A Tea Addict's Journal

Temperature, humidity, and storage

August 30, 2013 · 14 Comments

I just got back from Southern Germany, where the land is flat and the beer is good. The weather was beautiful. I also came back with chapped lips, which led me to think about storing puerh tea in these places.

There’s a general consensus that the higher the temperature and the humidity the tea is stored in, the faster the tea changes. People disagree as to whether that’s a good thing or not, and some of it comes down to personal tastes (some people like their tea young tasting for reasons I don’t understand). Above a certain point, the high temperature and humidity will induce mold, which is generally seen as less desirable this day and age. However, under normal circumstances in natural settings, it is difficult to generate enough moisture to attain the level of humidity and temperature used in traditional storage facilities (we are talking +30C and relative humidity of 90% or even higher, in a tightly packed enclosed space). If you store your tea naturally, in an environment in which human beings are comfortable and not exposed to the elements, your worry shouldn’t be mold.

Instead, I think the worry should be too low a temperature/humidity. The problem, at least on an anecdotal level for me, is that tea stored too dry will begin to exhibit undesirable traits such as roughness, thinness, and lack of aroma, in addition to just not changing (or changing very slowly). I am presuming that the whole point of storing your tea is that it changes and ages – for those who want their tea young and fresh, you can stop reading now.

The dryness-induced changes are usually not very obvious problems, and may not even be apparent until you tried it side by side with a tea stored in a more optimal environment, at which point it becomes really clear that the tea stored in really dry climates is lacking something. Opinions are mixed on whether that can be revived, but it’s not at all clear that it is easy to do so without running risks.

Leaving aside why exactly higher temperature and humidity seems to allow teas to age in a more interesting manner, I suspect that it is not as simple as pointing to your humidity gauge and saying humidity is high in you neighbourhood. Since both of these factors are actually related to one another, I will attempt to talk about this in more absolute terms.

Hot air can hold more moisture than cold air. That’s just a matter of fact. Relative humidity in general is a poor indication of the amount of moisture in the air at any given time, unless you also give a temperature reading. So, if you look at this chart, you’ll see that at 30 degrees Celcius and 50% relative humidity, the air still has more moisture in it than 15 degree Celcius and 100% relative humidity. At the same time though, we know that the air has more capacity to suck in moisture – so it can dry things out faster. Experienced hands here who have long stored tea all believe that it is important for the tea to breath through the seasons – meaning that it goes through wet and dry periods. The winter, when it’s dry and cold (relatively) here, is when the tea rests. Then spring comes, when it’s quite wet, and then the summer, when it’s hot, and by the fall, it starts drying out again. And the cycle repeats itself. Slow changes in the climate seems to beget changes in taste.

I remember when I came back to Hong Kong one time during my study overseas, I noticed that one of my tongs of tea was moved to closer to the window, and this being early spring, it was extremely wet and warm in Hong Kong. The tong was almost wet to the touch – the tea, while not quite soaked, was certainly not dry. I moved it to a higher location on the shelves and, now, years later, the tea is no worse for wear, and in fact is quite nice last time I tried it. It has also certainly aged from when it was first purchased, when it was a green, young, rather bitter thing. That’s what we want after all – for that bitterness to recede and slowly replaced by aged tastes of sweetness.

So when I was in Germany, I noticed that the weather was quite warm, but it was very, very dry. It also gets cold rather quickly at night. Of course this is far from desert like climate, but it reminds me of Beijing, where the weather can also be pretty dry and warm. In my experience, places like that produce really badly stored cakes – they literally feel dry when you drink them, and are usually devoid of fragrance and flavour. Heat with too-low humidity is no good – the ones I’ve tried where they have been stored in high heat, low humidity places tend to be really, really nasty. When people use the term “dry storage” they really meant it in relation to “wet storage” or what I like to call traditional storage. It’s not “bone dry” storage. That’s what you do for mummies. I think the reason it’s dry during the day is because of the low temperatures at night, the moisture condenses, and over the course of the day as it heats up, the humidity drops because temperatures go up – and before there’s a real chance for the moisture to be evaporated again, temperature drops again at night, keeping things fairly dry during the day. I’m not sure what this does to tea, but I suspect it’s not a great environment.

Having said that, I generally think it’s not very wise to build elaborate pumidors to try to artificially inflate humidity for your storage. The reason is simple – it’s very risky, and you can easily cause mold or other undesirables. What you can probably do without much harm is to take precautions – don’t let too much airflow into your storage area, maybe add a little water container that has little risk of spillage. I really wouldn’t do more than that.

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14 responses so far ↓

  • MattCha // September 3, 2013 at 2:40 pm | Reply


    When reading this I felt you were the voice inside my head…. hahahah

    Have been thinking about this too much since the move to the Canadian prairies. Think I am leaning to a humidifier in the tea room. The central air system ensures circulation so we will see how that goes.

    Thanks again for the great article.


  • MattCha // September 4, 2013 at 12:28 pm | Reply

    They all say “It’s a dry heat” in the Summer.
    They all say “It’s a dry cold” in the Winter.
    See the common denominator?

