Black tea withering refers to the process in which the fresh leaves entering the plant will lose water for a period of time, so that certain hard and brittle stems and leaves are wilted and withered. Withering is not only a physical loss of water, but also a process of chemical changes of contained substances. It is the first process in the initial production of black tea, and it is also the basic process to form the quality of black tea.

The purpose of withering is to evaporate part of the water, reduce the tension of the tea cells, make the leaf stalks become brittle and soft, increase the toughness of the buds and leaves, and make it easy to twist into strips; the second is to cause the inner part of the tea tips due to the loss of water. A series of chemical changes containing substances lay the foundation for material changes to form the specific quality of black tea color and fragrance.

Outdoor sunlight withers：

Indoor natural withering is to spread fresh leaves on a withering rack for withering. Each withering rack is divided into 8-12 layers, each layer is about 20 cm apart, and each layer is laid with a withering curtain woven from bamboo. The area of the curtain is generally 1.5 square meters, and 0.5-0.6 kg of leaves per square meter are required. The withering process should be checked frequently, and the uniformity of withering should be paid attention to in time. Generally, the temperature of the upper and lower layers is different. The upper curtain is 1-2℃ high. The curtain frame with better ventilation at the doors and windows loses water faster, so it should be spread thickly. Open windows and doors in time on sunny days to speed up the withering rate, and close doors and windows properly on cloudy and rainy days to maintain indoor temperature. The time of withering varies greatly due to the season, the age of the leaves and the weather. Spring tea is sunny, fresh leaves of grade 1-2 can be withered in 15-20 hours, and sometimes it can be delayed to 36-48 hours in rainy days. Therefore, the indoor natural withering is difficult to adapt to the mechanized tea making today. In the early 1960s, indoor natural withering was gradually eliminated and withering troughs were used.

Withering by withering trough:

Withering trough withering is a method in which fresh leaves are placed in a ventilating trough and heated with air to accelerate the withering process. The withering trough is composed of two parts: trough body and ventilation equipment. Generally, the trough is 10 meters long, 11.5 meters wide, and 80 cm high. The bottom of the trough has a uniform temperature slope and heating blast equipment. The trough surface has iron or The leaf curtain (box) woven from bamboo can spread 2-2.5 kg of leaves per square meter, and the thickness of the spread leaves is about 20 cm. The hot (or cool) wind is sent down to accelerate the evaporation of water. It is rainy in spring and needs to be warmed and withered, but the general temperature should not exceed 30℃, and the withering time is generally 6-12 hours. In summer, the temperature is relatively high, the air is relatively dry, and cold wind is sufficient. This withering method can save plant area, labor and reduce labor intensity, and can better control the process of withering. The quality of withered leaves is better, and it is the method commonly used in my country.