How is the color, aroma, and shape of green tea formed

Biochemical principles underlying the formation of green tea quality

Green tea is the main type of tea in China. Due to different processing methods, it can be divided into stir fried green tea, steamed green tea, and stir fried green tea, which can be further divided into eyebrow tea, pearl tea, flat tea, needle tea, etc.
Although there are many types of green tea products and various processing methods, their basic processing principles are consistent. The basic principle of green tea processing is to use high temperature to kill the green leaves, destroy enzyme activity, inhibit the oxidation of polyphenolic compounds under enzymatic action, in order to avoid the production of red stems and leaves, and maintain the quality and characteristics of clear green leaves. At the same time, different processing techniques are used to develop aroma, improve taste, and enhance appearance, thus forming various styles and qualities of green tea categories.

The quality of green tea is composed of four factors: color, taste, aroma, and appearance of the tea leaves. There is a certain internal relationship between each factor, and their formation is the result of the joint action of various internal and external factors of the tea leaves, including fresh leaf raw materials (such as variety, cultivation conditions, picking standards, etc.), processing methods, processing environment, etc.

1.Formation of color

Tea color is divided into three parts: dry tea color, tea soup color, and leaf base color. The color of fresh leaves is basically green, and the main coloring substances in fresh leaves include chlorophyll, lutein, carotenoids, anthocyanins, and anthocyanins.

Chlorophyll, lutein, and carotenoids are fat soluble pigments that are insoluble in water, so their retention is related to the color of dry tea and leaf base. After being heated, a portion of chlorophyll is converted into magnesium free chlorophyll, which participates in the formation of the color of dry tea; A small portion will undergo hydrolysis and become hydrophilic, which will affect the color of the tea soup when it enters. Anthocyanins and anthocyanins are the main water-soluble pigments in fresh leaves, which are easily oxidized and turn into various oxidation products such as orange, red, and even brown, directly affecting the color of green tea.

During the processing of green tea, high-temperature sterilization is used to inhibit enzyme activity, ensuring the quality characteristics of the “three greens” of green tea. In addition, the formation of dry tea color is also related to the amount of fuzz on the surface of fresh leaves. The surface of tea leaves adhered to by fuzz during processing can directly affect the color of dry tea.

2.Formation of aroma

There are over 200 detected aromas in green tea, some of which are retained from fresh leaves, while the majority are formed during processing. The formation of green tea aroma mainly occurs through the following ways: emitting the original low boiling point green odor in fresh leaves, revealing a fragrant or floral aroma; The aromatic substances in fresh leaves are converted into aromatic substances during the processing.

The main substance that forms the aroma of green tea is aromatic oil. The content of aromatic oil in fresh leaves is very low, but its composition is complex, including acids, aldehydes, ketones, alcohols, alkenes, etc. Among them, Qingye alcohol, which has the highest content in fresh leaves, is a substance with a grassy and green odor. It can emit these green odors after withering and heating.

In addition, during the tea processing, some nitrogen-containing substances such as proteins and amino acids, carbon compounds such as sugars and fats, as well as some pigment substances such as carotenoids, undergo various reactions during heating and drying to form sweet, high fire, burnt, and other special aromas.

3.The formation of taste

The substances that form the taste of tea are water-soluble. There are polyphenols and their oxidation products, amino acids, caffeine, sugars, water-soluble pectin, organic acids, etc. Each substance has its own taste characteristics. Polyphenols are bitter and have strong astringency; Amino acid freshness; Sugar sweet alcohol; The bitterness of caffeine and tea saponin.
The components of various substances have their own taste characteristics. Polyphenols and their oxidation products are the basic components that determine the taste of tea, of which 70% are catechins. The taste of various catechins varies, with simple structures having strong astringency and being more delicious, while complex structures have a stronger astringency. The taste of green tea is the result of the combination, coordination, and comprehensive reaction of various components.

During the initial production process of green tea, protein hydrolysis can increase some amino acids, while polyphenol oxidation and precipitation decrease, resulting in a lower phenol ammonia ratio and a stronger and fresher tea flavor. During the initial production process, sugars also increase due to the hydrolysis of starch, which can counteract bitterness in taste and make the tea taste mellow.

4.Formation of appearance

The formation of green tea’s appearance is closely related to the quality of fresh leaves, such as tenderness, shape, and internode length of new shoots. Different processing techniques can also shape their own external characteristics.
After withering, leaves that are not rolled and twisted will maintain their natural shape when dried; After withering, the tea leaves are rolled, sun dried or dried to maintain the shape of the rolled leaves; After rolling and twisting the withered leaves, stir fry them dry or semi dry. During the stir frying process, different techniques or machinery are used to further shape the leaves based on the shape of the rolled leaves, such as eyebrow tea, pearl tea, Bi Luo Chun, Yu Hua tea, etc; The withered leaves are directly stir fried without rolling or twisting, and clever techniques are used to shape them during the frying process. For example, in the processing of flat and smooth high-grade Longjing tea and some stir fried Dong tea leaves, as the tenderness of the fresh leaves decreases, the content of effective ingredients decreases, resulting in famous teas. The shape gradually becomes coarse and loose.

Cellulose, hemicellulose, lignin, and pectin are the components of the fresh leaf cell wall and the supporting substances of the tea plant. During the process of new shoot propagation, as the fiber and other components of the leaves increase, the leaf texture appears coarse and hard, and the appearance of the produced hairy tea is often coarse and aged.