Cleaning processes that help in the production of tea varieties comprise
of three stages: cleaning after plucking, during manufacturing and
during packaging. Tea manufacturing involves different stages like green
leaf intake, withering, rolling, oxidation (fermentation), drying,
sifting/grading/cleaning of grades, packing and dispatch. Besides these,
moisture and temperature control also needs to be taken into
consideration in the context of tea leaves, dust and bacterial
contamination. When the leaf brought from the field is dry, there is
little increase in bacterial growth. But if the leaf brought to the
factory is wet, as it happens during the rains, the conditions become
favourable for bacterial growth. The food material required for
bacterial growth is drawn from the leaf itself. The bacterial growth is
checked with the removal of surface moisture.
Microbial Contamination
Tea leaf in the field carries on its
surface a large population of naturally occurring bacteria. So when the
leaf is carried to the factory, a considerable number of bacteria are
likely to be carried along with it. These bacteria under favourable
conditions develop very rapidly. The long interval of 16 to 18 hours
between plucking & processing followed by oxidation periods of about
1.5 hours for cutting, tearing and curling (CTC) and around 2.5 hours
for manufacture allow the possibility of a considerable bacterial
build-up. During firing, all the bacteria are destroyed, but moulds have
been known to persist even after drying.
Sources of Microbial Contamination
The
possible sources of contamination of tea include the oxidized leaf,
factory floor and air. The factory floor up to the stage of fermentation
can be kept clean by washing properly, but the same thing cannot be
followed in the drying room and beyond. If the drying and sorting rooms
are not washed or if the atmosphere is warmer and dusty, then a
different group of moulds start growing. These microbes affect adversely
the tea quality. Warm, dusty atmosphere and moisture along with the
changed substrate in the made tea provide ideal conditions for growth of
the moulds.
Talking about hygiene in the manufacturing process,
Dr Mohan Kumar, Director, UPASI Tea
Research Foundation, Tea Research Institute, Valparai, Coimbatore says,
“The teas marketed in India have to pass Food Safety and Standards
Authority of India (FSSAI) specifications that include black tea quality
parameters and the amount of pesticides residues & heavy metals.”
Explaining the cleaning processes in
detail Suresh Jacob, Vice president, Plantations, AVT Ltd, said, “The
first stage of manual cleaning helps in removing only foreign bodies;
all the bacteria get killed in the subsequent stages of drying. At green
leaf stage, removal of foreign body like stones, leaves etc are done.
In sorting and grading, removal of iron fillings at various stages and
removal of stalk & fibre (tea fibre) are accomplished to have a
clean black tea.” Withering and fermentation, which are entirely
dependent on change in ambient weather condition need close supervision.
In order to ensure that withering takes place in a favourable setting,
cleaning of machineries is meticulously done.
Jacob goes on to explain the need for
manual cleaning and why no sophisticated machinery is required to aid
the cleaning of tea. “The bolder leaf grades are cleaned by a machine
called colour sorter to clean and remove the long fibre and the smaller
grades are cleaned through fibre extractors. The Wet processing area
rollers/ fermenting area have to be cleaned well after every day’s
manufacture – ideally with hot water to kill the bacteria.” In terms of
the latest machinery that is available,
Dr Kumar opines, “The cleaning of tea machinery and floor in tea factories is done using high pressure water jet.”
During rolling, there is an immediate
drop in the microbial population due to the antiseptic properties of
oxidised polyphenols. But during this process the leaf juice is
expressed which drips down to the floor with fragments of leaf and may
become a source of bacterial growth. The juice and the fragments of leaf
may also be found adhering to the roller caps, roller doors, ball
breakers, CTC machines etc. If not cleaned properly, this infection is
carried over to the following day. It is a common experience to see
plenty of leaf particles adhering to the inside cover of the CTC machine
for a long period if not properly attended to. This makes the leaf over
fermented and also provides the source for bacterial growth. Similar is
the case with the roller-doors where juice and fragmented leaf
particles may be the source of contamination.
The floor of the rolling room can be a
dangerous source of infection in the factory. The juice expressed on the
floor should be washed away immediately. The floor should have a steep
slope from the rear to the front of the rollers to facilitate washing
and removing the juice to the side drain. However, a rung trolley placed
under the rolling table is always preferred.
The use of all metal leaf trolleys
reduces the bacterial growth possibilities in this stage. But these are
to be kept thoroughly clean. Green leaf sifters can infect leaf with
bacteria very easily. A high-pressure hose is suitable for cleaning
these sifters. Although precaution may be taken during the daily
cleaning at the end of the day’s manufacture, the infection tends to
develop on sifters during the course of manufacture, as adequate
cleaning is not possible unless the whole of the leaf has been rolled.
It is, therefore, advisable to have more than one sifter so that one can
be cleaned when the other is in use.
Fermenting Room
When rolled leaf is spread on floor for oxidation, some juice adheres
to the surface and, if not cleaned, the accumulated juice becomes a
source of bacterial contamination. Rough cement surfaces, cracks and
crevices are the sources for bacterial growth. The porousness or the
roughness of the cement floor can be done away to a great extent with a
coat of epoxy resin paint that keeps the floor shining white to
facilitate proper cleaning. Glazed tiles, metal sheets etc. are also
used as juice collected over these can easily be cleaned.
