Outdoor & Indoor Pu’erh Storage in the West. Why Climate Data Only Tells a Partial Picture for Home Storage.

A while back I crunched the numbers for climates in some eastern and western cities and compared them to Kunming. One of the takeaways from that article is that despite its reputation, Kunming’s humidity is not that much lower than places with a more humid reputation, i.e. Hong Kong or Taipei. The more significant difference is in the temperature. On a similar note, Seattle (my hometown) is similar in relative humidity but is even colder than Kunming. Hotter air holds more water content and in that article I noted the sometimes under-emphasized importance of temperature. I stand by this, but I now read the climate data a little differently, especially when it comes to the implications of home storage in the west.
Quarterly Humidity/Temperature Information

Avg. Temp 1Q Avg. RH 1Q Avg. Temp 2Q Avg. RH 2Q Avg. Temp 3Q Avg. RH 3Q Avg. Temp 4Q Avg. RH 4Q Avg. Temp Avg. RH
Kunming 50.7 63 65.3 68.3 66.2 82.3 53.1 76.3 58.83 72.48
Jinghong City 69.1 66 79.8 72 79.5 82 70.4 80 74.70 75.00
Hong Kong 63.3 78.7 77.8 82.7 83.1 80 71.1 71 73.83 78.10
Kuala Lumpur 82.7 80 82.7 81 82.6 79.7 82 83 82.50 80.93
Seattle 44 75.6 53.3 69.1 63 62.3 47 79.5 51.83 71.63
New York 37 60.1 61.7 61.1 73.3 66 51 64.8 55.75 63.00
Las Vegas 53 39.3 76.3 20.9 88.3 23.9 57 37 68.65 30.28
Miami 69.1 71 78.1 71.7 83.1 76.3 74.5 73.7 76.20 73.18

Concept: Hotter Weather Holds More Relative Humidity

70RH @65F !=  70RH @45F != 70RH @85F. If you held the RH constant for a few years, the tea stored at 85F would be the furthest along. One reason for this is that hotter air holds more moisture and even though they all have the same relative humidity, the temperature difference means that there is much more water in the air at a higher temperature. This helps to explain how the hotter weather in Hong Kong would age tea more quickly than Kunming even if they had somewhat close relative humidity values.

  • I’ve seen someone argue that we shouldn’t even bother with relative humidity and instead just focus on the absolute humidity. This idea has merits but unfortunately absolute humidity calculations involves more variables, including the barometric pressure. With this, comes the additional variable of pressure which has a strong relationship with altitude.. Pu’erh storage gets complicated quickly!

Long-Term Outdoor Storage in the West is Very Risky

I personally believe that most long-term natural outdoor or quasi-outdoor storage (i.e. shed, cave, the cellar, or even a natural warehouse) in the west is risky at best.. Even if you’re willing to babysit your tea for 20+ years, I think it’s probably a pretty bad idea. There are very obvious concerns… How to make sure the tea never gets moisture from rain or condensation? What about insects and pests? What about smells and aromas? All of these are potentially stash-ruining scenarios but also are plausible. I’ve heard multiple instances of tea stashes being consumed by rats, even one instance where it happened indoors!

Even if you feel safe answering these basic questions the natural conditions outside may not be great… If we look at the most extreme average monthly low and most extreme average monthly high we can take that as a range of conditions the tea will be exposed to. If we take a look at a few Asian cities — in Taipei the temperature shifts from around 57F (78RH) and 94F (73RH). Hong Kong’s statistics read similarly. Further south, Kuala Lumpur (Malaysia) is known to have very little seasonal changes and shifts between 74F (80RH) and 92F (82RH) throughout the year, a very limited range.

The west is big, but if we crunched these same numbers for a few places around the US, it’s easy to find a pretty big range of conditions. In Seattle a place known for a moderate climate, it shifts from 42F (78RH) and 76F (65RH), Boston goes from 29F (62R) and 81F (70RH). What about somewhere higher elevation? This can mean that throughout the 24 hour day there is an even bigger swing. Denver, the mile high city, for instance has a huge range between 17F (55RH) and 89F (48RH).

