Curing of tea leaves

The common categories of commercial tea – white tea, green tea, Oolong tea and black tea - result from different picking and curing techniques and have nothing to do with plant variety.

The flavor of tea comes from the method of curing and the essential oils in the leaf. Its stimulating and refreshing qualities come from the small amount of theine, chemically the same as caffeine in coffee.

Curing is a process to controlled drying in which the nutrients remaining in the leaf from photosynthesis are used to support the declining life processes of the leaf.

About 78% of total tea consumed represents black tea, a popular drink in many western countries which contains mainly oxidized polyphenols, whereas approximately 20% is green tea, which is primarily consumed in China and Japan and contains mostly non-oxidized polyphenols, more particularly catechins.
Curing of tea leaves

Drying of tea leaves

Drying achieved by blowing hot air through tea leaves, arrests oxidation by inactivating enzymes, resulting in color enhancement and the final balance of tea aroma and reduces the moisture content of the leaves to less than 5%.

In Keemun black tea processing, the leaves are subjected to drying after fermentation at 110 °C– 120 °C for 10 – 15 min. The moisture will drop below 20%.

After spreading the first dried leaves, another drying is carried out at 70 °C – 90°C for 45 –60 min to moisture below 4%.

Drying is usually done by a drying machine such as the multi-band drier or fluid bed drier.

The temperature is sufficient to inactivate the polyphenol oxidases. The sap released during rolling and fermentation solidifies during drying on the fine little hair on the surface of the leaf.

During drying, aroma substances are formed and the coppery-red color is changed to black (hence ‘black tea’).

Following the drying the leaves are sorted and graded to yield a commercial product.
Drying of tea leaves 

Processing of Black and Green tea

Processing of Black and Green tea
Black and green teas result from different postharvest treatment. In the case of black teas, the freshly picked green leaves are spread out on mats and allowed to dry out slowly and wither after which they mechanically rolled to break up the cells and liberate any enzymes which may present.

The rolled leaves are then fermented for several hours, either in baskets or spread out under damp cloths. During this stage the colorless tea tannins are partially oxidized changing to a reddish-brown color and some essential oil is developed.

This process is stopped by subsequent hot-air drying (frying). The whole process determines the flavor, strength, smoothness and color of the resulting infusion and calls for skill and experience to achieve consistent result.

Green teas are not fermented. The freshly picked leaves are steamed which prevent fermentation and blackening during the final drying process. The tea tannins are in consequence, largely in their original state as no essential oil is developed unfermented teas lack the aromatic character of the fermented varieties.

Oolong teas have a half way character; the leaves are allowed to wither and partially ferment before being rapidly dried at a high temperature. This results in a tea having a fine fragrant character.
Processing of Black and Green tea