How is the color, aroma, and shape of black tea formed
Black tea includes Gongfu black tea, broken red tea, and small variety black tea. Their production methods are generally the same, with four processes: rolling (cutting), fermentation, and drying. Gongfu black tea, broken red tea, and small variety black tea are fully fermented fresh leaves that undergo a series of physical and chemical changes in the chemical composition of the leaves through processes such as withering, rolling (cutting), fermentation, and drying, forming the unique quality characteristics of black tea.
Black tea increases enzyme activity through withering, and then undergoes a series of biochemical changes centered on the enzymatic oxidation of tea polyphenols through rolling and fermentation, ultimately forming the quality characteristics of red tea leaves.
After fresh leaves are detached, the activity of polyphenol oxidase gradually increases as the dehydration process progresses; The activity of polyphenol oxidase in wilted leaves is 2-4 times higher than that in fresh leaves. After rolling, wilted leaves greatly accelerate the rate of oxidase oxygen, and enzymatic oxidation becomes the mainstream biochemical change during the rolling stage. As the fermentation process progresses, enzyme activity gradually decreases until the drying operation begins. When the leaf temperature reaches 70 ℃, polyphenol oxidase completely denatures and loses its activity.
1. Formation and transformation of black tea pigments
The main substances of tea polyphenols are catechins. Catechins exist in the vacuoles of fresh leaf cells, while polyphenol oxidase mainly exists in chloroplasts and mitochondria in the cytoplasm. But when the leaf tissue is damaged, such as rolled or cut, catechins come into contact with polyphenol oxidase, and under oxygen conditions, catechins rapidly undergo enzymatic oxidation, first producing catechin quinone.
The quinone substance quickly undergoes polymerization again, gradually producing theaflavins. Further oxidation of theaflavins results in the production of thearubigins, which undergo further oxidation and polymerization with amino acids and other substances, ultimately forming theaflavins. Theaflavins and thearubigins are the main substances that form the red leaf soup of black tea.
The entire process of catechin oxidation and polymerization to form theaflavins gradually deepens the color of the substance. Quinone is yellow, and theaflavins are orange yellow. Tea red pigment is red, while tea brown pigment is dark brown. The decomposition and destruction of chlorophyll during the production process of black tea is significant. The decomposition and destruction of chlorophyll are caused by enzymatic or non enzymatic hydrolysis, as well as the magnesium removal during heating, resulting in the formation of black brown color in red tea.
2. Formation of black tea flavor
The main chemical components that form the taste of black tea include polyphenolic compounds, caffeine, carbohydrates, amino acids, and other substances.
Polyphenols are the main components that make up the strong flavor of black tea. Among them, theaflavins have strong astringency, while thearubigins have a mellow taste. The rich content and moderate proportion of the two (thearubigins: theaflavins=1015) are the main reasons for the formation of high-quality black tea flavor.
The main components that make tea soup fresh and refreshing are amino acids, unoxidized catechins, theaflavins, and caffeine. Amino acids are substances with a savory taste. During the production process of black tea, various free amino acids are formed after protein hydrolysis, which coordinate with polyphenolic compounds to give black tea a rich and refreshing taste. Caffeine is a slightly bitter substance. The complex formed between caffeine and polyphenolic oxides such as theaflavins is the reason for the turbidity of tea soup after cooling. The complex of caffeine and theaflavins has a fresh and refreshing taste, which turns yellow and bright when cooled; Complexation with theaflavins, it appears dark yellow brown after cooling; Complex with thearubigins, it turns brownish red after cooling.
The sweet and mellow taste of black tea is mainly due to the presence of sugar substances in the leaves. The sugar substances in withered leaves, such as starch, produce more soluble sugars; During the high-temperature drying stage, the cracking of polysaccharides increases the amount of soluble monosaccharides. Therefore, the amount of soluble sugars increases during the production process of black tea, and the increase in soluble sugars has a positive impact on enhancing the sweet and mellow taste as well as the sweet aroma of the tea soup.
3. Changes in aromatic substances
The changes in aromatic substances during the production of black tea are quite complex, increasing from 50 in fresh leaves to nearly 300 in finished tea. There are so many types of aroma components, but the content of aroma is very small.
Part of the aroma compounds in black tea are inherent in fresh leaves, while the majority are transformed from other substances during the production process of black tea. During withering and fermentation, oxidation of certain alcohols, degradation of amino acids and carotenoids, esterification of organic acids and alcohols, oxidative degradation of linolenic acid, isomerization of hexenol, and thermal conversion of sugars all produce many new aroma substances. Therefore, during the withering and fermentation process, aromatic substances increase.
During the drying stage, due to high temperatures, many low boiling aromatic substances evaporate in large quantities, leaving behind some high boiling aromatic substances, mainly alcohols and carboxylic acids, followed by aldehydes, esters, etc. The composition and quantity of aromatic substances reach their peak during the fermentation stage. When a strong aroma is emitted, fermentation should be stopped in a timely manner to obtain high aroma tea. After baking, the content of aromatic substances decreases again, but the types of ingredients increase significantly.
