Theine has been found in nature in but a few plants, as in tea, in coffee, (then termed caffein), in Mat'e (Paraguay or Brazilian tea), and in the Kola nut of Africa. A very similar principle, having analogous properties, but containing more nitrogen, exists in cocoa, (theobroma).
Theine, when isolated by heat from the tea leaf or infusions, condenses in minute white needles or crystals, having no odor and but a faintly bitter taste. In manufactured tea leaves, theine constitutes from one to five percent. of their weight. According to Professor Johnston, three or four grains per day of this substance may be taken without injury by most persons; or such quantity as would be contained in half and ounce of Chinese black tea. Indian (Assam) tea and Ceylon tea, being stronger in theine, would suffice in lesser quantity.
Theine is soluble in about 100 parts of hat water. It vaporizes at 185 degrees C. or 365 degrees Fahr., hence it is not driven off by continued boiling of tea infusion.
W. Dittmar found by experiment that prolonged steeping of tea leaves up to ten minutes increased the proportion of theine in the infusion. His results are as follows:
STEEPED 5 MINUTES.
Average of 8 samples Chinese tea:
Theine, per cent infusion—2.58 Tannin—3.06
Average of 6 samples Ceylon tea:
Theine—3.15 Tannin—5.87
Average 12 samples of Indian tea: