Tea World

Lesson 2

Chemical Composition of Black Tea

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As mentioned already, when green leaves are processed, these compounds break down, form complexes and form new compounds. In black tea manufacture, during fermentation a series of biochemical and chemical reactions take place leading to formation of oxidised polyphenolic compounds like thearubigins and theaflavins that are characteristic of tea along with volatile flavour compounds that impart characteristic aroma to tea.

The average chemical composition of black tea (Orthodox and CTC) made from Assam clones is as follows:

Composition Orthodox Teas     CTC Teas
Water soluble solids % 39.52 41.12
Theaflavins % 0.59 1.30
Thearubigin % 6.5 18.00
Total Lipid 3.11 3.68
Carotenoids (µg/g) 215 176
Flavour volatiles   *d 18.40 8.20
Total fibre % 19.35 18.93
Crude fibre% 11.70 11.12
Chlorophyll a mg/g 1.38 0.48
Chlorophyll b mg/g 0.77 0.58

(*d Sum of total area of GC peaks compared to internal standard compounds)

Biochemical Compounds Responsible for Quality of Tea

Different biochemical compounds are responsible for different quality components  of black tea. 

(a) Colour

Compound Colour
Theaflavins Yellowish brown
Thearubigins Reddish brown
Flavonol glycosides Light yellow
Pheophorbide Brownish
Pheophytin Blackish
Carotene Yellow

(b)Taste

Compound Taste
Polyphenol Astringent
Amino acids Brothy
Caffeine Bitter
Theaflavins Astringent
Thearubigin Ashy and slight astringent

(c) Flavour

Compound Flavour
Linalool, Linalool oxide Sweet
Geraniol, Phenylacetaldehyde Floral
Nerolidol, Benzaldehyde, Methyl salicylate, Phenyl ethanol Fruity
Trans-2-Hexenal, n-Hexanal, Cis-3-Hexenol, Grassy, b-Ionone Fresh flavour

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