All kinds of tea fermentations

Some friends who have experience in tea drinking know that there are seven major types of tea in China: green tea, black tea, white tea, yellow tea, green tea (oolong), dark tea, and Puerh tea (whether Puerh is classified as dark tea or not). The division of different teas is not just the "color" we see, but is related to a professional term "fermentation degree".
Judging from the degree of fermentation, there are unfermented tea, lightly fermented tea, fully fermented tea, post-fermented tea, etc. So what changes have been made to the tea by fermentation, and what benefit will it have on the tea?

　　What is tea fermentation?

　　Fermentation of tea, that is, a series of reactions such as oxidation and hydrolysis that occur inside the tea in a special environment (including enzymes, hot and humid environment, etc.). Its essence is that the oxidation produced by polyphenol oxidase and peroxidase promotes the change of tea polyphenols.

Tea leaves are twisted to break the cell wall, which is more conducive to late fermentation.

　　The benefit of fermentation on tea:

　　 During the fermentation of tea, the oxidation of tea polyphenols is the main change. It will hydrolyze proteins, polysaccharides and other substances, and form some aroma components, which play an important role in the formation of tea flavor quality. Therefore, the degree of fermentation of tea is mainly reflected in the color, aroma and taste.

Comparison of various teas:

　　 Color change: light yellow-green-dark brown red.

　　 During the tea fermentation process, colorless tea polyphenols are oxidized into red substances under the action of oxidase and oxygen and in a certain temperature and humidity environment. These red substances are collectively called tea pigments. Unfermented tea leaves are green. After fermentation, the tea leaves and soup color will appear red, and the higher the degree of fermentation, the more red the color. So by looking at the green or red color of dry tea, tea soup and leaf bottom, you can roughly understand the degree of fermentation of the tea.

The change of aroma: slight aroma into aged fragrance.

Unfermented tea presents a green fragrance type; after mild fermentation (about 20%-30%), it will show a floral and fruity fragrance; when the fermentation degree reaches about 60%, it will show a mature fruity type; if it is made by full fermentation Caramel flavor is presented; after fermentation tea reaches a certain degree of fermentation, it will present a medicinal aroma and an old aroma.

Change in taste: reduced bitterness, increased moisture and sweetness.

The lower the degree of fermentation of tea, the closer to the flavor of natural plants; increasing the degree of fermentation of tea will make the tea lose more of the original taste of natural plants, but the bitterness of tea polyphenols after oxidation is reduced, and the tea soup will become more mellow. The irritation will also be reduced, and the hydrolysis of polysaccharides and proteins will increase the content of small molecule sweet sugars and amino acids, increasing the sweetness of the tea soup.
　How to make tea ferment?

　　 There are two methods. One is the oxidation of tea polyphenols under the action of the tea's own oxidase, that is, the tea leaves that have not been greened, rely on the activity of their own oxidase to oxidize the tea polyphenols in the case of cell disruption, such as black tea and Oolong tea fermentation.


　　Another kind is the oxidation of tea polyphenols under the action of foreign enzymes. Fermentation under the action of foreign enzymes is also commonly referred to as post-fermentation. This requires the tea to be green, to allow the fermentation to be fixed to a certain extent, and then to allow the tea polyphenols to continue the oxidation process under the action of microorganisms and oxygen, such as Puerh tea .

　　Simply put, it is the oxidation process of active enzyme under certain temperature and humidity.
Degree of fermentation of various teas:

The classification of the seven major teas is based on the degree of fermentation: green tea is non-fermented tea, white tea and yellow tea are lightly fermented tea, green tea (oolong tea) is semi-fermented tea, black tea and Puerh tea are post-fermented tea, and black tea is full Fermented tea. Among them, Puerh fresh tea has a low fermentation degree and a high freshness, while the fermentation degree of freshly cooked tea and sun-dried black tea is generally 60 to 70%. After it is made, after fermentation, the post-fermentation continues. Therefore, cooked tea, sun-red tea and other tea products use a slightly lower degree of fermentation, the tea product has a stronger plasticity, and the later conversion potential is greater.

