254 BACTEEIOLOGICAL AND ENZYME CHEMISTBY 



hydrogen peroxide to the unfiltered juice, a blue colour is 

 obtained, but is not developed in the juice after filtering. This 

 indicates the presence of an insoluble peroxidase. 



The flavour of the cocoa appears to be improved by the 

 fermentation process, probably in consequence of the partial 

 oxidation of a tannin present in the bean, but some difference 

 of opinion exists on this point. The flavour is chiefly 

 developed in the subsequent roasting, but the action of the 

 oxidases would seem, from the colour produced, to be a 

 necessary preliminary to this process. 



The Fermentation of Coffee. — The coffee fruit, whose 

 structure is illustrated in Fig. 26, is subjected to a fermentation 

 •similar to the one above described in connec- 

 tion with cocoa ; chiefly in order to loosen 

 the seeds from their surrounding integument. 

 The essential part of this process is a solution, 

 apparently by enzyme action, of the ad- 

 hesive substance between the parchment en- 

 velope and the sUmy layer, so that after 

 the fermented coffee is washed and dried, 

 Fig. 26. the parchment becomes brittle and is removed, 

 Coffee Bean, ^gether with the silver skin, in the process 

 of coffee nulling. This last process is frequently done in 

 London, and not in the country where the coffee is produced. 

 The effect, if any, of the fermentation process upon the 

 flavour of the coffee has not hitherto been fully investigated. 



Tobacco. — The curing of tobacco is agaia a fermentation 

 process. The leaves after gathering are first slightly withered, 

 then ' sweated ' in moderate-sized heaps, and finally fermented 

 in large heaps contaiaing as much as fifty tons of tobacco. 



It has been considered that this fermentation is a bacterial 

 process, and pure cultures have even been introduced in order 

 to impart specific aromas to the tobacco. More recent 



