The main causes of sour Pu 'er tea are:
1 is caused by sour substances contained in tea itself.
2. There are too many tides (backwater and water supplement) during heap fermentation, and the fermentation time is short because of quick success and instant benefit.
Sour substances in tea are the general name of substances with acidic taste. Mainly various organic acid compounds, such as citric acid, malic acid, succinic acid, ascorbic acid, gallic acid, free acidic amino acids, weakly acidic tea polyphenols and so on. Acetic acid (acetic acid) contained in "sour" Pu 'er tea is metabolized by lactic acid bacteria in "heap fermentation"; Propionic acid will also be produced in large quantities under the action of lactic acid bacteria; Pentanoic acid is the main component of sour Pu 'er tea, which is produced by microbial fermentation. The forms of decanoic acid and nonanoic acid are closely related to microbial action. In the process of "heap fermentation", if the process is not handled properly, a large number of the above sour substances will be formed, resulting in "sour" Pu 'er tea.
In addition, oxygen is an essential element in Pu 'er tea fermentation. Free oxygen in the air is not very reactive, and once it is combined with other substances, oxygen can act. The oxidative decomposition of polyphenols, aldehydes, ketones, lipids, vitamin C and other substances in tea, whether enzymatic oxidation or enzymatic oxidation, aerobic oxidation or dehydroxylation oxidation, can be completed and thoroughly with the participation of oxygen. The pile of Pu 'er tea has too much water content, poor air permeability and lack of oxygen, which makes the above oxidation difficult to complete, and even produces anaerobic respiration, producing a large number of anaerobic bacteria and spoilage bacteria, which directly leads to a large number of alcohol substances, making tea sour, soft and sticky at the bottom of leaves.
The sour taste of piled tea is a common phenomenon in Pu 'er tea fermentation, which can usually be obviously detected 4 ~ 5 days after the start of fermentation, indicating that a violent chemical reaction has taken place in piled tea, which is a staged feature of Pu 'er tea fermentation. With the extension of time and the deepening of fermentation, many low-boiling aroma substances with pungent smell decompose and disappear in large quantities, and the "acid" gas substances also degrade and disappear gradually. In this process, if the soup is hastily piled up only by the change of soup color, the "sour" gas will not be completely lost, and the finished product will inevitably have sour taste. Therefore, the fermentation time is short and the degree is partial, which is also the reason why Pu 'er tea is "sour".