CAMELLIA 



THEA 



Chemistry 



THE TEA PLANT 



Tea Kefnse. 



Tannin. 



Estimation. 



Tannin 

 Oxidised. 



Expressed 

 Juice. 



Enzyme 



The total quantity of caffeine present in tea varies from 3 to 5 per cent., 

 and this quantity undergoes no change during the processes of manufacture. 

 On the other hand, the ease with which it is extracted is by no means so 

 great in the fresh leaf as in the finished black tea. Nanninga (Mede- 

 deelingen uit 'slands Plantentuin, 1901, xlvi., 3) gives figures, for in- 

 stance, where the quantity extracted by the same method increased 

 from 2 '51 to 3 '11 per cent, in passing from fresh leaf to fermented and 

 finished black tea. 



In this connection it might be pointed out that tea refuse is practically 

 the only commercial source of caffeine. From this it is, however, pro- 

 duced at the rate of 30,000 Ib. yearly, or thereabouts, the manufacture 

 being carried on in England, Germany, France, and America. Recently 

 successful attempts have been made to extract the caffeine on a com- 

 mercial scale, from the tea on the spot in India, and it is probable that 

 this manufacture, as an attachment to tea estates, may take a considerable 

 development in the tea districts of the country. 



The third constituent of great importance in the tea-leaf and also in 

 the tea is the tannin. A great deal has been written of the evil effect of 

 the tannin in tea, most of which is, however, not based on exact experi- 

 ment, but rather on general impressions. Whatever be its physiological 

 action it is certain that it is the constituent which gives tea its pungency, 

 and, in its form oxidised during fermentation, it also imparts the colour 

 to infusions of tea. In short, from a commercial point of view the 

 value of Indian tea, in so far as it is determined by pungency and 

 colour of liquor, varies with the quantity of tannin easily extractable 

 by water. 



The quantity of tannin is, however, very variable, and during manufac- 

 ture alters to a very great extent. If we take the quantity extracted by 

 water in ten minutes at 212 F. from finely divided tea as the standard, 

 the following represents the reduction which normally takes place ( 

 determined by hide powder) during the manufacture. All the figures 

 are calculated on the dried material. 



(1) (2) (3) 



Tannin in leaf as rolled .. .. 15-51 .. 16-90 .. 16-98 

 Tannin in finished black tea .. 12-94 .. 12-53 .. 13-78 



The colour of the liquor given by fermented tea is due to the oxidised 

 tannin produced during the fermentation process, and in practice it 

 always becomes a question of skilful management to know how far " to 

 sacrifice pungency to colour " ; in other words, how much of the tannin is 

 to be allowed to oxidise during manufacture. 



In a normal fermentation conducted below about 82 F., the oxidation, 

 produced by the enzyme already mentioned, is a perfectly definite and 

 complete operation. All the tannin pressed out of the cells and brought 

 in contact with the air is oxidised in from four to six hours according to 

 the temperature. The relative colour and pungency of the final product 

 depend, if a complete fermentation is allowed, on the amount of rolling 

 and hence of juice expressed. If the process is conducted much above 

 82 F., other oxidations take place, independent of enzyme action, and 

 these give the tea a " stewed " taste, while rapidly lowering the tannin 

 percentage without increasing the colour of the infusion. The explanation 

 is probably that the fermentation of the tannin by means of the tea oxidase 

 (enzyme) only carries the oxidation one stage forward, and though the 



