AUTOMATIC CONTINUOUS WITHERING MACHINE
FIELD OF THE INVENTION
The invention relates in general to withering, which is processing of green tea leaves, and in
particular to an automatic continuous withering machine. The machine expedites withering
of tea leaves while reducing requirement of manpower, time and power requirement.
BACKGROUND AND PRIOR ART
Withering of fresh leaf is the first and an indispensable stage in black tea manufacturing
process. The process of withering involves partial removal of moisture from the fresh leaf
carried out in order to condition the leaf physically for subsequent processing. Besides,
some chemical changes also take place and these are independent of the physical process.
The process of withering involves:
1. Chemical Wither: The term is perhaps misleading as it does not involve addition of
chemicals to the leaf. Bio-chemical wither is a function of time and temperature and is
independent of physical wither or degree of wither, Some bio-chemical changes occur in
green leaf from the time of its removal from the plant. Teas made from leaf which has
not been stored for chemical wither are harsh, metallic and green.
2. Physical Wither: It means partial dehydration of green shoots, without causing any
damage or discoloration with the objective of effecting desired change in their physical
condition. The extent to which the wither is to be carried out will depend upon the
method of manufacture
During withering, which is the first stage of tea processing, freshly plucked tea shoots
containing about 70% to 83% moisture are partially dehydrated to a moisture content from
65% to 70%. Besides physical changes, chemical changes in the leaf also take place.

Withering conditions the leaf physically for the next step of processing namely leaf distortion
which is carried out in CTC machines in case CTC tea processing, or in conventional rollers
in case of orthodox processing. At the same time it is to be conditioned for fermentation.
The leaf must attain certain degree of wither before it is suitable to roll or take a twist.
Withering percentage is defined as the weight of 100 Kg fresh leaf at the end of withering
process. The state of withered leaf is expressed in withering percentage.
Quality of finished tea, power required for withering, manpower for loading and unloading of
tea leaves into the withering trough, enormous space requirement etc. are some of the
basic drawbacks faced by the tea industry worldwide.
Chemical wither takes between 14-20 hours and physical wither takes 8-12 hours. Both
are dependent on the amount of moisture present in freshly plucked tea leaves.
The harvest of plucked tea leaf whether under or over withered, is undesirable for producing
quality tea. At present, this is based on the subjective experience and judgment of
experienced tea professionals in charge of withering and hence imprecise in nature. It is
therefore clear from the above that there is need for a mechanical withering machine that
overcomes most of the above drawbacks.
The automatic continuous withering machine according to the present invention eliminates
these drawbacks of the prior art.
OBJECTS OF THE INVENTION
The primary object of the present invention is to provide an automatic continuous withering
machine.
Another object of the invention is to provide a withering machine which substantially
reduces electrical power required for withering.

Yet another object of the invention is to provide a withering machine which substantially
reduces manpower required for withering.
Another object of the invention is to provide a withering machine which substantially
reduces the time required for withering.
A further object of the invention is to provide a withering machine which improves
uniformity of the withering process and quality of tea.
SUMMARY OF THE INVENTION
Accordingly the present invention provides an automatic continuous withering machine for
tea leaves comprising at least one chemical withering unit integrally and operably connected
to a physical withering unit. The withering machine comprises at least one chemical
withering unit, said chemical withering unit having an endless perforated mesh belt,
enclosed between two side and bottom walls and is adapted to carry tea leaves gradually
from the feeding side to the discharge side, a cooler blower and duct arrangement operably
connected to said conveyor -for feeding cool air required for chemical withering of tea
leaves; a delivery conveyor, one of its end being connected to the discharge end of the said
perforated mesh belt for collecting the chemically withered tea, the other end of the
conveyor being connected to the feeding side of a physical withering unit; said physical
withering unit comprises an endless mesh belt being arranged in plurality of decks in a
temperature controlled elongated enclosure.
Preferably two chemical withering units are operably connected to one physical withering
unit.
Preferably, a feeding conveyor is disposed on the top of the feeding side of the endless
perforated mesh belt of the chemical withering units. A cooling blower is operably connected
to the said perforated mesh belt through ducting arrangement.

