Correcting Your Storage & Preventing Mold. What are Safe Parameters?

So you got mold? This is a real risk for anyone aging pu’erh, especially those with setups designed to add some form of humidity. After you deal with the immediate outbreak, you essentially have two options.

  1. Scrap your setup and find a new one.
  2. Tinker and mess with small things within your setup.

I think people often freak out and choose option 1, when option 2 will usually suffice. In some cases finding a new setup is justified. If your container holding pu’erh is leaching off aromas into the tea or if your container is susceptible to a spill risk, you’ll probably want to make significant changes..

But in many cases of mold the parameters have simply been tweaked too high, making option 2 much easier and preferable. There is a really big range of conditions between people with pumidor setups. The temperature and RH aren’t 100% controllable but the whole point of a pumidor or controlled setup is to be have some power to manipulate and control the setup. People will tune their pumidors to different parameters.  A few tweaks to your setup might be enough to make problematic storage much safer.


Pumidors Vary A Lot. 65RH ≠ 70RH.

One reason I lean skeptical towards blanket statements about pumidors being bad is it tends to be very anecdotally based. They know a person that got mold or a teashop owner in east Asia looked confused and said it was not a good idea.. In my opinion there are both bad examples and good examples of storage with pumidor.

Yes, a pumidor inherently adds risk. There have been cases of mold. And there will be cases of mold in the future. If you’ve chosen to age pu’erh in the west you are going to have to come to grips that there is a lot of uncertainty. There is no long track record of tea aging here. There is a significant chance that your tea will not age well or to your liking..

If you believe that tea drying out on our shelf or in a cardboard box is a significant risk (I do!) and have a fair amount of tea cakes, a pumidor is often the easiest option. Yes it is a very different home storage setup than those based in Taiwan, Hong Kong, or Malaysia… I live in Seattle a North American city known for its rain. The average relative humidity for the entire year is ~73RH, but still my indoor humidity is rarely above 50RH. Sometimes a pumidor or some sort of sealed storage are the only feasible options to raise the RH to even 60, a modest RH that’d fall squarely into the dry-storage category. We have different climates than Malaysia and potential solutions will also look different.

Pumidor includes a large range of setup. The specific setup and parameters matter a lot. We’ll know down the road a lot more about how fast tea has aged under certain conditions. Seemingly minor differences in storage may prove to make a significant difference when we bring our timescale up to several years. In other words, Johnny’s bin that’s kept at an ambient temperature in southern California and at 70RH may be surprisingly different than my storage in a Seattle mini-fridge that is centered around 65RH and my ambient temperature. Barring more dramatic negative changes we’re not likely to hear much about people’s storage until significant time has passed. Pu’erh aging is a slow, long game and people are still operating out of a lot of theory. A couple years of aging really doesn’t tell us much as to how the tea will be under conditions in 20 or more years. I’ve had my own setup for nearly five years and am still not 100% sure where to place it in the spectrum of aging..

Temperature Matters A Lot

Temperature tends to get overlooked and underrated as an aging parameter. Marco and his hotbox experiment are covering important ground in showing the importance of temperature for home storage. I’ve covered this before, but temperature is correlated with microbial activity. Don’t focus solely on humidity, make sure to consider temperature as well as temperature changes. If you have spent some time with the Dew Point Calculator, you’ll also know that temperature and humidity impact mold growth differently. Temperature changes can contribute to mold via condensation, but a constant high temperature at 65RH is theoretically very safe. You’re a lot safer at a high temperature, than a relatively high RH. Something like 75-100F/65RH is safe from mold growth, but 65F/75RH+ is not.

Odors Also Matter A Lot

This one seems very basic but is a real issue. I’ve tried decade old US-stored teas from half a dozen setups or so. Perhaps the most common error is them picking up some sort of odor.. Check for off-gassing in your fridge or bin. Get a second and third opinion. This is very important and can impact your tea permanently if you don’t catch it quickly.

Safe or Unsafe? Range of Parameters

There are two major risks.

  1. Your parameters (temperature and RH) fall into a mold risk category.
  2. Condensation. Temperature change downwards.

For risk 1, I recommend using the Dew Point Calculator to find out where your storage falls. Don’t just look at if it is a mold risk, but the degree of risk there is. Even if your storage veers a little over the mold line sporadically, your tea is very likely fine. Whereas if you are at parameters where you have “11 days to mold” you probably should consider airing your tea out and reducing your humidity. Here’s some basic guidelines..

  • 55-66RH – Safe across various room temperatures.
  • 67RH-72RH – May or may not be safe. Pu’erh is stored very regularly at these sorts of parameters in east Asia but if you’re going to do this for an enclosed space your risk is increased. Probably requires some monitoring.
  • 73RH+ Danger zone. Again, pu’erh is stored at these parameters quite often.. But it’s unclear how long tea can be stored at this humidity in a pumidor. Remember, vendor setups in east Asia are very different from home setups. 70RH vs. 75RH makes a large theoretical difference on how fast you’ll get mold. On the Dew Point Calculator this may be the difference of mold in half a year vs. one month. It also further emphasizes the need to have reasonably well calibrated hygrometers.

