250 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



Tea. — Tea is produced in two forms for the market, viz., 

 green tea and black tea. In the manufacture of green tea the 

 object is to maintain the colour and to prevent fermentation ; 

 the leaf is therefore roasted immediately after picking and 

 the whole process of manufacture conducted as quickly as 

 possible. In the case of black tea the leaves are dried slowly, 

 and in the course of the process fermentation takes place. 

 This fermentation is a special feature in the formation of 

 Indian black tea, and has been the subject of very interesting 

 researches by Dr. H. H. Mann, to whom the author is indebted 

 for the special information of this section. 



The following processes are involved in the manufacture of 

 Indian black tea : — 



1. Withering. — ^Withering of the leaf, which consists in 

 exposure to the sun on fine basket-work trays. 



2. Rolling. — EoUing by machine, which has the effect of 

 pressing out a certain amount of the juice of the leaves. The 

 soft leaves are often made into balls which are used to absorb 

 the juice. 



3. Fermentation. — These balls are broken up and allowed 

 to ferment and then spread out to dry in the sun. 



4. Firing. — This takes place in a chest of shallow firing 

 drawers, the bottoms of which are made of fine wire gauze. 



5. Sorting. — In this process various quahties of leaf are 

 sorted by sieving, etc. 



Dr. Mann's researches have been concerned primarily with 

 the changes going on during the withering and fermentation 

 processes, and the relation of these to the quahty of the tea. 



The quahty of tea appears to depend on the following 

 factors : — 



(a) The flavour, caused principally by an essential oil. 



(6) Pungency, caused in greatest measure by the unfer- 

 mented tannin. 



(c) Colour of hquor, caused chiefly by the fermented 

 tannin, 



