TEA 21 



TEA 



(Folia Theae) 



Source, &C. The tea shrub, Camellia Thea, 1 Link (N.O. Tern- 

 strcemiacece) , has been cultivated from time immemorial in China 

 and Japan, and more recently in Assam, Ceylon, Java, &c. 



In the manufacture of black tea the leaves are subjected to pro- 

 cesses that vary somewhat in the different countries. In Assam 

 where much of the tea consumed in England is produced, the leaf- 

 buds together with two or three of the youngest leaves are collected 

 and spread upon trays until they have lost their turgidity. The 

 ' withered ' leaves are then rolled between two flat surfaces worked 

 by machinery, during which many of the cells of the mesophyll are 

 broken, and their sap squeezed out and allowed to come into contact 

 with the air ; at the same time the leaves acquire the twist character- 

 istic of ordinary tea. They are next ' fermented ' by exposing them 

 on mats to the air ; during this process, which is conducted at 

 a temperature of 35-40, the colour changes from green to yellow 

 and finally to coppery red, and the tea acquires its well-known odour. 

 The fermented leaves are dried in a current of hot air, and graded 

 by sifting by which a partial separation into leaf-bud, smaller, and 

 larger leaves is effected. 



The changes that take place during the fermentation are due to 

 the action of an enzyme or more probably mixture of enzymes termed 

 thease. Thease is very active at 54, but is destroyed by a tem- 

 perature of 76-77 ; it oxidises part of the tannin, converting it 

 into a reddish brown, insoluble substance, while at the same time 

 traces of volatile oil are produced and a bitter principle present in 

 the fresh leaves is rendered insoluble. The quality of the tea pro- 

 duced depends largely upon the skill with which this process is 

 conducted. 



In the manufacture of green tea the leaves are subjected to a process 

 of roasting in pans heated by direct fire, in which they are kept con- 

 tinually moving ; they are then cooled, rolled into balls, and allowed 

 to ferment. In this case the preliminary roasting probably destroys 

 some at least of the various ferments of which the thease is composed, 

 the tannin is not oxidised, and the leaves retain their green colour 

 more or less unchanged. 



1 Specific names are written with a small initial letter, except in the following 

 cases : 



(a) When the specific name was formerly a generic name, e.g. Camellia Thea. 



(b) When the specific name is the vernacular name, e.g. Pilocarpus Jaborandi. 



(c) When the specific name is the proper name of a person used as a noun or as 

 an adjective, e.g. Garcinia Hanburyi ; Aloe Hanburiana. 



(d) When the specific name is a noun, e.g. Eucalyptus Globulus. 



