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How tea is produced at the factoryUpdated 8 months ago

The Process

One of the main reasons why there are thousands of different teas is due to the variables in production. 

Each tea type uses a combination of various production steps and techniques, and then within each style, there are variations by country, region, village and individual tea maker. 

The permutations are endless!

However, there are some key steps that are shared amongst all tea types as well as  some that are completely unique. 

  • Picking (plucking the leaves)
  • Withering or Wilting (reducing water content and softening)
  • Oxidising (allowing leaves to undergo chemical reaction with oxygen)
  • Fixing (fixing the enzymes to prevent any further start oxidation)
  • Rolling (crushing leaf cells to allow tea juice to coat leaf surface)
  • Drying (locking in the flavour and ensuring it is safe for consumption) 


Picking

Tea Picking typically takes place 3 times per year around a ‘flush’. A flush is simply a new germination of leaves on the tea bush after a period of dormancy. The first flush is also referred to as the spring flush, which commences with the change in environmental conditions associated with the change in seasons. Some countries like Sri Lanka are able to produce tea year round, but have peak flavour seasons due to specific favourable climatic conditions occurring at the time. 

The reason for picking the leaves at the time of flushes is because this is when leaves are at their most complex and flavoursome. Once the leaves have reached full maturity, the longer that leaves remain unpicked on the trees the more dull and bitter in flavour the leaves will become. This is because the continued exposure of the leaves to sun will convert the polyphenols (savoury elements) in the tea leaves into catechins (bitter elements). This is why the older dark coloured tealeaves are no picked (left on the tree) and why in some countries (like Japan) the tea leaves are covered in shade to block sunlight for the last 20 or so days to enhance the savoury element (umami flavour) of the tea. 

The age (or generation) of the tea leaf in each flush will affect the flavour. The immature leaves and buds (which have light flavour and are high in polyphenols) are picked for white tea. The more mature leaves are picked for green and black tea. During picking, pickers will typically pick 2 leaves and a bud as these leaves tend to provide the right balance of flavour and complexity as well as offer sufficient yield to be commercially viable). This is also part of the difference between hand picked and machine harvest tea. With hand picked tea, experienced pickers will only pick the fully developed and flavoursome leaf. With machine-harvested tea, all of the leaves are clipped from the tops of the bushes causing less flavoursome tea (bitter or dull leaves and immature leaves) being added into the mix. Hand picked tea is almost always superior for this reason.


Withering

Withering is the first stage of tea production once it reaches the factory. The picked leaves are laid out in long wooden or concrete troughs with a mesh wire screen on the base. A large van is located at one end of the trough, which blows air from underneath the leaves through the wire mesh. Over a period of around 12-20 hours depending on the humidity and temperature of the environment, the leaf will begin to reduce in moisture content from approximately 80% moisture content at the time of picking (the leaf at this stage is very stiff and waxy) to 58 to 60% moisture content when the tea maker decides to end withering (Here the leaf will be softer and more pliable).

As the moisture is removed, the leaf will continue to become softer and eventually become quite easy to bruise, so care is taken during this process not to handle the leaf too often. However, the leaves are generally turned twice to ensure an even withering of the leaf. At certain times of the year there’s a lot of moisture content in the air, or its been raining and there’s a bit of water on the leaves, it might be necessary to use hot air for withering. That’s not desirable, that accelerated process evaporates desirable taste and flavour volatiles, which results in lower quality or less character in the leaf. 

It is possible to under-wither or over-wither the leaf; bother will have a negative impact on the character and flavour of the tea. If the tea is under withered then the leaf will remain staff and there will be insufficient friction to adequately roll the leaf that will in turn result in poor oxidisation. If the tea is over-withered, there will be a large percentage of dust and flavour and character may be lost. Well-withered tea allows for effective rolling, with a lot of the leaf being ruptured or twisted allowing for the release of the tea liquor form the vascular bundles contained within the leaf.


Oxidation

The liquor that is released from the leaves during rolling accelerates the activity of enzymes in the tea as part of a process called oxidisation. During a period of 1 hour and 45 minutes to 2.5 hours, the green tea leafs will be converted into black tea. Both green tea & black tea are from the same plant only the black tea has been oxidised. To produce green tea, steam (or in some cases a hot wok shaped pan), will be used before or immediately after rolling to kill off any enzymes and prevent the oxidisation from taking place. The process of oxidisation develops flavour in the tea leaf, and depending on the level of oxidisation different flavour characteristics will be obtained. Heavy oxidised teas tend to be stronger an more bitter with a darker colour infusion as more of the sugars and the structure of the leaves break down through the extended activity of the enzymes.


Rolling

After withering is rolling. During the rolling process the leaves are dropped into the rolling machines that rupture the cell structure of the leaf and break the leaf down into smaller fragments. As a result of this process, polyphenol oxidase is release from the cells of the leaves which is what converts green tea into black tea if the tea has not gone through a heat process called panning or “kill green”. At the end of the tea manufacturing process, tea that has been properly withered and rolled will be described as being wiry and well twisted, an effect caused when cells are broken across the whole length of leaf. Tea that has been well rolled will allow for a more complete oxidisation, resulting in more character and flavour. 

Tea that cannot be properly rolled will often be cut up with a rotorvane for use poorer quality tea bags. In this way the manufacturer is able to increase their yields and lower the average production cost of the tea. 


Drying

With drying, the wet dhools (oxidised leaf) is placed into the dryer. The hot air of the dryer (approximately 105 degrees Celsius) is passed through the leaves for approximately 20 minutes, although there are different methods of drying including multi-stage drying. The application of heat ends the oxidisation process. Once complete, the tea to delivered from the dryer at approximately 3-4% moisture content – it tea warm, dry, and hydroscopic. If dryers are set at a higher than ideal temperature to dry the tea at a faster rate, this may cause over firing (resulting in tea that tastes sour and lacks flavour and aroma). Under-firing can result from the temperature being set too low or where too much tea is put through the dryer (this results in the tea developing fermented off-tasting flavours). The tea once fired should be crisp (able to be snapped) and highly aromatic (with bright complex aroma).  

If there is considerable moisture in the environment the tea maker may do a process called gapping. This process requires the tea to be placed through the dryer again for a second time to remove any excess moisture content that would diminish the flavour and aroma of the tea. Interesting to note is that every 100kgs of fresh pick green leaves produces on average only 21 to 25kgs of finished dry black or green tea.


Grading

The next process after drying is grading. In this process the dried leaves are placed on vibrating tables to separate the leaves into consistent sizing. Because of the varying sized mesh screens, larger leaves are cleared away at the top, and the smaller leaf vibrates through to the bottom screens. Larger leaf grades have relatively less surface area, be less intense in flavour and offer more subtle complexity. The large leaves impart less dissolved solids for a given time period, than for finer grade tea. Finer grade tea has greater relative surface area, imparts more intensity and more dissolved solids into the water. Both long and short grade leaves can be preferred depending on the application, however long leafy grade tea is preferred when the consumer will drink the tea black (without milk).


Cupping

The cupping is used to taste the tea at the end of the manufacturing process to determine how well the tea was made, to identify manufacturing faults and to evaluate whether the full potential of the leaf has been realised in the manufacturing process.


Packaging

Once the tea is approved for quality and approved, the bulk tea sacks are then typically shipped away from the factory to packinghouses for down packing into smaller bags of loose leaf tea or into tea bags.



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