The Supplement to the Tropical Agriculturist 



when tannin is combined with caffeine its in- 

 compatibility with these dietetic substances 

 ceases, and its objectionable retarding action 

 upon digestion accordingly must be modified, 

 if these conclusions ara correct it becomes of the 

 utmost importance to determine whether in the 

 enormously popular beverage tea, caffeine or 

 tannin exists in the free state of mutually 

 combined. 



We have already shown that to a large extent 

 the teas which are regarded as of high quality 

 by the merchant prove to yield infusions con- 

 taining caffeine and tannin in the ratio of I to 3, 

 and the strong inference is that such infusions 

 contain neither free tannin nor caffeine, but 

 neutral caffeine tannate. The merchant's view 

 of quality would thus appear to accord quite 

 happily with physiological considerations. He 

 is guided, of course, chiefly by the flavour of the 

 iniusion, as well as by colour and odour and 

 general appearances. Both tannin and caffeine 

 in the free state have characteristic tastes : the 

 former is astringent and sour, the latter is bitter. 

 A slight excess of caffeine in tea infusion is pro- 

 bably less objectionable than an excess of 

 tannir, since the disagreeable qualities of tannin 

 are more marked. An ideal infusion is oue 

 which contains both caffeine and tannin in 1 to 

 3 proportion — i e., caffeine tannate — neither con- 

 stituent being in excess. This ideal is occasion- 

 ally reached, but, generally speaking, most good 

 teas contain caffeine in slight excess. Caffeine 

 tannate, however, does not possess the qualities 

 of its constituents ; it has a peculiar flavour 

 which is smooth and bland, not unliko a very 

 delicate or lightly infused tea. It must be 

 carefully borne iu mind that in making these 

 deductions we are not considering the chemistry 

 of the leaf, but of its infusion made by pouring 

 400 c.c, of just boiled water upon 5 grammes of 

 tea and decantii g after 5 minutes — a plan sug- 

 gested by the tea-taster's method of assaying tea. 



The Effect of "Stewing" Some Teas. 



The desirable equilibrium may be dis- 

 turbed by vicious treatment even of a good tea" 

 If an Indian tea be boiled long enough or 

 stewed on the hob a point is reached when 

 tannin appears over and above the amount which 

 can combine with the caffeine to form neutral 

 caffeine tannate. Such an infusion presents the 

 objectionable characters of tannin. When this 

 infusion is saturated with ammonium sulphate 

 the caffeine tannate as such is thrown 

 out. If this is filtered off the excess of 

 tannin will be found in the filtrate, from which 

 it can be extracted by ethyl acetate. Thus the 

 five minutes' infusion of an Indian tea showed a 

 total tannin content of 9 - 24 per cent, and caf- 

 feine 3 - 70 per cent. On infusing the same tea 

 for one hour the tannin amounted to 1612 per 

 cent, and the caffeine 4 40 per cent. In the five 

 minutes' iniusion, therefore, caffeine was in 

 slight excess (0'38 per cent.) of the tannin, but 

 in the oue hour's infusion the tannin is in ex- 

 cess of the caffeine by 2'92 per cent. In other 

 words, 4 - 40 of caffeine if combined as tannate 

 would mean in the combination 13"2 of tannin, 

 when as a matter of fact the total tannin found 

 was 16"12 per cent, 



The experience of making wholesome tea 

 seems to have decided upon a limited time for 

 making the infusion. This limit, in fact, appears 

 to us to insist upon the infusion consisting as 

 far as possible of caffeine tannate and upon the 

 exclusion of an important quantity of free tan- 

 nin or caffeine present. But even a five 

 minutes' infusion of some teas may not approach 

 this standard. Indeed, iu view of our work up- 

 on the Bubject we are able to suggest a classi- 

 fication for teas as follows : — 



(rood teas are those which on a five mirutes' 

 infusion yield only caffeine in the form of caf- 

 feine tannate to the infusion, neither caffeine 

 nor tannin being excess ; and badtcas are 

 those which yield on infusion for five minutes, 

 a tea containing in addition to caffeine tannate 

 either caffeine or taunin, but especially tannin 

 in excess. 



It is obvious from this classification that a 

 good tea may be made a bad tea, but a bad tea 

 cannot be made a good tea, except possibly by 

 very skilful blending. Excessive infusion will 

 spoil a good tea, but a short infusion of a bad 

 tea may be as objectionable as an excessive in- 

 fusion of a good tea. On physiological grounds, 

 therefore, the buyer of high-qual ty teas runs 

 less risk of digestive disturbance provided he 

 makes the tea properly. 



These points are interesting in connection 

 with the light types of tea grown in Uhina. The 

 short infusions of these teas commonly contain 

 an excess of caffeine, which probably accounts 

 for their bitterness. They are less rich than 

 Indian Teas, a fact which should make the use 

 of Indian teas more economical, but the best 

 types of them never show the presence of free 

 tannin. A five minutes' infusion of a cer- 

 tain China tea showed a total amount of 

 tannin of 4 60 per cent, and caffeine 2 - 80 

 per cent. On the basis of the one to three re- 

 lationship of caffeine to tannin in caffeine 

 tannate it is evident that in this tea there is an 

 excess of caffeine — viz. : — 1'27 per cent. — for the 

 amount of caffeine that can combine with 4 60 

 of tannin is 153, making a total of 6- 13 per cent, 

 of tannate. As a matter of fact, the amount of 

 caffeine thrown out as tannate when the in- 

 fusion was saturated with ammonium sulphate 

 was 6'48, which requires 162 of caffeine and 4'86 

 of tannin. In the five minutes' infusion, there- 

 fore, there was 1 27 per cent, of caffeine iu 

 excess. On infusing the same tea for an hour, 

 however, the tannin then amounted to 7" 14 per 

 cent, and the caffeine to 3 20 per cent. Caffeine 

 is still in exjess, for the amount combined as 

 tannate is 2 - 38 per cent., giving a difference of 

 3*2 — 2"38=0 - 82 per cent. Some China teas, 

 therefoie, are incapable of yielding free tannin, 

 and these are invariably high priced teas. 



Analyses of Infdsion of Various Teas. 



In the following table will be found a series 

 of analyses of infusions made with Indian, 

 Ceylon, and China teas respectively. The per- 

 centage results are based upon five grammes of 

 tea used in the experiment, the brokers' prices 

 which are attached. It will be noted that, as a 

 rule, the high-priced teas yield infusions con- 

 taining a balance of tannin and caffeine, and in 

 general a larger amount of these constituents, 