  • Comprar té // September 10, 2013 at 10:42 am | Reply

    Hi MarshanIN, i need contact with you, i dont see email.

  • MarshalNo // October 8, 2013 at 11:22 am | Reply

    Hi MarshalN
    You are the GOD of tea. It is amazing that you can figure out all the ideals of tea by just thinking about it. Kowtow to u.

  • miig // December 31, 2013 at 5:23 pm | Reply

    Hello MarshaIN,
    thanks for this nice article and greetings from Southern Germany.
    It really is difficult to store PU here, and the facts you mentioned are exactly why I gave up on a real collection here – there propably just is no way to get this done really well.
    Especially here, guys love to construct elaborate machines, but besides the risques and costs of constructing a ‘Pumidor’, it also feels quite artificial to me to create a machine-maintained environment for such a natural product. So I’ll rather order more often, and for more a price, but get teas that have until then been stored in a good environment. Seems to be the logical thing to to.

    Many greetings, Michael ‘miig’

    • MarshalN // January 2, 2014 at 3:52 am | Reply

      You’re probably right, and I always think that while pumidors are fun and possibly useful, it is also very risky – I’ve met a number of people whose pumidors imploded on them (usually because of mold) and ruined teas.

      My experience with cold climates in general is that they don’t do that well – heat, it seems, is an important factor. It probably has to do with the absolute moisture content of the air in which the tea resides, not sure.

  • Larry // August 2, 2014 at 10:48 am | Reply

    North Texas good for aging?

  • Von Monstro // August 6, 2014 at 12:34 am | Reply

    I’ve got some cakes in Washington state; I have many thoughts about storage here. I’m curious as to how they’ll turn out. I’d think that with the climate of the Pacific Northwest, it’d be humid enough– maybe even too humid– but I’m not sure about the relative humidity in my home.

  • Dustin // August 10, 2014 at 12:35 am | Reply

    So, what are your thoughts on low temperature, high humidity storage? Here in Auckland, New Zealand, humidity rarely drops below 70% all year – and it hits the mid-nineties with some regularity. However, the temperature in Summer is generally quite moderate: 24-30˚C is about standard in the daytime; it rarely drops below 18˚C, even at night. Winters are very, very mild: daytime temperatures are around 10-14˚C – overnight frosts are rare, and nighttime temperatures are generally between 8-12˚C.
    So I’ve been thinking about this a bit recently, after I discovered a bit of mould growing on some of my ripe teas (and my small Xiaguan sheng collection!)… and it’s dawned on me that Auckland isn’t so much humid as it is damp. Now I’m becoming concerned for the long-term wellbeing of my teas.
    I suppose it doesn’t help that our current house has a mould/mildew problem already – and we can’t afford to get a dehumidifier at the moment.

    The mould on my teas is grey, with visible fruiting bodies, and quite sparsely spread out into little spots, mostly on stems. It’s definitely not a nice mould. I’m considering putting my ripe teas into quarantine for a while, and then putting all my “open-air” (pu’er) teas into a separate container to keep the damp out, just until I find a better solution.

    I’d love to eventually make a “pumidor”; however mine would be less to increase humidity and more to protect my teas from the natural climate here!

    • MarshalN // August 10, 2014 at 11:30 am | Reply

      IMO cold and humid is probably the worst combo – you run all the risks of mold without a lot of the benefits of it. At least cold and dry just means your tea is sort of frozen in time. If your tea is growing grey mold, I’d be pretty careful, and depending on what it is, may not be a good idea to drink. Long term dampness for tea is really not a good thing and home-grown mold without the professional control of a proper traditional storage facility (or experience) will result in just bad tea.

      Stems grow mold first, then on the leaves. If it’s only a tiny bit on stems, you’re probably still ok. You shouldn’t store your tea completely open air – putting them in boxes is probably a good idea, to shield them from the dampness, if nothing else. Find drier corners in your house for that. The few times I’ve discovered mold on my own tea is when they were exposed to the open air during damp weather.

  • ItsTrickey // December 29, 2015 at 8:41 am | Reply

    I live in Las Vegas, NV… one of the hottest, driest places in the US. I’ve learned firsthand that high heat and humidity will turn your tea into fungus amongus FAST. Once I had some in a clay jar with a cap n’ cotton ball soaked with water and it turned into a mold pile in a few weeks.

    The other method I’ve used is to put it in a bamboo rice cooker inside a cabinet with a bowl of water sitting next to it… it turned out dry as a bone.

    I have to be extremely careful about too much humidity or too little. I’m starting to think the only realistic way for me to age mine is to just make sure the cakes are nice, fresh & moist before putting them into sealed Ziploc Mylar bags. Then, monitoring them closely every few days to make sure they aren’t going to mold. Then opening them up and changing out the air in them every few months…

    Finally giving them some moisture in a sealed container like a tin or rubbermaid container a few times a year… in a COOL environment so they don’t turn to mold after a few days.

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