Thursday, June 25, 2020

What is 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, vinegar, etc.? What is the difference between them? Let’s take a look at the fermentation of tea .

What is fermentation

Generally speaking, fermentation 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, the same green leaf is processed into green tea, black tea, oolong tea, etc. by controlling biological oxidation. This process is also incorrectly called fermentation. This process is more like a series of enzymatic reactions, maybe it should be called biooxidation. The biological oxidation of tea 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, while oxidase is 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 divided into 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 color and fragrance quality unique to black tea.

The above is the basic meaning of fermentation that Chinese tea often says. However, due to the wide variety of Chinese teas, rich processing techniques and manufacturing methods, and 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 the enzymatic reaction In addition, there will be microorganisms in some links. For example, in addition to the enzymatic action, the fermentation process of Pu'er tea cooked tea also involves microorganisms. After separation and research, the main microorganisms are Aspergillus niger, Aspergillus oryzae, Aspergillus kawachii, Aspergillus griseus, Rhizopus, lactic acid bacteria and yeast. Nevertheless, it is necessary for us 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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