For risk 2, condensation occurs when there is a change in the ambient temperature downwards. This is a major risk during seasonal shifts that will hit specifically around the bottom and the edges of your pumidor first.

  • Certain cakes are also probably more prone to mold. I think this can be dependent on the amount of internal moisture within the cake. Teas with a lot of stems may pick up on moisture and mold a bit faster than other cakes.
  • One of the smart things about Marco’s hotbox storage is that the humidity is relatively low and definitely in a safe range. With a steady temperature it avoids any temperature change risk. In theory, this makes his storage very safe from mold.
Storage Parameters
Storage Parameters.


  1. How you add humidity. This is an important one.. There’s a lot of ways to add humidity. I originally added small cups of water at the bottom of it. After hearing a few instances of people getting mold in the water, I stopped. Pricier Boveda packs are a good substitute. They can be recharged and if humidity ever spikes too high they will start to absorb extra humidity to keep it down. Others use salt packs, terracotta pieces or humidity beads. I’m not well-versed in these, and don’t know their pros and cons as well.
  2. Keep cakes off the bottom and off the edges of the pumidor. This is to combat condensation which hits the edges of the your container. If you are worried about condensation specifically, this is a good, place to start.
  3. Trigger Points & Airflow. You may have some pretty precise parameters that you want to store tea at but unless you are obsessively controlling temperature and humidity, your tea’s parameters will realistically drift depending on the season and ambient conditions. To handle this, you want to have trigger points, or points at which you will do some action. For instance, if your tea falls beneath 62RH, you may renew the humidity source or add a boveda pack. Or if your tea gets beyond 72RH, you’ll air it out by opening the pumidor. Or if the ambient temperature has fallen maybe you air out your pumidor for a few hours. These trigger points are important to prevent mold. Airing out your tea is an easy and functional way to combat mold risks. If you ever think your conditions are too extreme, exposing it to a bit of air for a short period of time can work in your favor.
  4. Measure different parts of the pumidor. Depending on what you’re using it’s possible to have certain spots in a safe area and others in a more dangerous zone.

Keeping Humidity Lowish but Reasonable. Playing it Safe

Most of the talk in the west is on pumping up the humidity. To a certain degree, this is important.. We are for the most part combating dry conditions. But there’s not a lot of focus on the opposite. Perhaps we should be also talking more about the risks of pushing our tea into the 70+ RH range for extended periods of time. The dew point calculator mold risk points towards this sort of risk if your tea.

When choosing storage parameters, I’d personally rather lean on the sign of caution.. The worst case is quite bad and can result in throwing out a lot of tea.. I’d rather my tea be a little on the dry-end than totally ruined.

You may hear instances of people storing tea in 70-80s RH in east Asia and directly translate those to your home storage. I think this is a bad and risky idea.. It’s better to edge lower than parameters we may associate with Hong Kong or Guangzhou. Airflow is a highly polarizing topic, but by putting our pu’erh in a fairly confined space it traps the tea with more limited airflow, increasing mold risks. Unless you are deadset on replicating higher humidity, pumping up humidity to the 70s isn’t a safe idea for pumidor storage.

How I’m Storing (~4.5 Years)

I keep my tea in a mini-fridge, a wine cooler, and plastic bins. I use Bovedas to add humidity. My parameters:

  • Temperature ranges from about 68F-78F. It goes higher for maybe 7-10 days a year.
  • Humidity ranges from 60-68RH, usually centered around 65RH.

My trigger points:

  • If tea falls beneath 60RH, I’ll add more Boveda and recharge it. This happens maybe once or twice a year.
  • I’ve never had to act on my RH getting too high, but I’d probably start to worry if it stayed above 70RH for an extended amount of time.
  • If the ambient temperature changes significantly, I’ll watch the tea more closely and air it out by opening the door if I think it’s necessary.

I believe these parameters lie on the more conservative side of the spectrum and I’ve never had any mold outbreaks from my storage. It’s hard to say precisely how my tea will age in the long-run, but it seems to be relatively safe thus far. It is also not too much of a headache to take care of.

Next time you hear of mold infecting someone’s stash, don’t immediately freak out and check all your cakes. Listen to them explain their storage and figure out their important parameters. Assess what might’ve gone wrong and if it has any application at all to you and your tea.

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11 responses to “Correcting Your Storage & Preventing Mold. What are Safe Parameters?”

