Theaflavins and Thearubigins
Theaflavins and thearubigins are pigments formed when catechins oxidise, giving black tea its red-brown color, briskness and body.
Definition
When tea leaves are rolled or cut, the cell walls break and the enzyme polyphenol oxidase meets the leaf's catechins in the presence of oxygen. The reaction joins catechins together into larger molecules. Pairs of catechins form theaflavins; larger, more varied polymers form thearubigins. Together they define the character of oxidized teas. Theaflavins are orange-red compounds that make up only a small fraction of black tea, typically around 0.5-2% of dry weight, but they have an outsized effect. They give brightness to the liquor and a lively, astringent "briskness" on the palate. Tea tasters and buyers often treat theaflavin content as a marker of quality in Assam and Kenyan CTC teas. Thearubigins are a heterogeneous group of red-brown compounds, still not fully characterized chemically, and are present in much larger amounts, commonly 10-20% of dry black tea. They contribute most of the color and the full, rounded body of black tea. Oolongs, partially oxidized, contain intermediate amounts of both, alongside remaining catechins.
In Depth
Visible effects: a bright, golden-red liquor with a colored ring at the edge of the cup indicates good theaflavin content; a dull, dark brown liquor suggests more thearubigins and possibly over-oxidation or poor storage.
Cream down: strong black tea that turns cloudy as it cools is showing theaflavins and thearubigins forming complexes with caffeine that precipitate at low temperature. It is harmless and often a sign of a high-quality, strong tea. Flash-chilling over ice or cold brewing reduces it.
Milk interacts with these compounds as well, which is why the color of milk tea, from pinkish brown to deep tan, says a lot about the strength and type of black tea used. Kenyan and Assam CTC teas, bred and processed for high theaflavin levels, give the bright, coppery color prized in British breakfast blends.
See Also
- Black Tea Chemistry
- Tea Oxidation
- Cream Down