The chemical withering units are connected to one auxiliary delivery conveyor which in turn
is connected to the main delivery conveyor. This conveyor is connected to a hopper at the
top of the feeding side of the physical withering unit.
Preferably, the endless mesh belt of the physical withering unit is arranged in three tiers.
A plurality of forced draft fans located on one side of the enclosure of the physical withering
unit is operably connected to the mesh belt of the unit through pipe ducts at plurality of
locations.
In a preferred embodiment a pair of forced draft fans is provided for each of the three
layers of mesh belt.
The forced draft fans are connected to individual radiators.
Preferably, a heat recovery unit at top of the physical withering unit is disposed at the
exhaust of the unit, said heat recovery unit is adapted to retrieve and recycle substantial
heat loss during physical withering.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 is a perspective view of the automatic continuous withering machine according to
the invention.
Figure 2 is a perspective view of the chemical withering unit of the machine according to the
invention.
Figure 3 shows the endless perforated mesh conveyor of the chemical withering unit of the
machine of the invention.
Figure 4 shows the feeding conveyor of the chemical withering unit of the invention.

Figure 5 shows the main and auxiliary conveyors of the machine according to the invention.
Figure 6 shows the physical withering unit of the machine of the invention.
Figure 7 shows the forced draft fans of the physical withering unit.
DETAILED DESCRIPTION OF THE INVENTION
The invention will now be described in an exemplary embodiment of the invention as
depicted in the accompanying drawings. There can, however, be other embodiments of the
invention within the ambit of the same inventive concept, all of which are deemed covered
by the disclosure
The automatic continuous withering machine (1) of the invention comprises at least one
chemical withering unit (2) and a physical withering unit (3) operably connected
downstream to the said at least one chemical withering unit for complete withering of tea
leaves. In the preferred embodiment as shown in figure 1, there may be a plurality of
chemical withering units which may or may not be simultaneously operational.
As shown in figures 2 to 4, the chemical withering unit (2) essentially comprises an
elongated endless perforated mesh belt (7) within a top-open enclosure having two side
walls (5). The perforated mesh belt enables the air to percolate through the leaf bed. A
feeding conveyor (6) is located at the tea leaf feeding end of the unit and is positioned on
the top the said feeding end of the endless mesh belt. The feeding conveyor is physically
separated from the perforated mesh belt and is supported on the side walls of the enclosure
to ensure the conveyor and endless belt run independently without interfering with each
other. Plurality of even discharge doffers (8) are provided at the opposite delivery end of
the feeding end for consistent discharge of tea leaves. A main drive means (10) is provided
on the discharge side of the chemical withering unit (2) for primarily moving the mesh belt

in an endless fashion and for continuous operation. The feeding conveyor is also similarly
provided with a secondary drive means (not shown) or might be driven by the main drive
means with suitable mechanical or electrical arrangement. A large cooling blower (9) is
provided in the vicinity of one of the side walls of the enclosure. The blower (9) is positioned
substantially in the middle of the length of the enclosure and is adapted to supply cool air
through ducts at the predetermined areas near the mesh belt.
Green leaf sifters and conveyors (not shown in drawings) for carrying tea leaves from sifter
to feeding conveyor may also be provided at the feeding side of the chemical withering unit.
There is also a catwalk (11) on the side wall of chemical withering unit for convenient
monitoring and supervision of the process.
As shown in figure 5, a main delivery conveyor (12) is connected at the discharge end of the
chemical withering unit. The delivery conveyor is upwardly inclined, so as the discharge end
of the delivery conveyor is connected to the top of the feeding end of a physical withering
unit (3) of the withering machine through a hopper (15). There may be two separate
auxiliary delivery conveyors (13) operably connected to the two chemical units' delivery
sides, converging at the main delivery conveyor (12) and are adapted to discharge the
withered leaf load to the main delivery conveyor. Suitable mechanical or electro-mechanical
load delivery means (14) are provided at the junction of the auxiliary and main conveyors.
The physical withering unit (3) essentially consists of a moving endless mesh belt arranged
in levels or decks in an enclosed environment (21). In the preferred embodiment as shown
in figure 6, the endless belt moves in three decks or levels (16, 16', 16"). However, the
number of decks may be varied according to the requirement.
The chemically withered tea leaves are fed at the top of the physical withering unit through
a hopper (15) and carried by the endless belt. A spiral spreader (17) is provided near the
hopper and on the top of the endless belt for uniform spread of leaves thereon. Plurality of

