154 FLAVORING AND BEVERAGE PLANTS 
quantity it often has upon the nervous system a marked 
effect, which may be injurious or beneficial according to 
circumstances. The coffee ‘‘bean”’ contains about 0.5-2% 
of caffeine, dried tea leaves about 1-3%. Theobromine, of 
which there is about 1.5% in the cacao seed, is found to be 
scarcely soluble in the fluids of the body, and thus exerts 
little if any effect. 
The most active constituent of each of the three beverage 
plants we are considering is the aromatic substance to which 
its peculiar flavor is due. In black tea there is about .5%, 
and in green tea about 1% of a volatile oil which is mainly 
developed during the curing or preparation of the leaves for 
market. The commercial value of a tea depends mainly 
upon the flavor imparted by its volatile oil. This flavor is 
carefully tested by experts who are known as ‘‘tea-tasters,”’ 
although curiously enough they smell rather than taste the 
samples submitted to them. Even so, the effect of the vola- 
tile oil upon the nervous system is so powerful as to cause 
giddiness and headache if the ‘‘tasting”’ be continued more 
than a few hours a day; and it is said that the most vigorous 
cannot pursue the work for many years without suffering 
serious consequences. The peculiar aroma of coffee is not 
found in the raw “‘bean”’ but is developed during the process 
of roasting; that of cacao arises during the process of fermen- 
tation which the seeds undergo before they are ready for 
market. In coffee the aromatic constituent is hardly as 
powerful as in tea, while in cacao it is so mild that vanilla and 
various spices are added as flavoring to make chocolate. 
Finally, mention must be made of an astringent constituent 
belonging to the class of substances known as tannins. This 
forms about 10% of dry tea leaves. It is similar to the sub- 
stance extracted from bark for tanning leather. Black ink is 
commonly made by combining tannin with a substance con- 
taining iron. When taken with food in considerable quanti- 
ties this astringent interferes with digestion. Prolonged boil- 
ing extracts it in large amount from tea leaves; consequently 
tea so prepared is most injurious. Steeping for a short time, 
on the contrary, removes but little of the tannin, while it ex- 
tracts practically all of the exhilarating and aromatic constit- 
