Black tea is the second largest category of teas in China and the most widely sold type of tea worldwide. The origin of black tea can be traced back to China, where it was first produced over 400 years ago during the Ming Dynasty by tea farmers in Wuyi Mountain, Fujian Province, as Zheng Shan Xiao Zhong.
In terms of processing techniques, due to differences in rolling methods and fresh leaf varieties, black tea can be classified into: Gongfu Black Tea, Xiao Zhong Black Tea, and Broken Black Tea.
Xiao Zhong Black Tea is the oldest type of black tea, originally produced in Wuyi Mountain, and is also the progenitor of other black teas;
Gongfu Black Tea comes in many varieties, produced in different regions, such as Qimen Gongfu Black Tea mainly produced in Qimen County, Anhui Province, and Dian Hong Gongfu from Yunnan Province;
Broken Black Tea is produced across a wide range of areas and is primarily for export.
Although there are different classifications of black tea, the basic process generally includes “withering, rolling, fermentation, and drying.”
As a fully fermented tea, the core and soul of black tea is its “fermentation,” which is a critical step in shaping its quality.
During this process, polyphenols in the tea oxidize, transforming the greenish aroma into a sweet fruity fragrance.
This step is crucial for developing the distinctive color, aroma, and flavor of black tea, as proper fermentation leads to the formation of more theaflavins and thearubigins, enhancing both taste and aroma.
Fermentation is a continuous process, not just a single step, occurring from rolling until drying. Typically, a dedicated fermentation step is set between rolling and drying to achieve optimal results.
For fermentation, the rolled tea leaves are placed in fermentation trays or carts, then put into fermentation chambers or rooms. In recent years, new types of fermentation equipment have been developed. Fermentation requires suitable temperature, humidity, and oxygen levels for the oxidation-polymerization reactions of tea polyphenols.
01
Temperature
Generally, the room temperature is controlled around 20-25°C, with the leaf temperature kept at about 30°C during fermentation. If the leaf temperature exceeds 40°C, the leaves need to be turned to dissipate heat to avoid excessive fermentation, which can result in low aroma and flavor, as well as a dark appearance. Especially during high-temperature seasons, cooling measures should be taken, and the leaves should be spread thinly to help dissipate heat; conversely, when temperatures are lower, the leaves should be spread thicker, and insulation measures may be necessary if needed.
02
Humidity
Maintaining an air humidity above 90% is beneficial for increasing the activity of polyphenol oxidase, promoting the formation and accumulation of theaflavins. Conversely, if the air humidity during fermentation is too low, it is detrimental to the enzymatic oxidation of tea polyphenols, causing non-enzymatic oxidation to intensify, resulting in a darker infusion and dull taste.
03
Leaf Spreading Thickness
Generally, the thickness should be between 8-12 cm. For tender leaves and smaller leaf types, spread them thinly; for older leaves and larger leaf types, spread them thicker. When the temperature is low, spread the leaves thicker; when the temperature is high, spread them thinner. Regardless of whether spreading is thick or thin, ensure good air circulation during fermentation. The leaves should be turned once during the process to facilitate heat dissipation and air circulation.
Black tea has a sweet and warm nature, is nutritionally rich, and has the effect of generating warmth and comforting the abdomen, as well as providing resistance to cold. After fermentation, the stimulating effects of black tea are significantly reduced, making it suitable for warming and protecting the stomach.
Tea Encyclopedia | Fermentation, a Unique Process of Black Tea
Fermentation in Black Tea
Process Principle
The fermentation of black tea is essentially the artificial acceleration of the oxidation of tea polyphenols.
The detailed reaction is as follows:
Tea polyphenols + polyphenol oxidase = (with oxygen participation) = pigments such as carotenoids, xanthophylls, and chlorophylls.
Suitable Enzyme Environment
The activity of polyphenol oxidase is influenced by the following factors:
Cell damage rate | Temperature | Humidity | Oxygen content
Influencing Factors
Artificially accelerating fermentation involves adjusting these variables to achieve an optimal state:
Rolling: Higher cell damage rates lead to greater surface area for fermentation
Constant Temperature: The fermentation room temperature is generally 20-30°C
Humidification: The fermentation room humidity is usually above 90%
Ventilation: Spread the leaves to a thickness of 10-15 cm and use exhaust fans
Cold Mixture Formation
Black tea containing 1.25% caffeine will exhibit the “cold mixture” phenomenon. Poor-quality black tea that is under-fermented and lacks sufficient theaflavin conversion will not produce this effect.