Speaking of tea, people often say full fermentation, semi-fermentation and light fermentation. Is this the same fermentation as our common fermented foods such as yogurt, wine and vinegar? What is the difference between them? Let's learn about the fermentation of tea together ~
How does tea fermentation affect human health?
Usually, fermentation refers to some kind of decomposition process of organic matter by organisms. Fermentation has long been recognized by people, but it is nearly 200 years to understand its essence. Fermentation strictly defined by microbial physiology: the process that organic matter is degraded into oxidation products by biological oxidation and releases energy is collectively called biological oxidation.
industrial fermentation
In industrial production, any industrial production realized by microbial life activities is generally called fermentation, such as beer brewing and monosodium glutamate production. Fermentation in food: Fermented food refers to a kind of food with unique flavor processed by beneficial microorganisms, such as yogurt, cheese, distiller's grains, kimchi, soy sauce, vinegar, lobster sauce, yellow wine, beer and wine.
Biological oxidation of tea
It is often said that China tea can be divided into six categories according to the degree of fermentation and comprehensive methods. But the word "fermentation" here, in the customary context of China tea, is completely different from the above microbial fermentation. In tea, the same green leaf is processed into green tea, black tea and oolong tea by controlling biological oxidation, which is also wrongly called fermentation. This process is more like a series of enzymatic reactions, perhaps it should be called biological oxidation. The biological oxidation of tea is a series of oxidation processes of catechins promoted by oxidase existing in the cell wall after the cell wall is damaged.
In the cells of tea, catechin exists in the cell sap, while oxidase mainly exists in the cell wall, not mainly in microorganisms, so it is necessary to break the cell wall. This naturally explains why fermented tea needs to be twisted. According to the different oxidation degree of polyphenols, full fermentation, semi-fermentation and light fermentation are also distinguished. In black tea, polyphenols are highly oxidized, which is called full fermentation; The oxidation degree 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 catechins contained in tea. The color of leaves changed from green to copper red, which formed the unique color of black tea. After the liquid cell membrane of tea leaves is destroyed, polyphenols, amino acids and other substances in vacuoles are gradually oxidized. At the same time, due to the oxidation of catechins, some substances in tea have chemical reactions, resulting in the unique color, flavor and quality of black tea.
The above is the basic meaning of China tea fermentation. However, because there are many kinds of tea in China, the processing techniques and methods are rich and colorful, and the definition of quality formation is different, in the process of making and quality formation of some tea, in addition to the fermentation in the sense of biological oxidation of the above-mentioned enzymatic reaction, some links will also involve microorganisms.
Tea "fermentation" is not an accurate term. Biological fermentation is to convert some ingredients in food into other ingredients through the growth of microorganisms, such as sauerkraut fermentation to convert carbohydrates into lactic acid and acetic acid, wine fermentation to convert carbohydrates into alcohol, and soy sauce fermentation to hydrolyze protein. In the process of tea processing, the characteristics of yellow tea, oolong tea, white tea and black tea do not need the participation of microorganisms. One of their reactions is the oxidation of tea polyphenols in different degrees (such as the so-called "semi-fermentation" of oolong tea and the "full fermentation" of black tea) and the reaction caused by enzymes of fresh tea leaves, such as the withering of white tea. Some teas will have the process of baking and aroma enhancement, and Maillard reaction and caramelization reaction will occur in the process, which has nothing to do with microorganisms.
In these processes, the products of reaction, enzymatic reaction and non-enzymatic reaction have not found any ingredients that "affect human health".
Only black tea, including Anhua black tea, Ya 'an Tibetan tea and Yunnan Pu 'er tea, really exists in the process of biological "fermentation". In the process of making these teas, there will be a natural fermentation step, that is, naturally occurring microorganisms will grow in them. After the black tea is soaked, it will retain a relatively high water content (generally, the water content is around 12%). At this water content, microorganisms can still have a certain growth ability. In other words, black tea will slowly ferment during storage.
The public's doubt about tea fermentation lies in whether toxins, especially aflatoxins, will be produced during fermentation. Based on people's research on Pu 'er tea fermentation, the raw materials and fermentation conditions of tea are not suitable for the growth and production of aflatoxin. According to the reported research and test results of Pu 'er tea fermentation, it can be considered that the standardized fermented Pu 'er tea will not produce harmful substances such as Aspergillus flavus, but during the storage process, some Pu 'er tea is stored in a poor environment (such as "wet stored Pu 'er tea" deliberately selected in a humid environment), which may be contaminated by mold or mycotoxin in the environment. The latter is actually a possible phenomenon in all kinds of food storage, which has nothing to do with the fermentation of tea.
At the other extreme of tea fermentation, it is believed that fermentation produces many "nutrients" or "bioactive substances", so it produces various effects. Fermentation can indeed produce some substances that are not available in industry, but whether it is valuable to human health needs to be verified by clinical trials, and it cannot be "deduced" only by theoretical "speculation" or cell experiments and animal experiments. At present, we can see many research papers about the "XX efficacy" of various specific teas and report many "efficacy experiments". But these papers can basically only be used for marketing copy, and if they are analyzed as scientific evidence, they are far from enough to prove the "conclusion".
In a word, tea is a very healthy drink. Different techniques and different tea varieties mainly affect the flavor and taste of tea. That's all for now ~