Aging Pu-erh tea: wet storage vs. dry storage (Part I)

Posted by Boyka Mihaylova on

Pu-erh is among the most fascinating and controversial topics in the world of tea. Today, we will speak about a major aspect of the Pu-erh tea production cycle: aging or storage. There are two primary schools of thought: wet storage and dry storage. Let's explore their differences and the way they affect Pu-erh tea quality.


What is Pu-erh tea?

Pu-erh tea is a fermented tea common in China. According to the National standard, it has a Protected designation of origin (PDO). That means only tea grown and produced in Yunnan province can go by the name of Pu-erh. It has a history of more than 2000 years. Pu-erh tea, as we know it today, appeared during the Ming dynasty (1368 – 1644). However, people in Yunnan cultivated tea as early as the Eastern Han dynasty (202 BC – 220 AD). Later, during the Tang dynasty (618 – 907 AD), they started to trade with it along the borders of the empire, which led to the creation of the Ancient Horse and Tea Road.


What are the differences between Pu-erh tea variations?

Pu-erh tea exists in two variations. As with other major tea types, the main difference lies in the production process.

  • Raw Pu-erh (Sheng Pu-erh – 生普) is a variety made from the fresh leaves of the Big Leaf variety (Da Ye Zhong – 大叶种) of Camellia Sinensis. The traditional processing method includes several stages. First, farmers pick the leaves and leave them in the shade to wither. They then roast them over a high fire to halt the oxidation. After that, they roll the leaves to get rid of excessive moisture. Finally, they dry them in the sun. The result is a semi-processed loose tea, called maocha, which workers further steam and compress into Raw Pu-erh cakes.
  • In a nutshell, Ripe or cooked Pu-erh (Shu Pu-erh – 熟普) is Sheng Pu that undergoes microbial fermentation. It occurs during a processing stage called "wet piling", or Wo Dui (渥堆). That is done by piling a big amount of maocha and sprinkling it with water. Increasing the humidity and temperature gives birth to a unique microflora of molds and bacteria that start to ferment the leaves. After a certain period (usually 40 to 60 days), the workers unpile and ventilate the tea. They then press it into various forms, including cakes and bricks.


a kind of fermented tea common in China


What is aging, and how does it affect Pu-erh tea?

Aging is the last step in the Pu-erh production cycle. It is also a key component for the quality of the end product, along with the raw material and production process. We need to understand what happens with tea during the storage phase to understand its importance.


Post-fermentation explained

Pu-erh belongs to the category of post-fermenting teas. This process includes three factors:


  1. Internal oxidation (aka endo-oxidation): the transformation of the tea under the influence of enzymes inside the leaves. Although most enzymes have been deactivated during the Killing green stage, part of them remains alive. With time, they continue to transform the leaves from the inside. That is the slowest part of the process. 
  2. External oxidation (aka exo-oxidation): This describes the action of the oxygen coming into contact with the tea leaves. It's a quicker process than endo-oxidation. It's also one that needs to be monitored and controlled. Too much access to oxidation will deplete the leaves from aroma and taste, making the tea dull and bland.
  3. Fermentation: This is the effect that some bacteria and mold produce on the tea leaves. Their activity transforms the tea taste, aroma, and mouthfeel. The bacteria require a certain amount of water (humidity) to develop. If the moisture amount is too low, there will be no microbial development; if it's too high, it will lead to the growth of harmful and toxic microflora.


The storage and aging of Pu-erh tea is the combined effect of some, or all of the above processes on tea leaves over time.


With time, two main styles formed for storing and aging Pu-erh tea: wet storage (Shi Cang, 湿仓) and dry storage (Gan Cang, 干仓). Let's explore how both affect the Pu-erh tea quality.


What is wet storage, and how does it influence Pu-erh tea quality?

Wet storage refers to storing tea leaves in a humid environment, often with an elevated temperature. The high moisture causes an explosive growth of mold and bacteria. In turn, this shortens the storage time. Wet storage makes the tea age much faster. However, it also hides some hazards. 


• Aging Pu-erh tea: natural wet storage

It's worth noting that when we speak of wet storage, it might refer to natural climate conditions, as well as artificially controlled ones. Some wet storage representative areas include Hong Kong, Guangdong, and Taiwan. The average air humidity in all of these places exceeds 80% during most of the year. Storing the tea there lets it experience a naturally humid environment and its effects. We call this kind of storage natural wet storage.