With natural outdoor storage you are working with a variety of conditions many of which are quite different from the natural conditions in east Asia. Storing pu’erh outdoors means you have to account for all of these conditions, both the coldest, the hottest, the most humid times of year and the times when the conditions change rapidly. The natural conditions for certain western locations may look pretty good in the summer but the lower temperatures in the winter are highly concerning.. Much of the west has significantly cooler weather than Taipei, Hong Kong, or Kuala Lumpur where the lows bottom out between the high 50s-60s…

Temperature & Humidity Range of Cities. The Highest Monthly High & Lowest Monthly Low Temperatures of Cities

Temperature Low Temperature High Temperature Range RH Low RH High Range
Hong Kong 58.1 88.5 30.4 69 83 14
Taipei 66.4 93.7 27.3 73 80.6 7.6
Kuala Lumpur 74.1 91.6 17.5 79 84 5
Kunming 38.3 78.5 40.2 60 81 21
Seattle 35.6 76.3 40.7 65.4 80.1 14.7
Boston 22.2 81.4 59.2 62.3 71.8 9.5
Denver 17.1 89.4 72.3 47.8 56.6 8.8
Miami 59.9 91 31.1 67.3 77.8 10.5

Following this idea — pu’erh folk should also be careful about going out of town for an extended time when the weather is extreme and leaving your pu’erh unheated (i.e. you live in Chicago and go out of town for two months when the average temperature is -6C). Devices that are more insulated, such as a mini-fridge or a wine cooler can help somewhat to protect against this. That all being said, pu’erh is pretty robust and doesn’t go bad overnight… Still for those with a significant amount of money invested I’d be erring on the side of caution and perhaps leaving the heater on to at least 50-55F while vacationing.

  • There’s one particularly famous instance of outdoor storage in the US done by David Lee Hoffman. He’s notoriously private about his storage and if there were any issues we’d be unlikely to know. Hoffman’s cave is notably located in Marin County, California where conditions are relatively mild and rarely go beneath freezing, ranging from ~40-80F throughout the year. Having tried a few teas from his cave, I also can’t say I found the storage to be anything inspiring.
  • In the above data, you can also note Kunming differs from places like Kuala Lumpur or Taipei. Kunming has a bigger and much colder temperature range — conditions quite similar to Seattle.

Indoor Storage

Storing your pu’erh indoors, limits the range of temperatures and conditions your tea is exposed to. Rather than worrying about tea at both 25F and 85F, you need to be concerned with what it is in your house, likely 60-75F.

While this is comforting, indoor storage brings up other issues. When the weather is extreme outside, most houses will use heating and/or air conditioning. The tea isn’t exposed to the extreme outdoor conditions, but the heating/AC both dry out the air and drive the relative humidity down. In practical terms, if you are storing your tea indoors you’re working with very different parameters than the climate data which measures outdoor conditions. It might be 40F and 90RH (as it is now in Seattle), but indoors it is 70F and 45RH. Those are two vastly different conditions that will age pu’erh very differently..

Even when we are not using either the AC or heating your conditions are probably pretty different from outside. We also all have different living conditions from each other. For those storing tea you should buy a cheap hygrometer and take measurements of the ambient temperature and humidity within your living space. Your own measurements are likely to be far more meaningful and practical than reading the outdoor climate data of your space.


Pumidors are essentially the indoors within the actual indoors and help to reduce the range of conditions even further.. I use the term pumidor loosely, including all kinds of devices (fridge, wine cooler, plastic bin, etc.). Because the indoor conditions are usually too dry, most people use the pumidor to attempt to tweak humidity upwards, most commonly with a glass of water, humidity beads, or Boveda packs. There are some people doing some interesting experimentation with heated storage, but that is beyond the scope of this post.

Pu’erh itself holds water and generates humidity when put into a confined space. If you had an empty ziploc and the measured real humidity when sealed was 45RH.. If you then did the same measurement but with a ziploc with a 72RH Boveda pack (designed to settle at 72RH) allowing time for it to settle, the reading should be around 72RH. Now if you did the same thing but with a cake, the reading would likely read much higher, potentially around ~60-65RH. Even if you were to not add any extra humidity with Boveda packs, simply containing all of your pu’erh into a relatively confined space should help to raise the RH (if drier western conditions are assumed).

Outdoor vs. Indoor vs. Pumidor Conditions in Seattle.

My approximate conditions. Outdoor vs. Indoor vs. Pumidor Conditions in Seattle.

This entry was posted in Aged Pu'erh, Article, Raw Pu'erh, Ripe Pu'erh, Storage. Bookmark the permalink.

