Improvements in the Manufacture of Black Tea from the Green Tea Leaf.
Year: 1897

page_text: Date of Application, 15th Jan, 1897.
Complete Specification Left, 15th Oct., 1897-Accepted, 20th Nov., 1897
PROVISIONAL SPECIFICATION...
Improvements in the Manufacture of Black Tea from the Green
Tea Leaf.
I, SAMUEL CLELAND DAVIDSON of Sirocco Engineering Works, Belfast, Ireland,
Merchant, do hereby declare the nature of this invention to be as follows -
According to the ordinary method of manufacturing black tea from green tea leaf,
the green leaf is first "withered" (as it is technically termed in Tea Factories), or
limped by being spread on mats or racks of trays, and subjected thereon or in some
other suitable way to the action of the sun or to the currents of cold or warın dry
air. During this operation the leaf usually parts with from about 25 to 50 per
cent of moisture, and it feels soft and flaccid. when a mass of it is grasped in the
hand. The leaf when thus withered is then rolled as the second stage. in.. its
manufacture; this rolling bursts the cells, so that the juices; exude over the
surface of the leaf, and render it a wet or moist mass.
This moist mass of rolled leaf is then as the third stage of its manufacture spread
in layers, and left so as to be more or less exposed to the atmosphere, to undergo what
is ordinarily termed "fermentation," and which generally takes from two to four hours
to accomplish, according to weather and atmospheric conditions. During this operation
the leaf changes from green to a brownish or a copper color. Finally, after being
then usually subjected to a second rolling, the leaf is dried, and during this operation
it turns black, the resulting product being what is known as "black tea."
1
During the above described process of fermentation which the leaf undergoes after
it has been rolled and the cells burst so that the juices exude over the surface of the
leaf, the juices are consequently in more or less direct contact with the atmosphere,
and under these circumstances absorb oxygen therefrom with avidity, the effect of
which is that the tannin and other properties thereof rapidly undergo changes, some
of which have a deteriorating effect on the resulting product of black tea.
It is, however, an essential part of the manufacture of black tea that some of the
alterations in the properties of the leaf which are indicated by its changing color as
above described, from its originally bright green to a more or less brownish hue,
before being dried, should take place, and I have now ascertained, as the outcome of
a long series of experiments, extending over many years, in various modifications
and methods of withering and fermenting tea leaf, that a better product of black
tea is obtained when this change of color is effected in the leaf while the cells are
still unburst (i.e. prior to the rolling process), and when their contained juices are
consequently to a considerable extent protected from the oxidizing influences of
the atmosphere by the unbroken (though it may be bruised) cell tissue and
parenchyma of the leaf, in .contradistinction to the ordinary method hitherto
employed of fermenting the leaf after thé rolling operation, which exposes the juices
to the direct influence of the atmosphere.
According to my herein described invention, the essential alterations or conversion
in the properties of the leaf, which its change of color from green to a suitable
degree of brownish autumnal tint indicates, is accomplished prior to the rolling

page_text: operation, and without the cells of the leaf having been previously burst, and the
juices thereby exposed to the direct influence of the atmosphere.
My improved process of manufacturing the green leaf into black tea is as
follows: The first operation to which I subject the leaf is one which accomplishes
its withering and "fermentation as one practically conjoint and simultaneous
process, whereby the requisite changes in the properties of the leaf and juices for
the production of a superior quality of black tea, are effected prior to the rolling
operation, Consequently what has hitherto in the ordinary method of manufacture
been carried out as two distinct operations or processes, namely the first and third
in the series of operations hereinbefore described, with the rolling process intervening
as the second operation, I now accomplish conjointly and more efficiently in one,
and as the first process, by subjecting the leaf at the outset of its manufacture to
the action of warm moist air in which a suitable supply of oxygen is maintained,
while at same time the leaf is continuously kept in motion by being lifted up
and then allowed to fall. This operation I preferably effect by placing the green
leaf in a revolving drum or cylinder through which a re-circulating current of warm
moist air is kept up together with a sufficient supply of fresh air, the drum being
fitted with a series of internal shelves which as the drum revolves successively lift
up the leaf and then allow it to drop to the bottom of the drum. A suitable
apparatus for this purpose is described in the Specification of previous Letters
Patent granted to me and dated 18 November 1895, No. 21905, when the same is
provided with means for introducing a sufficient quantity of fresh air to a
re-circulating current of moist warm air in place of an equal volume of discharged
air from which the oxygen has been more or less absorbed by the leaf.
