The caffeine, tannin and essential oil, create, respectively, the physiological effects, the strength and the flavour of tea. The commercial value of tea, however, appears to depend on the essential oil and aroma, not on the amount of caffeine, tannin or extract.

The following is suggested as a typical analysis of an average sample of black tea in percentage.

Albuminous matters(fiber of the cells) — 24
Gummy matters — 4%
Cellulose(A complex carbohydrate present in the cell walls of plant cells) — 20%
Chlorophyll and wax — 2%
Caffeine — 3% (one teacup of the beverage contains 60 to 90 milligrams of caffeine)
Tannin — 10%
Essential oil — 0.75%
Resin — 3%
Mineral matter — 6%
Water — 7%

Caffeine is an alkaloid of tea; in large quantities it is a poison, but in smaller quantities, it acts as a stimulant. It exists in greater percentages in Indian and Ceylon teas than in those from Java, and is lowest in Chinese and Japanese teas.

Tannin is a hardening and astringent substance and in large quantities impairs digestion. Prolonged infusion increases the amount extracted. It has a bitter taste and is what is balanced in the brewing time, to get the most of the oil and caffeine and the least amount of tannin.

The essential oil of tea has a citron yellow color; it is lighter than water and possesses the distinctive odor of tea.