forced draft fans (19) are provided at a distance away from the receiving side of the
mechanical unit. These forced draft fans are operably connected to individual radiators (not
shown) as well as to the different segments of the unit through suitable ducting. There are
individual hot air common ducts (18) located at the side of the enclosure (21) corresponding
to each level (16, 16', 16"). As shown on figure 7, there are six forced draft fans (19)
stacked on each other corresponding to 3 levels or decks. Therefore each level of the
endless belt is connected to a pair of forced draft fans. The hot air draft from these fans is
fed to the three decks (16, 16', 16") through three parallel pipe ducts (18) which are also
arranged in three corresponding decks, as shown in Fig. 6 .The ducts open at different
segments of the enclosure (21) along the length thereof. A heat recovery unit (20) is
integrally located on the top of the enclosure (21) and connected to the hot air exhausts
from different segments of the enclosure.
Freshly plucked tea shoots containing around 70%-83% moisture is partially dehydrated to
around 65% to 75% moisture content and fed into the chemical withering unit (2) of the
machine through the feeding conveyor (6). Suitable mechanical arrangement is made to
ensure an even spread and thickness of the green tea leaves on the feeding conveyor. The
smooth continuous motion of the feeding conveyor delivers the tea leaves on to the
perforated mesh belt (7) located just under the feeding conveyor. The perforated mesh belt
gradually moves on in a continuous and endless manner from the feeding to delivery side
and the tea leaves thereon are withered with the help of moisture and cool air supplied on
the perforated mesh belt bed by the cooling fan (9) located in the vicinity of the side wall
and through the ducts. It is to be understood that the speed of the perforated mesh belt is
controlled by the main drive (10) and is capable of varying the withering time depending on
moisture content and other physical parameters of the green tea leaves. The perforated
mesh belt is encased between two side walls (5), without a top wall or ceiling. This ensures
that the tea leaves on the belt are chemically withered with ambient humidity.

Chemically withered tea leaves are discharged on the respective auxiliary hoppers (13)
which in turn carry the chemically withered tea leaves to the primary conveyor (12) through
the load delivery means (14). The primary conveyor carries the chemically withered tea
leaves to the physical withering unit (3). The tea leaves are fed at the hopper located at the
top of the physical withering unit.
As discussed above, the physical withering unit (3) is a temperature and humidity controlled
enclosure in which a single moving mesh belt conveyor is arranged in tiers or decks. The tea
leaves from the hopper are evenly spread on the mesh belt by the spiral spreader (17).
Relative Humidity (RH) and temperature on each of the layers or a part thereof is
individually controlled by the forced draft fans (19) which are in turn connected to individual
radiators.
Humidity, temperature sensors are also provided on this unit for controlling and maintaining
the required parameters optimum for physical withering by evaporating the moisture.
To prevent any loss of energy, the exhaust hot air is recycled in a heat recovery unit (20)
provided on the top of the enclosure of the unit and connected to the hot air exhaust points.
The automatic continuous withering machine according to the present invention performs
the entire withering process involving both physical and chemical withering of the fresh tea
leaves.
The endless belt carries the tea leaves along the layers and delivers the physically withered
leaves at the discharge end for further processing of the tea leaves before it is ready for
consumption.
The automatic continuous withering machine according to the present invention ensures
huge reduction in total time required for withering by providing mechanised, automatic
uniform feeding and spreading of leaf. This also ensures consistent quality of withering,
always. The machine helps in achieving enormous savings in manpower and electrical power

