How to Store and Age Pu-erh Tea

In 2019, 2.2 kilograms of raw pu-erh tea made in the 1920s sold at a record breaking auction in Hong Kong for US$3,362,774 — approximately US$4,132,488.14 in today’s dollars.

How did a nearly 100 year old tea fetch such a high price? Thanks to proper storage.

One of the fundamental drivers of interest and investment in pu-erh tea is the idea that you can deliberately refine the tea’s aroma, flavour, and other characteristics through careful longterm ageing. 

In this article, we explore what pu-erh storage accomplishes, why it matters, and how to do it at home. 

An Introduction to Pu-erh

At first glance, fresh raw pu-erh tea looks a lot like green tea — this is somewhat unsurprising given that both types of tea go through almost identical steps of processing.

When brewed, both young raw pu-erh and green tea typically taste grassy and 'fresh', with plenty of astringency, some bitterness, and a sweet aftertaste. However, as anyone who has bought green tea knows, there’s an expiry date on some of the more fleeting characteristics. In time, green tea’s fresh aroma and vibrant flavours will fade, and eventually become dull and flat or stale. In short, there's not millions of dollars being splashed around for old green teas.

So, given the similarities between pu-erh and green tea… why would anyone pay exorbitant prices for an old raw pu-erh cake? 

The key to answering this is twofold.

The first part involves unpacking the critical differences between how pu-erh teas and green teas are made. We explore the topic of pu-erh tea production in our earlier articles — How Pu-erh Tea is Made Part 1 and Part 2.

The second part lies in understanding pu-erh storage: what its purpose is, what’s involved in effective storage, and how to do it yourself. 

The Purpose of Storing Pu-erh Tea

If you read our earlier articles, 'How Pu-erh Tea is Made' Part 1 and Part 2, you might recall how pu-erh tea processing ensures the survival of some enzymes.

Unlike green tea, the 'fixing' or 'kill-green' step where the fresh tea leaves are fired in a wok is done at a lower temperature for raw pu-erh tea, and less thoroughly. The less-than-100% denaturing of the enzymes in the leaves, as well as drying the tea leaves in the sun, preserves the microbes on the leaves, allowing them to age.

The purpose of storage then, is to take advantage of these surviving compounds in order to mature and further enrich the fragrance, flavour, and overall effect of pu-erh tea. 

When raw pu-erh tea is stored in a suitable environment (more on this in a second), its leaves undergo a series of complex microbial changes that transform the tea’s overall profile. If you appropriately store a recently made raw pu-erh for a many years, you can expect the tea to transform from green-hued, fresh and harsh, to red or brown hued, aged and smooth. A rough analogy for the transformation is the maturing of clear spirits in a cask to create whisky. 

Given enough time, all storage will accomplish some kind of transformation in pu-erh tea.

On one end of the spectrum, raw pu-erh tea that is stored in an extremely hot and humid environment will change very rapidly. After an only a few years, what was once fresh raw pu-erh will look and taste more like ripe pu-erh — smooth, fermented, and very dark. If the storage is particularly humid, the resulting tea might have an indolent (or ‘wet’ and ‘dank’) tinge to its aroma and flavour which some people find off-putting, whilst others consider desirable. This type of wet storage is sometimes called 'traditional storage', referring to historical practices in the 20th century particularly in places such as Guangdong, Taiwan, Hong Kong, and Malaysia. Tea would be stored in warehouses close to the sea ports, or in basements, and transform dramatically in a short time.



On the other end of the spectrum, a raw pu-erh tea that is stored in temperate or cool environments might look and taste remarkably similar to when it was first made, even after a decade or more years or storage. Some people may have a preference for this more conservative approach to storing and ageing their pu-erh tea, arguing that it preserves more of the original character of the tea.
 