• Aging Pu-erh tea: artificial wet storage

Wet storage can also refer to storing the tea in an environment with artificially elevated moisture. The high humidity forces the tea to quickly "ripen". That way, it becomes profitable and could be sold more rapidly than waiting for it to age normally.


Transformation is a major advantage of Pu-erh tea. It defines its market value and quality range. To achieve a good transformation, we need a combination of controlled oxidation and fermentation to occur in tea leaves. Both of these processes happen with wet and dry storage. However, the outcome is quite different.


• Wet storage advantages

Fermentation is part of the aging process. It is a result of the activity of microorganisms, which need water to develop and thrive. The elevated moisture in wet storage causes mold and bacteria surges, enhancing the tea leaves' fermentation. Some of the good effects of wet storage include:

  • Notable shortening of the time required for aging the tea
  • Sweet taste
  • Lubricated, "oily" mouthfeel of the tea soup
  • Development of a specific "wet" flavor, prized by some tea lovers & collectors 
  • Rich microflora

However, this is where it gets complicated. 


Yunnan tea


•Wet storage shortcomings

Too much of a good thing is not necessarily a good thing. An example of such practice is the Hong Kong tea market in the 90s. Back in time, there was a growing demand for tea with a more mellow taste and "aged" flavor. That applied both to the inland market, as well as Hong Kong, Taiwan, and some countries in South-Eastern Asia, like Malaysia. Hong Kong was a major tea hub, catering both inland and abroad. However, space in Hong Kong was (as it is today) notoriously scarce and therefore expensive. Lots of tea merchants couldn't afford to build or use professional warehouses. They then stacked their teas in port cabins, in damp and stuffed spaces (some people believe that's when the "fishy smell" notion appeared), or in low-rent underground warehouses. 

Increased moisture and lack of ventilation caused more harm than good in tea leaves. It took years to notice the adverse effects of the wet storage, some of which include:

  • Formation of peculiar smells (i.e., heave warehouse smell, fishy smell, musty smell, earthly smell, and so on)
  • Harmful bacteria outbreak
  • Formation of carcinogenic substances as byproducts of some microorganisms' activity
  • Tea molding, musting or rotting
  • Lower quality - heavy, unpleasant taste; loss of aroma; muddy, turbid tea soup


The game-changer in aging Pu-erh

Things with wet storage changed in the year 1989. That's when a tea collector, Mr. Chen Qiang, purchased a 30-tons batch of Menghai Tea Factory Pu-erh. Unlike the current practice, he didn't transport it to Hong Kong but stored it in Kunming instead. 5 years later, he sold it to the owner of TeaArt Paradise, Mr. Chen Guoyi. Mr. Qiang was unhappy, as this tea didn't sell well in Hong Kong – people found it too green and astringent. By then, Mr. Guoyi didn't know anything about pu-erh tea. He only sold green tea, oolong, and teaware. While tasting the sample that Mr. Qiang brought with him, he was shocked to discover a tea with a remarkably strong and sharp taste, yet quite fragrant and brew-resistant. Mr. Guoyi bought all the amount (about 350 cakes), naming the series "Ba Ba Qing Bing", or "88 Qing Bing" (八八青饼), and a collector's legend was born.


88 Qing Bing and the birth of dry storage

By the time Mr. Guoyi bought the cakes, their price was roughly ¥20/cake. Due to the lack of space in his small shop, he had to continue storing the tea in Kunming. He sold more of it each year, and the price grew exponentially. In 2020, two tubes of the BaBa Qing Bing auctioned at 1.725 million yuan! More than 30 years after the initial purchase, the tea remains moist and oily, sweet and long-lasting, according to tea lovers, lucky to taste it. That is arguably the most successful investment in the history of Pu'er tea. Since then, "88 Qing" gained the "founder of dry storage" reputation.


That's all for today! Next week, in the second part of this article, we will discuss the phase of transitioning from wet to dry storage. We will then explore their advantages and shortcomings, and give an answer on whether wet storage is good or bad after all. You will learn the two essential factors that guarantee effective storage for your tea cakes. You will also understand how the shape influences tea storage. Finally, you will get to know the best ways to storing and aging Pu-erh at home, depending on its shape and quantity. Stay tuned!