Why This Matters for Flavor
Low-oxidation teas taste fresh, grassy, and vegetal because their catechin profile remains intact. High-oxidation teas taste malty, sweet, and brisk because catechins have been converted into larger, smoother molecules. Oolong teas offer the fascinating middle ground, where residual catechins coexist with newly formed oxidation products.
The Health Connection
Oxidation also transforms the health-active compounds. Green tea is richest in {{glossary:egcg}}, the most studied catechin. Black tea's {{glossary:theaflavins}} have their own demonstrated benefits. Both categories are healthy — just through different mechanisms.