14 Responses to Outdoor & Indoor Pu’erh Storage in the West. Why Climate Data Only Tells a Partial Picture for Home Storage.

  1. Cwyn says:

    What a great post!

    Sometimes the temp extremes and then taking the average for the month, as the weatherman on TV likes to do, is not very helpful. We will get two weeks of well below zero temps and a couple of freak warm days in January. The two extremes will lead the weatherman to say “see? Our month was average!” No, it really wasn’t, it’s just a math number and my puerh is gonna curl up and die if I don’t create a microclimate for it to protect from those extremes.

  2. Scott Wilson says:

    Very interesting… although Jinghong stored pu-erh is much more wet storage feeling than Kunming. Maybe that 2.5% average RH% makes a big difference beyond a certain threshold?

    • Karl says:

      I suspect it might have more to do with the higher temperatures than the RH since they are so close

      • Scott Wilson says:

        Yes… and Jinghong is also higher humidity as well.

        • James says:

          Thanks for chiming in Scott & Karl.

          Yeah. I think Kunming vs. Jinghong is a pretty interesting comparison.. I agree that the tea I’ve had from Jinghong definitely tastes much further along/wetter than most Kunming stored tea.

          My interpretation from afar is similar to Karl’s that the temperature may have a pretty big impact. The higher temperature should mean that the air is holding more moisture.

  3. MattCha says:


    I think too much time is spent trying to figure out temperature and humidity and not enough about the probacteria and maintaince and protection of that micro climate.

    Give it a few years and most people will be wrapping their puerh tight to try to maintain the balance of those colonies. Pumidors do a poor job of this, I think.


    • Jonny山内 says:

      I think you have a very good point.Well put.
      Perhaps we may also come full circle where we trust our own sense of smell and taste and sight over a range of parameters dictated by humidity and temperature sensors. Granted, the science bit is always appreciated but the constant evaluation of your stash through your nose,eyes and mouth us far more enjoyable and probably more accurate.

    • James says:

      Hi Matt,

      Thanks for the comment.

      I do agree that bacteria is fundamentally important in pu’erhs aging process Respectfully, I am a little dubious of the argument that pumidors are that fundamentally different in terms of bacteria than other storages. Things like sealed storage (very little airflow) or a more open air/cardboard setup (more airflow) seem to be at more extremes than a storage with a bunch of cakes stored together in an enclosed space (a pumidor).

      But until people start taking bacterial samples of their tea at different points with different storages, there’s not much evidence for or against it. I’d certainly be curious if anyone took that extra step.

      As far as temperature and humidity. They’re easy to measure and I think they’re pretty important for approximating things like the speed at which something ages or if it will mold, etc.


  4. MattCha says:


    I never really thought of a pumidor as The Middle Way of puerh storage but if you use open air vs sealed storage as comparisons then I guess it is… hahahs

    I liked this article and your other linked article on storage because it reminds us that we are not storing puerh in an ideal situation and each of our situations is different. It’s also amazing how resilient puerh is in any storage situation. It can be revived from even the worst storage!

    I agree with what you are saying, however, none of this matters too much if you seal the puerh.


    • James says:

      Hi Matt,

      I guess we’ll find out eventually! I’ve heard of many different pumidor environments, so I suspect we’ll be dealing with some pretty interesting results down the line.


    • Cwyn says:

      mold is probably the more common concern, as opposed to bacteria which is more of an issue in shou fermentation (if it’s an issue at all, since it will die off over the years). Taking samples probably would just lead to more confusion and panic among people at what might be more of a regular fluctuation. We do know that bacteria in sheng and shou have been compared scientifically and both types of tea will see bacteria decline as the tea finishes its fermentation cycle and they do so equal to one another. Bottom line is rinse the tea in boiling water and discard that first wash.

