Why does Pu'er Tea need “aging”?

The term “aging” is a popular phrase used in the community, referring to the aging process of Pu'er tea, which we often refer to as post-fermentation. Strictly speaking, the term “aging” is not accurate. It is quite different from the post-fermentation of Pu'er tea because post-fermentation is not simply a matter of storage. It is not a simple warehousing concept but rather a special process similar to the wine cellar that can meet the conditions for aging. This special process is actually aging, known professionally in food chemistry as “after-ripening.”

“After-ripening” falls within the realm of tea storage chemistry in tea chemistry. For a long time, tea experts believed that only Pu'er tea needed aging and “after-ripening.” Later, they discovered that other types of tea also undergo “after-ripening.” “After-ripening” refers to the quality changes that occur when tea transforms from slightly raw to good during this process. Taking West Lake Longjing as an example, it has a noticeable “raw green aroma” when first produced, which disappears after one to two months of storage in a lime jar, revealing a high and fragrant aroma. Of course, different types of tea use different methods for aging, resulting in different “after-ripening” effects. Besides Pu'er tea, Hunan dark tea, and Guangxi Liubao tea, other types of tea have shorter aging periods, mainly aimed at eliminating the “raw green aroma” through a brief “after-ripening” period, revealing normal tea fragrance, becoming mellow, increasing the concentration of the tea liquor, and brightening the infused leaves.

There is a phenomenon worth noting: the emergence of “aged green tea,” “aged Oolong,” and “aged black tea” in the tea world, which represents another misunderstanding about tea aging. Because the aging of green tea, Oolong Tea, black tea, and yellow tea is a “non-enzymatic oxidation” process, requiring a short aging time. Otherwise, it leads to automatic oxidation of the tea polyphenols and catechins. Catechins dehydrogenate into quinones, which then polymerize into brown substances. The further oxidation intermediates combine with amino acids, proteins, etc., forming dark-colored high polymers. This causes the tea flavor to become weak, lacking astringency and freshness, thereby reducing the quality of the tea and turning it into aged tea. Since these teas undergo a high-temperature step in their initial processing, their chemical components are fixed. Further oxidation remains a “non-enzymatic oxidation” process, ultimately leading to “moldy change,” which is not a safe or healthy beverage.

However, Pu'er tea is different. Its aging is not “non-enzymatic oxidation” but “enzymatic fermentation.” “Enzymatic fermentation” uses endogenous enzymes and exogenous enzymes (provided by a specific environment) to intentionally degrade and condense the polyphenols in the tea, producing new compounds, including primary metabolites, followed by secondary metabolites, until the final product appears. Therefore, its aging process has relatively higher technical and environmental requirements and requires a longer aging time—twenty, thirty, or even fifty years. Perhaps because of the long time involved, we prefix “old” before Pu'er tea and habitually refer to it as “old tea.”

However, “old tea” does not equate to Pu'er tea stored for decades. In recent years, many people have misunderstood “old tea,” believing that any Pu'er tea stored for decades can be considered “old tea.” However, this is not the case. Some Pu'er teas over twenty or thirty years old cannot be called “old tea.” This situation usually arises from two reasons:

One is the “green tea mindset” during initial processing, introducing green Tea processing techniques from selection to production, giving Pu'er tea the “appearance” but not the “essence.” Changes such as converting “sun-drying” to “firing” will not transform the tea into “old tea” no matter how long it is stored. We typically view this phenomenon as a “genetic defect” and classify it as aged tea;

The second is oversimplifying the aging process of Pu'er tea, lacking professional aging conditions, or improper storage, leading to unsatisfactory transformation results and failing to meet the quality standards of “old tea.” It can only represent age but lacks the quality of “old tea.” It also falls under the concept of aged tea.

“Old tea” not only represents age but also symbolizes quality and a level of excellence. High quality is paramount.

Let us return to the original topic—”after-ripening.” It is actually composed of two main models: non-enzymatic oxidation and enzymatic fermentation.

Pu'er tea belongs to “enzymatic fermentation,” more accurately, “multi-enzyme system enzymatic fermentation.”

We might ask: What does “enzymatic fermentation” bring to Pu'er tea? Actually, answering this question also resolves another doubt: Why do we age tea?

The answer is straightforward—it is due to the principle of “the older, the more fragrant” in Pu'er tea, which is also its “after-ripening.”

What is “the older, the more fragrant”?

“The older, the more fragrant” is an illustrative description of the aging process of Pu'er tea. “The older” is a time concept, while “the more fragrant” is a quality concept. The aging process of Pu'er tea is the final processing step, critical for improving or recreating its quality.

Many people question the phrase “the older, the more fragrant.” They believe that there is no such thing as “the older, the more fragrant” for any tea. After a long storage period, tea loses its taste. Can it still be considered tea? Saying that Pu'er tea can be stored for a long time and improves in quality is deceptive, intended to encourage consumers to store large quantities of tea. This statement essentially turns consumers into seeing Pu'er tea as an investment tool, altering the inherent value of tea.

The denial of “the older, the more fragrant” by skeptics mainly stems from a literal misunderstanding of the phrase. They believe that since it is “the older, the more fragrant,” its aroma should be comparable to green tea or oolong tea. According to this understanding, Pu'er tea lacks the “fresh aroma” of green tea and the “unique aroma” of oolong tea. Moreover, regarding aromatic compounds, Pu'er tea is not “the older, the more fragrant” but rather “the older, the weaker.” Many “old Pu'er teas” have very weak aromas. This is sufficient proof that “the older, the more fragrant” in Pu'er tea is baseless.

However, in the Pu'er tea community, “the older, the more fragrant” should not be taken literally. It actually includes two meanings: First, after aging, Pu'er tea indeed contains aromatic compounds like camphor aroma, Orchid aroma, jujube aroma, etc., unique to Pu'er tea and significantly different from the aroma of green tea and oolong tea. The standards for tasting green tea and oolong tea should not be simply applied. Second, “the more fragrant” in “the older, the more fragrant” is not solely about aroma but rather a general concept of quality.

Which viewpoint is more persuasive?

In tasting green tea, we often use the “sensory evaluation” method to distinguish between qualities, such as the shape of dry tea, the color of the tea liquor after brewing, the appearance of the infused leaves, and the taste and aroma of the tea liquor. This evaluation primarily relies on visual observation, tasting, and experience, a historical method passed down and the oldest and most primitive way to assess tea. However, human eyes, mouths, and noses are not chemical analytical instruments and are unable to detect and differentiate the hundreds of internal components in tea and their respective concentrations, inevitably leading to errors in the assessment process, sometimes significant ones.