Processing of tea leaves

Freshly picked leaves of Camellia Sinensis undergo one or more processing steps, which make up what is called the normal tea processing method: I. Withering – helps to make the leaves and buds green and fresh. The leaves are placed on racks in a large, heated room, or are simply left to air dry in the sunlight. Withering has a twofold effect. First, the starch in the leaf begins to turn into sugar. Then, after the moisture content drops by 50-80%, the leaf becomes soft and pliable, and can be rolled without breaking. Withering takes between 10-24 hours, or – for white tea – only 4-5 hours. For hundreds of years, workers have checked the progress of the withering process by hand: they would take a handful of leaves and squeeze them to see how hard or soft they felt in the hand. But today, more precise testing methods are available – near-IR analyzers measure moisture levels instantly and can take ten readings per second. The desired moisture level varies from one growing region to another and depends on the characteristics of the leaves. For example, tea masters in the Assam region of India prefer a gentle withering, with a moisture level of 65-75%. In Sri Lanka, tea masters prefer a severe withering (a drier leaf), with a moisture level of between 50 and 60%. Without withering, tea leaves produce a bitter, unpleasant taste. II. Rolling – after withering, the leaves are rolled using machines or by hand (less often). The purpose of the process is to crush the leaves, releasing and exposing the sap to oxygen to stimulate fermentation. In some tea processing factories, the rolled leaves are then sieved through screens of varying fineness to sort them by size. Larger fragments may be rolled a second or third time to be twisted and crushed enough for the next step. Rolling takes about two hours. III. Oxidation – This is the main stage of the processing process, as it is during this stage that the flavor and value of the tea are established. In addition, the oxidation (fermentation) stage plays the most important role in creating the different categories of tea. For example, black tea is fully oxidized, while green and white teas are not oxidized at all. The rolled leaves are placed on trays and spread out to a thickness of three to six centimeters, then left in a cool, humid space to oxidize for one to three hours. The chemical reactions occurring inside the leaf cause it to heat up. To obtain the best flavor, it is essential that the oxidation is stopped at the peak of the reaction. If temperatures rise too much, the leaves taste burnt; if temperatures drop too much, the fermentation process stops, resulting in a residual metallic taste. During oxidation, the color of the leaves changes from green to reddish. The flavor, taste, and color of the tea are now definitively determined. IV. Drying or desiccation – the oxidized leaves are dried with hot air in a large dryer or on a conveyor belt, at temperatures between 85-88°C. This step aims to quickly stop the oxidation process. The reddish leaves now change color to a characteristic dark brown or black. The drying interval is also crucial, as if the leaves retain too much moisture (more than 12%), they can mold. If allowed to dry too long (moisture below 2-3%), they produce a tea that tastes burnt or has no taste at all. V. Grading or sorting – dried tea leaves are separated into various categories, depending on the particle size. The four categories are: whole leaf, broken leaf, debris, and dust. In general, whole leaf (which includes the tender tops and buds) produces the highest quality tea, while debris and dust are usually used to make quick-brewed teas, most often used in tea bags.