Catechins
Catechins are the flavan-3-ol polyphenols that dominate fresh tea leaf, giving green tea its bitterness and astringency and turning into theaflavins during oxidation.
Definition
Catechins are a family of flavan-3-ols, a class of polyphenol, and the most abundant group of soluble compounds in fresh tea leaf. Green tea, which is heated soon after picking to stop oxidation, keeps most of its catechins; they make up a large share, often more than 10%, of its dry weight. Four catechins account for most of the total: epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG) and epicatechin (EC). The "gallate" forms carry an extra galloyl group and are the most astringent. EGCG is usually the most abundant, often around half of total catechins in green tea. Catechins drive the flavor of unoxidized tea. They produce bitterness, through taste receptors, and astringency, a drying feeling caused when they bind proteins in saliva. Sunlight increases catechin levels, so summer harvests and unshaded leaves taste stronger and more bitter than spring and shaded teas. During processing, catechins are the main raw material for oxidation. When leaf is bruised or rolled, the enzyme polyphenol oxidase combines catechins into theaflavins and thearubigins, the compounds that give oolong and black tea their color and body.
In Depth
Brewing effects: catechins extract faster at higher temperatures and over longer steeps. That is the main reason green tea turns harsh when brewed with boiling water or steeped too long, and why cold brew tastes smoother.
Where the most are: unshaded green teas, especially summer-harvest sencha and bancha, and teas made from Camellia sinensis var. assamica, which generally has more polyphenols than var. sinensis. Matcha delivers a high total because the leaf is consumed whole, though shaded tencha is lower per gram than unshaded tea.
Catechins also bind with caffeine and with milk proteins. Adding milk to tea changes perceived astringency, which is one reason strong, high-polyphenol black teas are commonly drunk with milk. Storage matters too: catechins slowly degrade with heat, light and air, one reason green tea loses its fresh bite within months of opening.
See Also
- Tea Polyphenols
- Tea Chemistry
- Green Tea Composition