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|
Concept: Hotter Weather Holds More (Absolute) 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|
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.
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).