In our experience, the most sought after aged pu-erh teas are ones that have undergone a storage approach that sits somewhere in-between these two extremes. This means the tea has been stored warm and wet enough, and for long enough that there are noticeable changes in its colour, flavour, and fragrance. The purpose of this kind of storage is to preserve and enhance some of the tea’s initial characteristics but without any detectable elements from the storage itself (i.e no ‘wetness’ or ‘dankness’). 

During the 1980's and 1990's, it was re-discovered that teas stored in less humid environments (such as warehouses higher up the hills in Hong Kong, or on higher floors of buildings) aged more slowly, but retained more fragrance, complexity, and mouthfeel compared to teas that fermented in only a few years. This has come to be called 'dry storage', though it should be noted that in this case, 'dry' is still quite humid (60-70%), just not extremely damp (80-100%). Increasing interest in pu-erh tea's ability to age in this manner contributed to its rising fame over the turn of the century, and the idea of pu-erh tea becoming an investment.  

It's important to note here that while storage can transform and enrich a tea's initial profile, there's a limit to what can change, and by how much. A moderate approach to storage is favourable in most instances, because it straddles the fine line between altering a tea beyond all recognition, and preserving a tea's original character with some (hopefully pleasant) additional complexity.

Regardless of your preferred storage approach, it's always best to start with a high-quality tea that already has desirable and appealing characteristics to you. If you store a low quality tea with unappealing characteristics (i.e. harsh on the throat, astringent to the point of sourness, lacking body or sweetness, etc) with the aim of improving its character through ageing, you may be disappointed with the outcome. 

To sum it all up, there’s a method to the madness of pu-erh storage. The more balanced the method (and the better the tea!), the more effective the proverbial madness.

Defining Effective Storage of Pu-erh Tea

Depending on your desired outcome, effective storage of pu-erh tea can involve many different approaches. In our eyes, effective storage meets the following criteria:

1. Encouraging sufficient microbial activity
2. Avoiding mould or other damage to the tea
   
3. Cost-effective and convenient to maintain
   

The role of microbial ripening


Ageing pu-erh tea is a process of microbial ripening.

Microbial ripening is a multilayered process in which bacteria, fungus, and yeasts — from both the environment and already on and in the tea itself — slowly transform the tea. Over the course of decades, the diversity and populations of these microbes fluctuate as their food sources change. One bacteria eats something and produces something else, which is perfect food for a certain type of fungus, and so on and on the chain of events goes.

These microbes have something in common — heat makes them work faster. Some of the major centres for pu-erh tea storage in the last half a century have been Guangzhou, Hong Kong, and Taiwan; all places with consistently hot and humid climates. Interestingly, Kunming, in northern Yunnan, is also a city where vast amounts of pu-erh tea are stored, although it has much cooler climate.

At the most basic level, tea that is stored in hot conditions ages more quickly than teas stored in cool ones. The storage environment's humidity plays a role too, but it is important to understand that humidity is fundamentally interlinked to temperature.

Relative humidity (RH) is expressed as a percentage of the air the is saturated with water, i.e how much water vapour is in the air compared to how much it can hold, at that specific temperature. As air temperature increases, for example by running a heater in a room, the relative humidity will go down if no extra water is added to the air.

While microbes depend on moisture to survive and reproduce, environmental (i.e. ambient) humidity is only part of the picture. The most important factor determining microbial survival is the moisture content of the tea leaves themselves — and what determines stable moisture content in the leaves? Well, as we just discussed, the temperature of the surrounding environment.


Let’s break it down a bit. 

Key factors behind microbial ripening

Tea is very hygroscopic; it absorbs and loses water from the air very easily and very quickly. For example, dried tea leaves can range from approximately 3-18% moisture by weight, depending on the type of tea and processing.

Think of a tea cake like a sponge; if the air is humid enough (meaning around 60-70% RH or above, depending on the temperature) it will continue to absorb water until it's fully saturated and can’t hold any more. When this happens, the risk of mould developing on the leaves rises dramatically. 