During this combined withering and fermenting operation I preferably employ an
initial temperature of the air current circulating through the leaf of about 140° F.,
at which temperature a period of about an hour and a half is usually sufficient to
effect the desired results.
If a lower temperature be employed, the operation will require a longer time, and
if a higher temperature a shorter period, but in practice I usually work at the above
mentioned temperature of 140° F. in order to combine speed of manufacture with
efficiency of results. Too high a temperature, while shortening the time necessary
to merely limp or wither the leaf, would prevent its changing color from green to
the required brownish autumnal tint; but at 140° F. the change takes place
satisfactorily, together with the development of a pleasing aroma, and is a safe
temperature to employ. The time necessary for the completion of the process
cannot however be defined more than approximately, as it depends on the condition
of the leaf at the time, and on the weight being treated relatively to the volume of
moist warm air passing through or amongst same, and also on the general
characteristics of the finished tea which it may be desired to produce,-more or less
darkness of liquor, flavour &c. involving more or less modification in the detail
working of the process. The effects of the operation or process to which the leaf
is subjected in the drum are that it gradually gets bruised, and the juices and other
constituents of the cells become slightly rubbed up and mixed together therein, but
they do not perceptibly exude upon the surfaces of the leaf, which surfaces therefore
protect the juices from coming directly into contact with the air, and the color of
the leaf gradually changes from green to a greenish brown or a somewhat autumnal
coppery tint. In order to fully and satisfactorily accomplish this change of color, I
maintain a sufficient supply of oxygen in the circulating current of warm moist air
by exhausting or cutting out continuously or intermittently a portion of the
air current returning from the drum, and introducing an equivalent volume of fresh air
to it, as it is the conjoint operation of oxygen, moisture and heat which accomplishes
the required change in the properties of the leaf when it is manipulated in
this way.
The withered leaf, which in this operation parts with only a very small percentage
of its moisture, is then rolled in order to burst the cells and thoroughly complete
the admixture of the juices and other constituents of the leaf; after which the leaf

page_text: may be finally dried or desiccated, whereby a superior quality of black tea is obtained.
But I preferably adopt an alternative method of completing the manufacture of the
leaf. According to this alternative method I thicken or concentrate the juices
immediately after the rolling operation above mentioned by the evaporation.
therefrom of about 10 to 20 per cent of the contained moisture. This can be
effected by submitting the rolled leaf to a current of cool or warm dry air, for which
purpose the apparatus described in the Specification of Letters Patent granted to me.
and dated 21 April 1891 No. 6872, is suitable. After this the leaf may.receive a
second rolling to produce a closer and better curl or twist in the finished tea. It.
is then finally dried or desiccated.
It will be seen that in my process of manufacture of black tea as above described
in either of its modifications, the hitherto ordinary process of fermenting or
oxidizing the leaf subsequently to its being rolled and the cells thereby burst and
the juices themselves exposed to the direct action of the air, can thus be entirely
obviated, and I have ascertained that the resulting black tea obtained by my
herein described process of manufacture is a more valuable product; but the entire
elimination of the ordinary fermentation process after the leaf has been rolled, is not
an essential feature of my invention, as when desired for any special development
of quality in the tea to suit particular trade requirements the ordinary fermentation
may be more or less employed optionally. Nevertheless by mny herein described
improved method of manufacture, fermentation after rolling is no longer an
essential part of the manufacture of black tea as has hitherto been the case.
Dated this 15th day of January 1897,
J. C. MEWBURN & ELLIS,
55 and 56 Chancery Lane, London, Chartered Patent Agents.
Improvements in the Manufacture of Black Tea from the Green
Tea Leaf.
I, SAMUEL CLELAND DAVIDSON of Sirocco Engineering Works, Belfast, Ireland,
Merchant, do hereby declare the nature of this invention and in what manner the
ɛame is to be performed, to be particularly described and ascertained in and by the
following statement:―
According to the ordinary method of manufacturing black tea from green tea
leaf, the green leaf is first "withered" (as it is technically termed in Tea Factories) or
limped by being spread on mats or racks of trays and subjected thereon or in some
other suitable way to the action of the sun or to currents of cold or warm dry air.