  1. James,

    Very interesting post. I just decided to set up my own pumidor and had many of these same thoughts about what seemed to have been current practice. In the 2016 Pumidor Survey, it is striking that a lot of set ups — being in the 70+ RH camp — were risking mold at just room temperature. With little attention paid to temperature and dew point (that is, until Marco’s post), I’m surprised that there haven’t been more cases of ruined tea. I think that a conservative approach is going to be the best bet for most people, so I’m glad that’s your recommendation too. I’ve read that cigar people typically stick to 70RH/70F, and even then there seems to be a growing number who are recommending 65RH because it’s so much safer. At 65RH/70F you have quite a bit of room for the RH and temperature to fluctuate without concern.

    As an aside: Have you found a good way to store samples in your pumidor? I’m still not sure how to store the 25g samples that I want to acclimate before drinking.


    • >Have you found a good way to store samples in your pumidor? I’m still not sure how to store the 25g samples that I want to acclimate before drinking.

      I’ve recently discovered that calligraphy-paper makes a great alternative to CLT’s paper sample packets. They have a paper smell for a couple of days when placed in my pumidor, but it seems to dissipate with a little time in the humidity, so I prep a bunch of them at once and only use them after they’ve lost the smell entirely. It makes for neat organisation of samples.

    • Thanks Peter. I appreciate the comment. I don’t have much experience storing samples in the pumidor (don’t have the space) although I do think it’s a good idea for short-term conditioning if you have the space. A few people just open the bags and put them in the fridge door (if you’re using a mini-fridge) and I suspect I’d do something similar.


  2. Hi James, something that bears mentioning on this subject is that if you find mold, it is imperative that you check *all* your cakes to the extent this is possible. Sometimes the cake you find isn’t the cake that’s worst-hit.

    I maintain that one of the best ways to control humidity is with saturated salt solutions (with or without sugar-doping as described at On its own, a simple saturated solution of NaCl will cause humidity to asymptotically-approach 75% (rather than the 100% of pure standing water), which is already significantly safer than the balancing act of water bowls and terracotta chips. With a decent amount of tea, the equilibrum humidity seems to stabilise around <70%, just like if you're using 74% Bovedas, but without the price-tag.

    • Hi Alex,

      Yes, agreed re: cakes. For people with especially stuffed storage, there’s probably some spots that are more humid than not.

      I think that is a good solution for DIYers or those trying to save a few bucks. For myself– the cost of Bovedas amounts to a bit less than $20/yearly for quite a few cakes so I’m happy to pay that price.



    In the afternoon, make two cups of tea with friends.
    Both teas are stored between 40% and 50% humidity.
    It can be said that the storage is extremely dry,
    Although the conversion will be slower,
    But the layering of the tea soup is very obvious.
    If you do not taste carefully,
    I mistakenly thought it was the top rock tea or frozen top oolong.
    Because the delicate rock bone fragrance is different from the general Pu’er.
    The only thing that is slightly better is ~
    The thickness and pectin of the tea soup,
    I believe this is the charm of the ancient tree Pu’er.
    Warehousing of tea,
    Just as important as cultivating a child,
    If you want to be more fragrant,
    Believe in “storage conditions”
    Will be a university question.

    Thought it was interesting that Tony Chen would think that 40-50% humidity has advantages…

    • Hi shah8,

      Thanks for sharing. I’ve seen a couple somewhat similar anecdotes from Taiwan.

      My own experiences storing semi-openly in a shelf or in a cardboard box have seemed to work in the reverse direction, with the aroma slowly diminishing from the tea.. The living areas here are often a bit lower than 40%RH so maybe that is the difference. Temperature may be an additional factor. As a result, I’m quite a bit more comfortable storing it with a bit extra humidity.


      • The usual reason for loss of aroma, beyond what age does, is excessive airflow.

        And yes, if you bag teas or othewise keep them in airtight spaces, you’ll keep a strong aroma, at a price. In general, aging will weaken the original aroma. The best compromise is to tightly compress the cake.

    • I’ve only tried a small amount of heicha and some shengs in small crocks but it’s not set up for aging. I only use those to store a certain amount of tea so I do not have to pry of the cake every time. If I leave it for a few months the aroma does seem to get a little less but that’s okay with the bitter sheng I’ve, it seems to taste a bit less bitter and more easy to drink.

      It would seem that not much people tried crocks or you are perhaps better off asking Cwyn about it.

  4. I have 2 three gallon crock pots, one for sheng and one for ripes. This works for me in an environment with low humidity.

    Inside the crocks temperature ranges from about 68F-78F, highest in the winter because of radiant floor heat. Humidity ranges from 60-68RH.

    I use a 65% 60 gram Boveda pack in each crock and cover with clear wrap so I can read the hygrometers easily. I open the crocks to move the tea around and check the boveda packs every couple of weeks.

    The tea seems happy enough. Leaf I break off and set aside for easy access goes into a container with a small 65% 8 gram Boveda.

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