It can be said that the degree of fermentation leads the tea to different classifications, resulting in a variety of styles that show the different charm of tea. Whether it is the traditional original flavor or the popularized fermented tea, every friend can choose the one that suits you best.

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What happens during tea fermentation?

Speaking of tea, people often say full fermentation, semi-fermentation, light fermentation. Is this the same fermentation as our common fermented foods such as yogurt, wine, and vinegar? What are the differences between them? Let’s take a look at the fermentation of tea.
What is fermentation?

　　 Commonly referred to as fermentation, it refers to a certain decomposition process of organisms for organic matter. The phenomenon of fermentation has long been recognized by people, but it has been almost 200 years to understand its essence. Strictly defined fermentation of microbial physiology: The process of organic matter being oxidatively degraded by organisms into oxidation products and releasing energy is collectively called biological oxidation.

　　 Fermentation defined in industrial production, industrial fermentation.

　　Industrial production generally refers to all industrial production that depends on the life activities of microorganisms as fermentation, such as beer brewing and monosodium glutamate production. Fermentation in food: Fermented food refers to a type of food manufactured by people using beneficial microorganisms, with unique flavors, such as yogurt, cheese, wine brew, kimchi, soy sauce, vinegar, tempeh, rice wine, beer, wine, etc.

　　Tea fermentation, biological oxidation.

It is often said that Chinese tea is divided into six major types of tea according to the degree of fermentation and the comprehensive manufacturing method. However, the term fermentation here is completely different from the above-mentioned microorganism fermentation in the traditional context of Chinese tea.

　　In tea leaves, the same green leaf is processed into green tea, black tea, oolong tea, etc. by controlling biological oxidation. This process is also mistakenly called fermentation.

　　 This process is more like a series of enzymatic reactions, perhaps it should be called biooxidation. The biological oxidation of tea leaves is a series of oxidative processes that promote the formation of catechins after the cell wall is damaged.

　　In the cells of tea, catechins are present in the cytosol, and oxidases are mainly present in the cell wall, rather than mainly in microorganisms, so the cell wall needs to be damaged. This naturally explains the reason why fermented tea needs to be twisted. According to the different oxidation degree of polyphenols, it can be distinguished from full fermentation, semi-fermentation and light fermentation.

In black tea, the degree of oxidation of polyphenols is very high, which is called full fermentation; the degree of oxidation of polyphenols in oolong tea is about half, which is called semi-fermentation.

　　For example, in the processing of black tea, the purpose of fermentation is to oxidize the catechins contained in the leaves. The color of the leaves changes from green to copper red, resulting in the unique color of black tea. After the tea cell membrane is damaged, the polyphenols, amino acids and other substances in the vacuole are gradually oxidized. At the same time, due to the oxidation of catechins, some substances in the leaves are chemically reacted to produce the unique color and fragrance quality of black tea.

　　The above is the basic meaning of fermentation commonly used in Chinese tea.
Due to the wide variety of Chinese teas, the colorful processing techniques and manufacturing methods, and the different definitions of quality formation, in the production and quality formation of some teas, in addition to the above fermentation in the sense of biological oxidation in addition to their own enzymatic reactions, There will also be microorganisms involved in some links.

　　For example, in addition to enzymatic action, the fermentation process of Puerh tea cooked tea also involves microorganisms.

　　 After separation research, the main microorganisms are Aspergillus niger, Aspergillus oryzae, Aspergillus kawachii, Aspergillus griseus, Rhizopus, lactic acid bacteria and yeast. Nonetheless, it is necessary to distinguish clearly between fermentation involving microorganisms and fermentation in the sense of biological oxidation. Otherwise, the conceptual ambiguity may easily lead to misunderstanding of the formation mechanism of tea quality.

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