Fermentation is a key process in the processing of black tea. After fermentation, the leaf color changes from green to red, forming the quality characteristics of red tea red leaf soup. The essence of black tea fermentation is that under the rolling action of leaves, the tissue structure of leaf cells is destroyed, the semi permeable vacuolar membrane is damaged, the permeability increases, and polyphenolic substances are fully contacted with oxidases, causing enzymatic reactions of polyphenolic compounds and producing a series of oxidation, polymerization, condensation and other reactions, forming colored substances such as theaflavins and thearubigins, while producing substances with special aromas.

The quality of black tea fermentation is related to factors such as temperature, humidity, oxygen supply, and duration of the fermentation process. Usually, the room temperature is controlled at around 20-25 ℃, and it is advisable to maintain the temperature of the fermented leaves at around 30 ℃. Maintaining air humidity above 90% is beneficial for enhancing the activity of polyphenol oxidase and facilitating the formation and accumulation of theaflavins. During fermentation, a large amount of oxygen is required, so it is important to maintain good ventilation and pay attention to heat dissipation and ventilation. The thickness of leaf spreading affects ventilation and leaf temperature. If the leaf spreading is too thick, poor ventilation will occur, and if the leaf spreading is too thin, the leaf temperature will not be easily retained. The thickness of leaf spreading is generally 10-20 cm, and young leaves and small leaf shapes should be spread thinly; Old leaves and large leaf shapes should be spread out thick. Spread thick when the temperature is low; When the temperature is high, it should be spread thinly. The length of fermentation time varies greatly depending on fermentation conditions, degree of rolling, leaf quality, tea variety, and production season, and should be based on moderate fermentation. The fermentation time of Mingyou Gongfu black tea is generally 2-3 hours

The degree of fermentation should adhere to the principle of “preferring light over heavy”, and the moderate standard is: the fermentation leaves lose their green and grassy aroma, have a distinct floral and fruity aroma, and the leaves turn red in color. The color depth of fermented leaves varies slightly with the season and the age and tenderness of fresh leaves. Generally, spring tea is yellow red, while summer tea is red yellow; The tender leaves have a uniform red color, while the old leaves are red with a hint of green. If the fermentation is insufficient, the aroma of the tea leaves will be impure, with a greenish tint. After brewing, the color of the soup will be reddish, the taste will be green and astringent, and the leaves will have green flowers at the bottom. If the fermentation is excessive, the tea leaves will have a low and dull aroma, and after brewing, the soup color will be red, dark, and cloudy, with a plain taste and red and dark leaves with many black strips at the bottom. If the aroma is sour, it indicates that fermentation has been excessive.

There are various fermentation methods for black tea, including natural fermentation, fermentation chamber, and fermentation machine. Natural fermentation is the most traditional fermentation method, which involves placing rolled leaves in bamboo baskets, covering them with a damp cloth, and placing them in a well ventilated indoor environment. The fermentation room is an independent space specifically set up in the tea processing workshop for the fermentation of black tea. Fermentation machines have developed rapidly and been widely used in recent years due to their ability to achieve temperature and humidity control during fermentation.

At present, fermentation machines are mainly composed of continuous fermentation machines and cabinet Tea fermentation machines.

The continuous fermentation machine has a basic structure similar to a chain plate dryer. The processed leaves are evenly spread on a hundred leaf plate for fermentation. The hundred leaf plate bed is driven by a continuously variable transmission and equipped with ventilation, humidification, and temperature adjustment devices. It is suitable for continuous automatic production lines of black tea.

Box type black Tea fermentation machines come in a wide variety of types, with a basic structure similar to baking and flavoring machines. They have stable temperature and humidity control, small footprint, and easy operation, making them suitable for various small and medium-sized tea processing enterprises.

The red tea visualization fermentation machine mainly solves the problems of difficult mixing, insufficient ventilation and oxygen supply, long fermentation cycle, and difficult observation of operating conditions in traditional fermentation equipment. It adopts a rotating stirring and flexible scraper structure, and has functions such as visible fermentation status, timed turning, automatic temperature and humidity control, and automatic feeding and discharging.

TIPS

Requirements for the establishment of fermentation rooms:

1. The fermentation chamber is mainly used for the fermentation operation of black tea after rolling, and the size should be appropriate. The area should be determined according to the production peak of the enterprise.
2. Doors and windows should be appropriately set up to facilitate ventilation and avoid direct sunlight.
3. It is best to have a cement floor with ditches around for easy flushing, and there should be no dead corners that are difficult to flush.
4. Indoor heating and humidification equipment should be installed to control the indoor temperature within the range of 25 ℃ to 45 ℃ and the relative humidity within the range of 75% to 98%.
5. Fermentation racks are installed inside the fermentation chamber, with 8-10 layers installed at intervals of 25 centimeters each. A movable fermentation tray is built in, with a height of about 12-15 centimeters.