On badly cleaned “fermenting” surface,
the bacterial effect may arise in two ways. Bacteria present in the film
of juice may penetrate the lower layers of the bed of leaf and produce a
direct infection. The second effect is due to the bacteria attacking
the juice deposits already present on the floor and the juice freshly
deposited with each bed on leaf. The fermenting room should be well
drained and cleaned with an abrasive and good detergent. The water used
for cleaning the fermenting floor should be clean and bacteria free.
Many of the present day factories use
Continuous Fermenting Machine for oxidation. One of the biggest problems
with these machines is to keep them hygienically clean. Whenever such
machines are used, extreme care should be taken to keep them clean.
In order to achieve this, Jacob
explains, “Dry cleaning of withering troughs and dry cleaning and
washing the orthodox rollers, rolling room floor and fermenting floor
with high pressure jet using organic cleaning agents are done. Drying
room, heater room and packing room are also dry cleaned with brooms and
vacuum cleaner.”
Drying and Packing
Teas emerging out of a drier usually
have a low microbial count as most of the bacteria are destroyed during
firing. It may appear that after drying, there will be lesser chances of
microbial contamination.
Quality Control, Testing and Accreditation
Quality is a major discriminating factor
that sets the different tea brands apart from one another. “Acquiring
quality green leaf, (raw material) is tough. The quality in the end
product is achieved through Good Agriculture Practices (GAP) and Good
Manufacturing Practices (GMP – HACCP ),” says Jacob.
Says Dr Kumar, “NABL accreditation is
given to Chemical and Calibration Laboratories for following the norms
as per the requirements of ISO 17025:2005. Manufacturing aspects are
covered by HACCP (Hazard Analysis and Critical Control Points)
principles. Tea manufacturing units obtain ISO 22000 certification
besides GMP, which deals with the HACCP principles apart from quality
management system.”
Moreover, the pesticide residue facility
of UPASI Tea Research Foundation has been granted GLP certification by
National GLP Monitoring Authority of India. The testing facilities,
chemical laboratories at UPASI Tea Research Foundation, Tea Research
Institute, Valparai, Regional Centre, Conoor and Regional Centre,
Vandiperiyar are accredited by National Accreditation Board for Testing
and Calibration Laboratories, Government of India as per the
requirements of ISO 17025: 2005. Armed with adequate infrastructure,
UPASI TRF is also authorised to analyse the tea samples that are
intended for export and import.
Dr Kumar gives us an overall picture on
UPASI’s activities to encourage good manufacturing practices. “The Tea
Technology Division of UPASI TRF is engaged in research in terms of
manufacture, bio-chemical and quality aspects besides the testing
activities pertaining to the bio-chemical and quality parameters of
processed tea. Sometimes samples for NABL-GLP and FSSI certification too
reach us. We serve as a link between the plantations. In addition UPASI
Krishi Vikas Kendra (KVK) is working at Conoor to extend the analytical
and extension services for small tea growers, government farms and
tribal co-operatives. Members who have subscribed for our services and
those from KVK approach us.”
UPASI has developed the microbial
detection kit for testing the microbial contamination level in the tea
manufacturing unit. “In case of microbial contamination, cleaning agent
such as Purfue is being used to clean the machinery followed by high
pressure water cleaning.” AVT Ltd trains its cleaning personnel before
taking them on job. “Shortage of workers is a major challenge faced in
plantations,” remarks Jacob.
Waste Management
Care
is taken to make the cleaning process eco-friendly. “Washed water is
let into three filtration tanks which have gravels, charcoal and sand.
The filtered water is let into tea field. The bio degradable waste is
put separately in a pit and later used as manure. Non biodegradable
materials like plastic are collected separately and sold to the approved
buyer. Only organic cleaning agents are used for cleaning machineries
and floor,” explains Jacob. In terms of the tea waste and its
feasibility Dr Kumar cites only one productive use. “Only 2% is allowed
as tea waste. It gets used for vermi-compost production. The methodology
for composting has been disseminated to tea industry by UPASI. In case
of low grade tea varieties, they are used to make instant teas.”
Vijayalakshmi Sridhar
(With inputs from various sources)
Tea manufacturing in India is an age old
industry that dates back to the 1800s. The major tea belt constitutes
the states of Assam, West Bengal, Tamilnadu and Kerala.
Each tea growing areas has its own
distinctive pests and diseases though several of them might have been
recorded from more than one region. Number of pests and diseases
associated with tea plants in an area depends on the length of time for
which it is cultivated in that area. More than one thousand species of
arthropod pests and nearly 400 pathogens are known to attack tea all
over the world, though only about 300 species of insects and mites and
58 pathogenic fungi are recorded from tea in India. Crop loss due to
pest and diseases varies between 15 and 20%. Magnitude of the losses is
bound to be higher today in view of the increased production and
productivity besides the variations in climatic conditions. Mites are
serious pests of tea and they damage the green tissues of leaves,
thereby reducing the photosynthetic efficiency resulting in yield
reduction. Infestation leads to discoloration of leaves. Most of the
species occupy the under surface of the leaves but a few prefer the
upper surface also.
Ludhiana, October 16
