In the formation of Pu'er tea quality, besides heat-moisture reactions and oxidation reactions, the fermentation involving microorganisms is very important for quality formation. Among existing research, the main microorganisms discovered are as follows:

1. Aspergillus niger

Aspergillus niger is a lower eukaryote. As a globally recognized safe and edible microorganism, it holds an important position in industrial production and academic research. As a key strain involved in the formation of Pu'er tea quality, studying its life cycle and metabolic changes is of great significance.

During the large-scale production fermentation and pile-fermentation process of Pu'er tea, the number of Aspergillus niger is always in a dominant position. Aspergillus niger can produce both intracellular and extracellular enzymes, including about 20 types of hydrolases, such as glucoamylase, cellulase, and pectinase. These can decompose organic substances including polysaccharides, fats, proteins, natural fibers, pectin, and non-soluble compounds. The hydrolysis products are mostly monosaccharides, amino acids, hydrated pectin, and soluble carbohydrates, making it easy for the effective components in the tea leaves to leach out and diffuse. This lays a solid material foundation for enhancing the taste of the tea infusion and forming the smooth and mellow quality characteristics of Pu'er tea. Therefore, the organic acids and enzymes produced by the metabolism of Aspergillus niger during the fermentation of Pu'er tea play an important role in the formation of Pu'er tea quality. Moreover, during the pile-fermentation of Pu'er tea, Aspergillus niger always acts on Pu'er tea as a dominant microbial community.

2. Penicillium genus

During the pile-fermentation of Pu'er tea, Penicillium produces various enzymes and organic acids. At the same time, the penicillin produced by the metabolism of Penicillium chrysogenum may have a good inhibitory and eliminating effect on miscellaneous bacteria and spoilage bacteria. Therefore, we believe that Penicillium chrysogenum has an auxiliary role in the formation of the mellow quality of Pu'er tea.

3. Rhizopus

Rhizopus has high amylase activity, can produce organic acids, and also generates aromatic ester compounds. However, because of its strong pectinase secretion ability, the softening of tea leaves during Pu'er tea pile-fermentation is also related to the proliferation of this mold. In each stage of pile-fermentation, controlling appropriate temperature and humidity to increase the proportion of Rhizopus is beneficial for forming the sticky, smooth, and mellow quality of Pu'er tea.

4. Aspergillus glaucus

This strain can cause food decay and spoilage. Its proliferation should be avoided as much as possible in production. Experiments show that it appears more frequently in large-scale production, but rarely appears in simulated and sterilized pile-fermentation processed Pu'er tea, and disappears in the later stage. Therefore, controlling the pile temperature and improving the hygienic conditions of tea processing are conducive to forming the pure quality of Pu'er tea. Yeast genus and Pu'er tea yeast genus are important strains for the formation of Pu'er tea quality.

5. Yeast

During the pile-fermentation of Pu'er tea, the heat-moisture effect creates a favorable environment for the metabolic activity of yeast, enhances enzyme activity, and also provides a heat source for the chemical changes of tea components. In addition, molds can utilize various polysaccharides as carbon sources for sugar metabolism and produce a large amount of polysaccharides and monosaccharides, providing sufficient nutrition for yeast to proliferate rapidly. When creating an environment conducive to the proliferation of yeast, it multiplies quickly, and the quality of the processed tea leaves appears sweet, fragrant, mellow, and smooth. It can be seen that the formation of the sweet, mellow, and smooth quality characteristics of Pu'er tea is directly related to the growth and decline of yeast. That is to say, the quality characteristics of Pu'er tea, such as aged aroma, mellow, sweetness, and smoothness, are inseparable from the dominant strains during the fermentation process.

Yeast plays an important role in the formation of Pu'er tea quality. If the quantity is properly controlled during the pile-fermentation process of Pu'er tea, it can increase the effective nutrients and health-beneficial substances in Pu'er tea, endowing it with unique therapeutic quality characteristics that distinguish it from other types of tea. It is also beneficial for forming the sweet, mellow, and aromatic quality style of Pu'er tea. However, if improperly controlled, it can form undesirable substances such as spicy, irritating, tingling, numbing, hanging, locking, and sour flavors, affecting and reducing the quality of Pu'er tea. Therefore, the quality characteristics of good Pu'er tea, such as smoothness, mellow thickness, liveliness, smoothness, and aged aroma, are closely related to the role of yeast in Pu'er tea pile-fermentation.

6. Bacteria

During the pile-fermentation of Pu'er tea, the number of bacteria is extremely low, and no pathogenic bacteria have been found. This is the result of antagonistic effects among various microorganisms. For example, the extensive proliferation of yeast and molds can inhibit the growth of bacteria. At the same time, domestic and international studies have shown that tea polyphenols in tea leaves can also inhibit the growth and reproduction of bacteria that are pathogenic to humans or animals.

During the pile-fermentation process of Pu'er tea, in addition to the above-mentioned microorganisms, there are also a small number and a very small number of undetected microorganisms. Combining the research results on the growth and decline changes of main microorganisms during Pu'er tea pile-fermentation and their relationship with quality, it can be seen that the microbial strain changes during Pu'er tea processing are extremely complex. From the comparative analysis of different treatments, it is known that Aspergillus niger is always in a dominant position, the total number of yeast is second, the number of bacteria is extremely low, and no pathogenic bacteria have been found. During the pile-fermentation of Pu'er tea, these microorganisms all play a role in the formation of Pu'er tea quality.