required for withering. The integrated machine is easy to install and there is a massive
reduction in overall withering space required. The machine also improves the hygiene
substantially as the need for physical handling of tea leaves reduces. Different embodiments
of the machine offer flexibility to accommodate into various factory layouts.
The present invention has been described with the help of a preferred embodiment.
However it will be clear to a person skilled in the art that variations and modifications would
be possible without deviating from the concept of the disclosure and scope of the appended
claims.

We Claim:
1. An automatic continuous withering machine (1) for tea leaves comprising at least one
chemical withering unit (2) integrally and operably connected to a physical withering unit
(3).
2. The withering machine as claimed in claim 1, wherein said chemical withering unit (2)
comprises an endless perforated mesh belt (7) enclosed between two side and bottom walls
and is adapted to carry tea leaves gradually from the feeding side to the discharge side, a
cooler blower (9) and duct arrangement operably connected to said perforated mesh belt
(7) for feeding cool air required for chemical withering of tea leaves;
-a delivery conveyor (12) , one of its ends being connected to the discharge end of the said
perforated mesh belt for collecting the chemically withered tea and the other end of the
conveyor being connected to the feeding side of a physical withering unit (3); and
- said physical withering unit (3) comprises an endless mesh belt being arranged in plurality
of decks in a temperature controlled elongated enclosure (21).
3. The machine as claimed in claim 1 or 2, wherein two chemical withering units (2) are
operably connected to one physical withering unit (3).
4. The machine as claimed in claims 1 to 3, wherein said chemical withering unit (2) has a
feeding conveyor (6) disposed on the top of the feeding side of the endless perforated mesh
belt (7).
5. The machine as claimed in any preceding claim, wherein a cooling blower (9) is operably
connected to the said perforated mesh belt through ducting arrangement.

6. The machine as claimed in claim 3, wherein each chemical withering unit (2) is connected
to one auxiliary delivery conveyor (13), which in turn is connected to the main delivery
conveyor(12).
7. The machine as claimed in any preceding claim, wherein the main delivery conveyor (12)
is connected to a hopper (15) at the top of the feeding side of the physical withering unit
(3).
8. The machine as claimed in any preceding claim, wherein the endless mesh belt of the
physical withering unit is arranged in three layers (16, 16', 16").
9. The machine as claimed in any preceding claim, wherein a plurality of forced draft fans
(19) located at a side wall of the enclosure (21) of the said physical withering unit is
operably connected to the mesh belt of the unit through pipe ducts (18) at plurality of
locations.
10. The machine as claimed in claim 9, wherein a pair of said forced draft fans (19) is
provided for each of the three layers of mesh belt.
11. The machine as claimed in claim 9, wherein the said forced draft fans are connected to
individual radiators.
12. The machine as claimed in any preceding claim, wherein the a heat recovery unit (20)
located at top of the physical withering unit is connected to the hot air exhaust points and is
adapted to retrieve and recycle substantial hot exhaust air to prevent heat loss during
physical withering.

ABSTRACT

An automatic continuous withering machine (1) for tea leaves comprises at least one
chemical withering unit (2) connected to a physical withering unit (3). The chemical
withering unit (2) comprises an endless perforated mesh belt (7) adapted to carry tea
leaves gradually from the feeding side to the discharge side, a cooler blower (9) and duct
arrangement connected to said belt (7) for feeding cool air for chemical withering of tea, a
delivery conveyor (12), one end being connected to discharge end of belt (7) for collecting
chemically withered tea and other end connected to feeding side of a physical withering unit
(3) which comprises an endless mesh belt arranged in plurality of decks (16, 16', 16") in a
temperature controlled elongated enclosure (21). Forced draft fans (19) are located at a
side wall of the enclosure (21) and a heat recovery unit (20) is located on top.