Stored Tea

The storage time and conditions are crucial for the quality of tea, affecting its chemical components as well as its aroma, taste, and biological activity.

Therefore, investigating the changes in chemical components during tea storage is of great significance to maintaining or improving tea quality and enhancing its economic benefits.

One, Polyphenols

Polyphenols are important bioactive substances separated and purified from tea leaves, accounting for 18% to 36% of the dry weight of tea.

The changes and levels of polyphenols in Pu'er tea have a significant impact on its quality.

Generally, polyphenols in Pu'er tea tend to decrease to varying degrees during natural storage.

Feng Chaohao et al. found that the content of polyphenols in Pu'er tea decreases with extended storage time and higher temperatures, and the decline is more pronounced in teas with higher moisture content.

Luo Longxin et al. discovered that the total polyphenol content tends to increase initially and then decrease later.

Wang Yang's study showed that catechin content generally decreases, with raw cakes showing a larger and more noticeable change, while ripe cakes and loose tea show a relatively mild and less obvious change.

Two, Amino Acids

The content and composition of amino acids in tea, as well as their degradation and transformation products, all affect the quality of tea.

Amino acids in Pu'er tea are not only important substances for the freshness and aroma of the tea soup but also have a significant impact on the color of the tea soup.

Wang Ruyun et al. and Lin Changxin's studies both indicated that the amino acid content in Pu'er tea decreases over the storage period.

Gong Jiashun's experimental results showed that the content of amino acids in Pu'er tea shows fluctuating changes during storage, with the total amino acid content generally decreasing after storage. The composition and proportion will also undergo noticeable changes.

Pu'er tea stored for more than three years will have a significantly low amino acid content.

Short-term storage experiments have shown that, whether it is raw or ripe Pu'er tea, the content of soluble proteins will increase with extended storage time; for example, in the first four months of storage, the content of raw Pu'er tea increased from 2.93% before storage to above 3.7%.

Feng Chaohao et al. and Zhang Xia et al. found that the content of amino acids decreases while the content of soluble sugars increases with extended storage time.

However, Gong Shuying et al. demonstrated that the content of soluble sugars decreases with extended storage time and higher temperatures.

Three, Alkaloids

Alkaloids mainly include Caffeine, theobromine, theophylline, adenosine, etc.

Caffeine, theobromine, and theophylline are bitterness-contributing substances in tea, while adenosine enhances the freshness.

With prolonged storage, the caffeine content in raw Pu'er tea shows a decreasing trend, with a reduction of up to 25%, while the caffeine content in ripe Pu'er tea shows an increasing trend.

Liang Mingzhi's research indicates that if ripe Pu'er tea is stored in a dry-wet warehouse, its caffeine content will show fluctuating increases; the caffeine content in raw Pu'er tea is related to the storage environment, showing fluctuating decreases in dry warehouses and increases in wet warehouses.

In addition, due to the stable physical properties of caffeine itself, its changes are relatively small compared to other biochemical components.

Four, Water-Soluble

Components

Water-soluble substances and total soluble sugars have a very important impact on the quality of Pu'er tea. They are the main substances that form the sweet and mellow taste of tea and indirectly affect the aroma of the tea.

Related studies have shown that in the process of storing Pu'er tea, the water-soluble content in raw cakes generally decreases with storage time, while ripe cakes and loose tea show an increase.

Under normal temperature conditions, with extended storage time, the content of water-soluble substances will first increase and then show a slow downward trend after 25 days.

Total Soluble Sugars in Pu'er Tea

Studies have shown that with extended storage time, the total Sugar content in both raw and ripe Pu'er tea at different storage stages shows an upward trend, with an increase in the content of total soluble sugars in the tea soup.

Four, Aroma Components

Commonly recognized major aroma components include terpenoid compounds, glycoside degradation products, Maillard reaction, and lipid oxidation degradation products.

The unique aged aroma of Pu'er tea is closely related to the raw materials, the participation of microorganisms during fermentation, and subsequent storage.

The aroma components of Pu'er tea undergo significant changes during storage, with a decrease in the total content of volatile aromas, but an increase in the number of aroma components.

The proportions of low-boiling point and high-boiling point components relatively decrease, while the proportion of medium-boiling point aroma components increases.

The increase in components such as dihydroneryl alcohol, heptadienal, and pentenol is the reason for the unique aged aroma.

Some text and images are from the June 2025 issue (Volume 46, Issue 2) of the Tea Communications, titled “Research Progress on Factors Affecting Pu'er Tea Storage and Quality Changes.”