4B2 
THE TROPICAL AGRICULTURIST. 
[JAif. 1, 1902. 
THE FERMENT OF THE TEA LEAF, AND 
ITS Rfc:LATION TO QUALITY IN TEA. 
BY HAROLD H. MANN, B. Sc., 
Scientific Officbr to the Indian Tea Association, 
From the commencement o£ the manufactnre of 
Black Tea in India the nature of the process of 
fermeniatiou, which playa sach an important and 
ebBential part in the manafactare of tea, lias been 
a subject of controversy. In the years before 1880 
for instance, a most energetic discussion took place.* 
On the one hand it was contended, and with good 
show of feason, that the process was merely one of 
incipient putrefaction. On the other, with equal 
vigour and with equal reasonableness, that the re- 
• (alt obtained was entirely independent of any ten- 
dency to rot and, though it might run parallel with 
it, was an entirely independent process. Inasmuch 
as all these views were based entirely on specula- 
tion, and were put forth without an attempt even 
at a microscopic examination of fermenting leaf, 
they naturally led to no better understanding of 
the question. 
MB. bamber's experiments. 
: The investigations of Mr. Baraber were, in fact 
^''tbe first of any importance on th« subject, and he 
has remaiaed practically ever since the standard, 
if not the only, authority on the subject, His in- 
vestigations, nhich it is welt to recall, led him to 
make certain experiments, the following account of 
which I quote from his " Chemistry and Agricul- 
ture of Tea."t 
" The following experiments were made in Assam 
to determine whether the changes, which take place 
during the process, were due to the presence of 
either an organised or soluble ferment or merely to 
oxidation: — 
\st. — Freshly rolled leaf wag placed under a re- 
ceiver, and the air exhausted as completely as possible. 
Little or no change took place, and the leaf at the 
end of 24 hours was still a dull green colour, with 
a. little brown colour on the stems. Admission of 
air or oxygen at this period had no effect on the 
colour, probably owing to the comparatively dry 
bondition of the leaf. 
■ ind. — in this experiment the air was exhausted as 
before, and pure dry oxygen gas admitted ; in half 
an hour the leaf had attained a bright coppery colour, 
and in two hours the whole of the leaf was a uni- 
form dark red, and had gone beyond the stage re- 
quired for ordinary manufacture. Duplicate experi- 
ments were made of the above with similar results, 
and in each case a sample of the same leaf was 
treated in the usual miiuner for comparison with 
the experimental leaf, the flavour of the teas treated 
with oxygen gas did not differ from the ordinary 
teas, but the infusion had a brighter appearance. 
Zrd. — The rolled leaf was treated in vacuo with 
pure carbonic acid, which is an inert gas, with the 
result that at the end of 5^ hours it was still a 
dirty green colour, while a sample treated in the 
usual manner attained the required colour and con- 
dition in B hours. 
ith. — The leaf was exposed to a limited supply 
of air and oven after 20 hours was still of a greenish 
colour, and the tea manufactured from it was very 
pungent, showing that little of the astringent pro- 
perties had been destroyed. 
5///. — The rolled leaf was treated with dry steam 
at a high temperature for a few minutes, and was 
then treated as usual, when it attained a good 
bright colour. 
Qth. — The rolled leaf was treated with air and 
oxygen gas, which gave a bright colour ; the liquor 
was flavoury, but not very pungent, and infusion 
bright. 
• See Tea Cycloptedift, p. 211. 
I Calouttft 18^3. 
" All the above experiments tend to show that the 
change in the leaf in the so-called 'fermentation, 
IS due to oxidation. Microscopic examination has 
failed to show any organism; and the fact that the 
change will take place in an hour or less from the 
breaking of the cells is, I think, conclusive evidence 
that it catuiot be due to the development of living 
organisms.' 
These experiments, thas reported, formed an en- 
ormous advance on the preceding condition of 
ignorance on the question. But yet on careful 
examination it wiU be seen that Mr. Bamber's con- 
clusions were not quite justified by experiments. 
In one case he has since' withdrawn from the 
position he then took up, and has himself announced 
'If- ^'^'^'^"^'^y of an oxidase or soluble ferment to 
which he now ascribes the changes occuring during 
fermentation. He announced this last discovery n 
the following words : — 
" Quite recently I have succeeded after numerous 
attempts in isolatint? a minute proportion of a 
soluble oxidising ferment, somewhat similar to the 
oxidases recently discovered in several plants of 
difilerent natural orders. The substance in qiestion, 
which evidently has a considerable bearing on the 
oxidisiog properties of the tea, apparently does not 
exist in the active form in the fresh green leaf, 
but is changed either during the withering, if the 
leaf is bruised, or d 
the various organic acidd, etc., are liberated from 
the cells. 
The discovery here made has been confirmed by 
one or two independent observers since the time.f 
In another point Mr. Bimber was also in error 
in the views expressed in Iciya. He states that he 
found no hvmg bacteria or other organisms on the 
fermenting leaf, but I have never been able to find 
tea during this process on which a comparatively 
large number of organisms could not be found. 
Wnether they have any part in the process is 
another question, but they are in evidence on every 
sample which I have examined. 
PEHMENTATION at A HIGH TEMPEHATURE. 
But assuming that the conclusions are in general 
correct, certain results would naturally follow. It 
would seem likely that a high temperatuie would be 
the best and quickest for fermentation, since oxygen 
is then most active and the action of stray microbes 
would be entirely eliminated above a temperature 
of 110° F. It therefore seemed advisable to try 
whether fermentation would proceed normally and 
correctly if the mass were raised above that tem- 
perature. Two samples of rolled tea leaf were 
therefore taken, one fermentei at ordinary temper- 
ature (730-740 F.). and the other, with due pre- 
cautions that no drying of the leaf took place, at 
120° F. As a matter of fact to all appearance, 
both coloured normally, that at the higher temper- 
ature a little more rapidly. When apparently ready 
both samples were fired in the same way, and the 
tea examined. In the result it was found that the 
hot fermentation gave a slightly lighter, but a little 
duller liquor. It had a tendency, though not a 
very marked one in the present case, to be soft 
to the taste. 
So far, however, the result is in conformity with 
the idea that bactorial action could have nothing to 
do with the operation, seeing that no organisms 
could be active at the temperature employed and 
yet a fermentation, not quite normal, certainly 
but nearly so, could be carried out. 
oxidation by chemicals. 
It might, however (still on the basis of the above 
assumption that oxidation by contact with oxygen 
gas is all that takes place), be possible to assist 
the action by some substance energetic in giving 
• Report on Ceylon Tea Soils, Colombo, 1900. 
iQni ^S"o«lt«rdl College, Tokio, 