      Here is a source to consider on these topics: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4918958/

  5. Gonzi says:

    Congratulations on your website; it is nice to see some westerners appreciating and promoting the tea lifestyle, especially young people 😉
    Some good points above from MattCha.
    Before getting into too much discussion about the various parameters, you have to be clear what you are trying to achieve in your tea storage. Are you trying to protect your tea from mould or drying out or are you trying to replicate the wet storage conditions of southeast asia which led to the introduction of the ripe tea processing the in 1970s?
    Replicating the wet storage conditions requires a somewhat sophisticated approach that will assure constant temp and humidity otherwise, you risk too much moulding out your tea. This can be achieved with a small insulated inclosure such as a mini fridge, but you must have some air circulation since stagnant environment will lead to non-favourable conditions at the tea air interface which is the only area that matters in your pumidor. The tea does no “see” all the air in the storage space. It can only exchange heat and humidity with the air which is in direct contact with its surface. The reason you think it is better to have a full storage space with lots of tea is not the amount of tea, but the small volume of air. In this case, the measurements you take in the air are more representative of the air at the interface and the tea is controlling the environment. If you put one cake in a large volume of air, the air is controlling the environment. This is when a change of temperature will be detrimental to your tea since the large volume of air will greatly affect the surface of your tea.
    To get back to tea storage. Ripe tea does not need to be in any special environment. Once the ripe tea has been properly aired out after production, which any reputable tea maker would not release to the market before it has been, you should keep it in a sealed bag and drink it in the next few years (basically yrs 2-5). No point in keeping a ripe tea longer than 5 yrs since further changes will be extremely small and if you don’t seal it, it will most likely deteriorate in quality since all tea eventually lose moisture. The whole reason the ripe tea process was invented was to avoid having to age the tea and make it ready to drink.
    For sheng type teas, if you are interested in dry storage, such as practiced in the tea storage areas of Yunnan, humidity will accelerate the aging process but temperature is most likely the determining factor. Even without a lot of data on Pu’er tea microbial activity, it is scientifically intuitive that microbial activity would predominantly increase or slow down with temperature as the main factor.
    For 99% of tea buyers, a simple storage enclosure in your home, away from heat source or potential smells (kitchen, wood stove,…), and which you can keep between 50F-80F & RH40-70 is ideal. The lower range of these conditions will slow the aging process but only slightly. The disaster scenario is to try and push the conditions of heat and humidity and ruining the pure taste of your tea with mouldy flavour. Extreme yearly conditions of dryness or high humidity can easily be controlled by sealing your tea. This way, the tea is safe and happy in its own microclimate. Nowadays, most reputable tea producers provide resealable storage bags for their teas and also ship the teas sealed in plastics pouches to avoid customer carelessness with tea storage and protect the tea flavour they have worked so hard to achieve.
    So yes, sealing your tea is probably the easiest and safest method if you have any tea worth aging.

    • James says:

      Hi Gonzi,

      Thanks for the comment. I’ll say a few points here..

      (1) While I can’t speak for everyone.. I think most westerners storing pu’erh probably aren’t storing for the long haul. This post isn’t intended to address that case (store it away from smells in a ziploc or something). I think those who are storing it more long-term are essential trying to preserve, age and improve their tea while avoiding mold. There’s a few special cases, but I don’t believe there’s many people that are actively trying to achieve a “wet storage condition”. I also think most people that read this site are storing far more raw pu’erh than ripe.

      (2) I’ve stored tea in more or less the same environment for about four years now. While there’s a chance, that I’m missing something.. When I taste these teas I can’t detect anything very obviously wrong with it. The tea to me seems to be far more close to something akin to Kunming dry, the tea is aging but slowly.. There’s not much indication that it is even at Guangzhou/HK/TW dry storage levels..

      This makes me a skeptic of the importance of airflow. Perhaps in more aggressive conditions it is necessary but I’ve never felt the need to add a fan or anything like that. It also makes me skeptical as to how tea will age when it is stored in the lower rungs of conditions you outline (50F-80F, 40-70RH). If my tea is stored in the higher rungs of those conditions, it seems like at lower parameters the tea wouldn’t really be aging, and at best would be stuck in stasis.

      (3) Tea/air interface. I’m not really sure I understand what you’re saying, but I’ll refer you to: http://mgualt.com/tealog/2017/12/14/conditioning-experiment/ . I think there’s some evidence that you can think of cakes as similar to Boveda. The experiment shows a more controlled environment than a pumidor.

      (4) In the end, I am more comfortable storing the tea the way I do because I believe that it is closer to creating the conditions of well-stored tea than storing the tea in cardboard or simply shrink wrapping all my tea. As a final note that sealing has a range of setups and there are some setups that I am more optimistic about.. For instance, there are some people that are experimenting with sealing teas with controlled temperature/humidity that I’ve been following with great curiosity.


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