Similarly, if the air is dry enough (meaning at and below 45-50% humidity) the tea will leech water into the air until either the ambient humidity stabilises and reaches equilibrium, or the tea leaves have no more water to lose. In total, it’s possible for a pu-erh tea cake to lose about 97% of its overall moisture content in extremely dry conditions. The remaining 3% is water that’s locked inside of cells within the leaves; to dry this out too, you’d need to heat the leaves to approximately 100C (or 212F). 


When a tea dries out completely, it can lose its flavour and fragrance through volatilisation of the essential oils and other compounds. Once these compounds are no longer bound strongly enough by water, they essentially evaporate into the air.

To continue the sponge analogy, picture a huge warehouse room with nothing in it but a single tea cake. A tropical storm rolls in and the humidity in the room starts to climb to nearly 100% — meaning the air is totally saturated. That poor little tea cake absorbs as much humidity as it can but there’s only so much it can hold before it too is fully saturated, at which point it goes mouldy.

Now picture the same warehouse room, but filled floor to ceiling with hundreds of boxes of tea. The capacity of the sponge is much larger, and even a few days of elevated humidity is easily absorbed into the mass of tea. Once the storm has passed and the humidity begins to drop again, the tea will leach out some of the extra water it had absorbed, no problem, until a new equilibrium is reached. 

This is the mechanism at play in warnings we’ve heard from people in places like Guangzhou, telling us that tea in the warehouse storage will be just fine — but grab a single tea cake to drink at home, leave it on your kitchen counter, and it'll go mouldy.

By understanding the basic principles of humidity, temperature, and equilibrium with the environment, we can approach storing tea at a smaller scale (such as at home) with a few good principles to take the pedantic guesswork out of it.

 A good problem to have: opened and unopened tongs in storage. The challenge is to not drink through everything, but it's easier said than done.

How to Store Pu-erh Tea at Home

Now that we’ve unpacked the basic principles behind effective storage, we can move on to sharing our tips for storing pu-erh tea at home.

A good storage has the following characteristics:

1. It’s free from pests, sunlight, and strong smells.

Because it’s highly hygroscopic, tea is incredible at absorbing fragrance from an environment. For this reason you want to keep the tea in some kind of resealable food-grade (unscented) bag or container, and away from any strong scents including household cleaning chemicals, incense/scent sticks/oil burners, herbs and spices, cigarette and vape smoke, perfumes and fragranced cosmetics, mothballs, and so on.



2. It has stable climatic conditions. 


This means avoiding an environment that undergoes any extreme swings in temperature or humidity.


To put things in even more basic terms, don’t set up your storage near a heater or air conditioner, near any sources of open flames (i.e. 9 times out of 10, the kitchen is no-go), close to a window, or in an excessively humid room (i.e. not the bathroom, laundry room, kitchen, near a leaky roof/wall/pipe, or garden shed, etc). 



Common sense goes a long way, but if you’re hardcore stickler for details, a control freak, or on the road for large portions of the year (like us), we recommend investing in a basic temperature and humidity monitor (AKA a thermometer and hygrometer) for peace of mind and peace in your heart. This way you can get advance notice on any conditions approaching mould risk territory.

3. It is easy to access and monitor, and serves your end goals.

Somewhat self explanatory, but ideally you want to strike a balance between longterm entombment and moderately-easy access to the stored tea.

While you might not plan on drinking it any time soon, easy access to the tea means it’s easier to catch and correct any issues before they spiral out of control. 

This might seem pedantic, but trust us; some rooms seem stable until the dead of winter/peak of summer. It’s always preferable to catch problematic factors early on in the storage journey, than to find the tea in a bad or undrinkable condition due to years and years of unmitigated exposure to undesirable elements within its storage environment. 

Conclusion

And that concludes our tips on how to age pu-erh tea at home through effective and intentional storage. This isn’t the only way to store pu-erh tea, but it’s how we like to do it.

If you have any further questions on the topic or interesting experiments to share with us, we’re all ears - send us a message on Instagram @kuuracorp or fill out our Contact Form.