During this operation the leaf usually parts with from about 25 to 50 per cent of its
moisture and it feels soft and flaccid when a mass of it is grasped in the hand. The
leaf when thus withered is then rolled, as the second stage in its manufacture, this
rolling bursts the cells, so that the juices exude over the surface of the leaf, and
render it a wet or moist mass.
This moist mass of rolled leaf is then as the third distinctive stage of its
manufacture spread in layers aud left so as to be more or less exposed to the
atmosphere, to undergo what is ordinarily termed "fermentation," and which
generally takes from two to four hours to accomplish, according to weather and
atmospheric conditions. During this operation the leaf changes from green to a
brownish or a copper color. Finally, after being then usually subjected to a second
rolling, the, leaf is dried, and during this operation it turns black, the resulting
product being what is known as "black tea."

page_text: . During the above described process of fermentation which the leaf undergoes after
it has been rolled and the cells burst so that the juices exude over the surface
of the leaf, the juices are consequently in more or less direct contact with the
atmosphere, and under these circumstances absorb oxygen therefrom with avidity,
the effect of which is that the tannin and other properties thereof rapidly undergo
changes, some of which have a deteriorating effect on the resulting product
of black tea.:**
It is however an essential part of the manufacture of black tea that some of the
alterations in the properties of the leaf which are indicated by its changing color as
above described, from its originally bright green to a more or less brownish hue,
before being dried, should take place, and I have now ascertained as the outcome of a
long series of experiments extending over inany years in various modifications and
methods of withering and fermenting tea leaf, that a better product of black tea is
obtained when this change of color is more or less effected in the leaf while the cells
are still unburst (i.e. prior to the rolling process) and when their contained juioes
are consequently to a considerable extent protected from the oxidising influences
of the atmosphere by the unbroken (though it may be bruised) cell tissue and
parenchyma of the leaf in the contradistinction to the ordinary method hitherto
employed of fermenting the leaf after the rolling operation, which exposes the juices
to the direct-influence of the atmosphere.
According to iny herein described invention the essential alterations or conversion
in the properties of the leaf, which its change of color from green to a suitable degree
of more or less brownish autumnal tint indicates is sufficiently accomplished prior to
the rolling operation and without the cells of the leaf having been previously burst
and the juices thereby exposed to the direct influence of the atmosphere, to so start
the changing of color in the leaf that during the subsequent process of rolling, the
requisite and coinplete change of color is accomplished through the whole mass
of the leaf, without its being subjected to the ordinary process of ferimenting in
layers subsequently to the rolling process for several hours as has hitherto been
necessary.
My improved process of manufacturing the green leaf into black tea is as follows:-
The first operation to which I subject the leaf is one which accomplishes its withering
simultaneously with a partial "fermentation" as practically one process, whereby the
requisite changes in the properties of the leaf and juices for the production of a
superior quality of black tea, are so set up prior to the rolling operation that the
completion of the fermentation process is accomplished during the subsequent rolling
of the leaf, without the leaf having to be put in layers for several hours, to ferment
as has been a necessary process in the hitherto ordinary method of manufacture of
the leaf. Consequently what has hitherto in the ordinary method of manufacture
been carried out as two distinct operations or processes, namely the first and third in
the series of operations hereinbefore described with the rolling process intervening
as the second operation, I now so far accomplish in one, and as the first process by
subjecting the leaf at the outset of its manufacture to the action of warm moist air
in which a suitable supply of oxygen is maintained while at same time the leaf is
continuously kept in motion by being lifted up and then allowed to fall that the
complete fermentation of the leaf is reached during the second or rolling process
without the employment of the herein before referred to third and separate process
of fermentation. The operation is preferably effected by placing the green leaf in a
revolving drum or cylinder through which a recirculating current of warm moist air
is kept up together with a sufficient supply of fresh air, the drum being fitted with
a series of internal, shelves which as the drum revolves successively lift up the leaf
and then allow it to drop to the bottom of the drum. A suitable apparatus for this
purpose is described in the Specification of previous Letters Patent granted to me and
dated 18th November 1895 No. 21905, when the same is provided with means for
introducing a sufficient quantity of fresh air to a recirculating current of moist warm
air in place of an equal volume of discharged air from which the oxygen has been
more or less absorbed by the leaf.

page_text: During this combined withering and partial fermenting operation I preferably employ
an initial temperature of the air current circulating through the leaf, of about 135 to
145° Fahr., at which temperature a period varying according to circumstances from
about an hour to an hour and a half is usually sufficient to effect the desired results.
