Maintaining Quality & Hygiene in Tea manufacturing

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)