Quality Control in Sorting
Greying of Tea
Tea is valued in the market for its colour, strength, quality and briskness. In order to obtain fine tea with all the above desirable characteristics, quality must be inherent in the leaf when it is first brought to the factory. No such skill can produce good tea out of poor quality leaf. Again, poor manufacture can easily turn good leaf into bad tea. One defect which may occur in manufacture, is greyness or the loss of bloom. This accounts for significant decrease in quality of tea. However, before dealing with details of it, let us understand the terms 'bloom' and greyness'.
Bloom
The bloom what is sought in tea leaf is achieved through the development of a varnish-like film on its outside surface. Failure to produce proper bloom leads to dullness in made tea. The bloom can be damaged through faulty sorting.
Greyness
Grey is perhaps the most undesirable colour in dry leaf. Greyness is caused when the gummy or varnished surface of the leaf, which plays an important part in its liquoring properties, is abraded or rubbed off. Greyness is particularly likely to occur during sorting and may be caused by one of the following factors.
- Tea particles get caught in sagging meshes in the sorting machine and are abraded through the movement of the trays.
- Blunt knives in the cutter and some older types of machine break, rather than cut, the tea. This not only produces excess dust, but also causes greying. Fast running cutters too tend to cause greyness.
- Excessive handling of the product also creates greyness.
- The tea prepared for sorting should have a moisture content of between 3 and 5%. Moisture above 5% causes greyness.
- Over-sorting quickly causes greyness because of the continuous rubbing and striking action of the particles against the trays. A leaf varnish is easily removed in this manner.
- Tea leaf fed into a sorter from an incorrectly placed hopper is subject to striking action that also removes the outer varnish.
- Excessive rolling may also cause greyness.