5 If a lower temperature be employed the operation will require a longer time, and
if a higher temperature a shorter period, but in practice I usually work at a
temperature of 135° to 145° F. in order to combine speed of manufacture with
efficiency of results. Too high a temperature while shortening the time necessary to
merely limp or wither the leaf, would prevent its changing color from green to the
required brownish autumnal tint, but up to 145° F. the change takes place
satisfactorily together with the development of a pleasing aroma, and is a safe range
of temperature to employ. The time necessary for the completion of the process
cannot however, be defined more than approximately, as it depends on the condition
of the leaf at the time and on the weight being treated relatively to the volume
5 of moist warm air passing through or amongst same, and also on the general
characteristics of the finished tea which it may be desired to produce:―more or less
darkness of liquor, flavour, &c., involving more or less modification in the detail
working of the process. The effects of the operation or process to which the leaf is
subjected in the drum, are that it gradually gets bruised and the juices and other
constituents of the cells slightly rubbed up and mixed together therein, but they do
not perceptibly exude upon the surfaces of the leaf, which surfaces therefore protect
the juices from coming directly into contact with the air, and the color of the leaf
gradually changes from green to a more or less greenish brown or a somewhat
autumnal coppery tint; in order to accomplish to the requisite extent this change
of color, I maintain a limited supply of fresh oxygen in the circulating current of
warm moist air by exhausting or cutting out continuously or intermittently a portion
of the air current returning from the drum and introducing an equivalent volume
of fresh air to it, as it is the conjoint operation of oxygen moisture and heat while
the leaf is kept in motion which accomplishes the required change in the properties
of the leaf when it is manipulated in this way.
The withered leaf which in this operation parts with only a very small percentage
of its moisture, is then rolled in order to burst the cells and thoroughly complete the
admixture of the juices and other constituents of the leaf and during which process
the change of color set up in the first process proceeds further and is completed to
the required extent, after which the manufacture of the leaf may be completed by
finally drying or desiccating it, whereby a superior quality of black tea is obtained.
But I may also further preferably adopt an alternative method of completing the
manufacture of the leaf. According to this alternative method I thicken or
concentrate the juices immediately after the rolling operation above mentioned by
the evaporation therefrom of about 10 or 20 per cent of the contained moisture.
This can be effected by submitting the rolled leaf to a current of cool or warm dry
air for which purpose the leaf can either be again returned to the drum and a larger
supply of fresh air admitted into the circulating current than in the first employment
of the machine; or the apparatus described in the Specification of Letters Patent
granted to me and dated 21st April 1891 No. 6872, may be employed for this purpose.
After this the leaf may receive a second rolling to produce a closer and better curl
or twist in the finished tea. It is then finally dried or desiccated.
It will be seen that in my process of manufacture of black tea as above described
in either of its modifications, the hitherto ordinary process of fermenting or oxidizing
the leaf by putting it for a considerable time in layers subsequently to its being
rolled and the cells thereby burst and the juices themselves exposed to the direct
action of the air can thus be entirely obviated, and I have ascertained that the
resulting black tea obtained by my herein described process of manufacture is a
more valuable product, but the entire elimination of the ordinary fermentation
process after the leaf has been rolled is not an essential feature of my invention, as
when desired for any special development of quality in the tea to suit particular
trade requirements, the ordinary fermentation may additionally and optionally be

page_text: more or less employed. Nevertheless by my hereindescribed improved method of
manufacture such additional fermentation by putting the leaf in heaps or layers for a
period after rolling is optional and no longer an essential part of the manufacture
of black tea as has hitherto been the case..
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
The process hereinbefore described of manufacturing black tea from the green tea
leaf which process consists in first withering and at the same time more or less
oxidizing (or "fermenting" as it is technically termed) the green leaf as one combined
operation by submitting the unrolled leaf while it is being continually lifted up and
then allowed to fall to the action of a recirculating current of warm moist air with a
proportion of fresh air introduced continuously or intermittently in place of an equal
volume of discharged air from which the oxygen has been more or less absorbed by
the leaf, in then rolling the leaf and in then either finally drying it, or first thickening
the juices and then (with or without an intervening second rolling) finally drying it;
it being optional but not preferred to also submit the leaf to more or less of the
hitherto ordinary fermentation process before the final drying, all substantially as
as herein before described.
J. C. MEWBURN & ELLIS,
55 and 56 Chancery Lane, London, Chartered Patent Agents.