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

Oolong tea, also known as green tea, is a semi fermented tea that can be processed using both the Minnan Oolong method and the Minnan Oolong method. The processing principle and method are basically the same, and the main process is fresh leaves withering, adjusting, greening (shaking and transportation), withering, rolling, and drying. During processing, the polyphenols in fresh leaves undergo partial oxidation, resulting in the unique quality and style of Xingniaolong tea – high aroma, mellow taste, and green leaf red border.

The formation of the quality of oolong tea comes from the utilization of fresh leaf raw materials and processing techniques.

1. Characteristics of Fresh Leaves in Various Varieties of Oolong Tea

Oolong tea has a particularly strong dependence on the germplasm characteristics of different varieties, and the varieties suitable for producing Oolong tea are generally mostly mid leaf varieties. The fresh leaves suitable for making oolong tea are mostly mature new shoots. Variety is the material basis for harvesting high-quality oolong tea. China has a wide variety of oolong tea varieties, including 10 national level varieties, 17 provincial-level varieties, rare varieties, and dozens of local varieties. There are mainly narcissus, Dahongpao, cinnamon, Tie Guanyin, Benshan Mao, Huangjin Gui, Meigu, Aijiao Wulong, Qilan, Buddha’s Hand, Daye Wulong, etc.

Different varieties of oolong tea have different biological characteristics and quality features. Anxi Tieguanyin Tea has the flavor of “phonology”; The population of narcissus varieties has a strong and smooth throat rhyme; The aroma of Wuyi cinnamon is like cinnamon; Anxi Golden Osmanthus has a fragrance like orchids, known as the “Heavenly Fragrance”. The rich variety resources of oolong tea make the characteristics of oolong tea products obvious. In addition, the traditional processing methods and rare single variety make the personality of oolong tea products more prominent. A few products cannot be replicated, making them appear very rare.

The picking standards for oolong tea are different from other types of tea. Generally, new shoots with small or medium openings are picked, and the picking standard is to pick 2-3 leaves from the bud. Fresh leaves that are too tender or too old are not suitable. The content of some major chemical components related to quality varies among new shoots of different maturity and leaves from different parts.

The pattern is that as new shoots grow and leaves mature, the content of ether extract, sugars, carotenoids, and flavonols gradually increases, while the content of tea polyphenols gradually decreases. The content of ether extract is positively correlated with tea aroma, and high content leads to high aroma. The content of carotenoids increases with the elongation and maturation of new shoots, and it is a type of substance that can be converted into high aroma components in tea production; Mature leaf tip cells contain increased chlorophyll, resulting in high photosynthetic efficiency. The content of large starch granules, sugars, and total pectin also increases, giving oolong tea soup a rich and mellow flavor; The relative content of polyphenols with astringency also decreases with the increase of new shoot maturity, especially ester catechins, which contribute to the formation of a rich and mellow taste in oolong tea.

This indicates that the newly harvested mature shoots are perfectly suited to the high aroma and mellow taste of oolong tea, and the chemical basis they possess meets the quality requirements of oolong tea.

Changes in Major Chemical Components in Oolong Tea Processing

(1) Changes in aroma chemical composition

The aroma substances of oolong tea are mainly composed of polyphenols, aromatic substances, sugars, pectin substances, and amino acids. The typical characteristic aroma of oolong tea is the natural orchid fragrance, which is composed of components such as linalool oxide, orange blossom tertiary alcohol, aromatic alcohol, phenylethanol, indole, jasmonic acid, jasmonic acid lactone, and methyl jasmonate.

The aroma of oolong tea is also related to theaflavins, thearubigins, and theaflavins. Within a certain range, thearubigins are positively correlated with both aroma and taste, and the addition of thearubigins and theaflavins is significantly positively correlated with aroma. The ether extract and aromatic substances of oolong tea are higher than those of red and green tea, which is an important reason for the formation of the special aroma of oolong tea.

(2) Changes in the chemical composition of taste

The chemical composition of taste is determined by the variety, the unique proportion of substances produced by different regions, and the transformation during processing. The characteristic taste of oolong tea is mellow and durable, mainly due to its rich content of substances and coordinated proportions.

Due to the fact that fresh leaves need to have a certain degree of maturity during harvesting, ether extracts are mostly in the static stage of greening, which promotes the transport of water and soluble substances from the stem to the leaf flesh cell tissue through the transport tissue, thereby increasing the content of effective ingredients in the leaves and providing a material basis for the strong flavor and foam resistance of oolong tea. In addition, the drying process fixes various water-soluble substances, which plays a role in enhancing soup color, improving taste richness, and promoting aroma maturation.

(3) Changes in the chemical composition of color

The appearance color of oolong tea is required to be sandy green and oily, the soup color is required to be golden, and the bottom of the leaves is required to have green leaves with red borders, which is closely related to the special processing methods of oolong tea.

The main components that make up the color of oolong tea are chlorophyll, carotenoids, and polyphenolic substances. These substances undergo changes during the manufacturing process, with a decrease in chlorophyll content, changes in the ratio of chlorophyll a and chlorophyll b, partial oxidation of polyphenolic substances, as well as an increase in theaflavins and thearubigins content and an increase in theaflavins during the later stages of drying, which determine the formation of the unique color of oolong tea.