The 70/70 Line & Projecting Pu’erh Storage

A few years ago I thought it’d be interesting to try mapping certain temperature and humidity conditions to approximate a certain area’s storage. For instance, if you could maintain conditions of 55-65F/65RH in a storage setup that might approximate somewhat close to average Kunming storage. 80-85F/65-70RH might be Kuala Lumpur. After banging my head and never really getting anywhere I decided that this was a doomed exercise (or at least beyond what I’m capable of). One reason why is that while location clearly matters in storage conditions, trying to translate outside weather conditions to actual storage conditions is not easy or straightforward. In the west people will sometimes get quite excited about storage and look at their climate data and try to extrapolate. I don’t think this is a totally useless exercise but it’s pretty difficult to know what to do with these numbers. This article explores some limitations but also what I think is a shortcut to approximating your natural conditions and how they stack up with places with an actual record of pu’erh storage.

Indoor Storage
Ambient conditions and pumidor conditions.

Inside Storage is Inherently Different. Situational Dependence

While ~85% of the US has air conditioning; I grew up and live in Seattle, the rare major city in the US where not having regular air conditioning is still the norm.  I’ve been regularly measuring the ambient temperature and humidity in the two apartments I’ve lived since getting into this hobby and pu’erh specifically (about 6 years total). The indoor temperatures vary according to season, but range from 65-75F for most of the year, spiking around 80-85F at its very hottest for short periods during the summer. My relative humidity inside is typically around 30-45RH.. While I use heat for the winter, you’d think during the 7-8 months where I’m not turning on the heat my inside conditions might somewhat track outside ones. But this is not the case… Even during Seattle’s driest months, the outside climate data is consistently higher than the humidity inside.

So how much can you draw from outside climate data? People’s ambient conditions differ and are likely more important. I have a few friends, also in Seattle, living near the water that have struggled with mold. If I were to measure the humidity in their homes, I’m sure it would be much higher than my condition. In past conversations with Glen of Crimson Lotus Tea, he’s noted that a vendor storing their tea in Kunming near the lake is quite a bit more humid than those further out. Assuming you are storing your tea inside, situational things having to do with your living conditions are also extremely important. Not all X location storage is created equal.

Approximate Seattle/My Conditions:

  • Seattle Winter, average temperature/humidity: 35-45F, 75-80RH.
  • Seattle Summer, average temperature/humidity: 55-75F, 65-70RH.
  • James’ Winter Ambient Living Conditions: 65-70F, 30-45RH.
  • James’ Summer Ambient Living Conditions: 70-75F, 30-45RH.
  • James’ Winter Storage in Practice: 65-70F, 65RH.
  • James’ Summer Storage in Practice: 70-75F, 65RH.

A Heuristic: 70/70 Line.. (& Natural Storage)

I don’t think you should totally disregard your local outside climate. On a basic level it sets the playing field for your storage. Whether you choose to throw that out and try to create a more closed system, might depend on what that field is.

Learning where a tea has been stored has and still is an important way to gauge storage. When we see a description from a vendor that says “Kunming dry storage”, that means something. “Hong Kong natural storage” or “Hong Kong Traditional Storage” both mean something else. One other aspect that’s been finally getting its due the past few years is the importance of temperature. It’s not enough to just say your climate is humid and your RH is 70. Temperature is too important to how tea ages to omit. It can also have an indirect impact.. If you are living in an area with low temperatures during parts of the year it might mean you run your heat more and it contribute to drying out your air.

Below is a table I created a few years ago with quarterly temperature and humidity levels. I’ve added Beijing and Taipei to this as well.

Quarterly & Annual Temperature & Humidity of Selected Cities

Avg. Temp 1QAvg. RH 1QAvg. Temp 2QAvg. RH 2QAvg. Temp 3QAvg. RH 3QAvg. Temp 4QAvg. RH 4QAvg. TempAvg. RH
Jinghong City69.16679.87279.58270.48074.7075.00
Hong Kong63.378.777.882.783.18071.17173.8378.10
Kuala Lumpur82.78082.78182.679.7828382.5080.93
New York3760.161.761.173.3665164.855.7563.00
Las Vegas5339.376.320.988.323.9573768.6530.28

One quick exercise I’ve done is separate these places that have a track record of tea storage into two buckets. Places that have a reputation for dry storage and places that have a reputation for less dry storage. There can be variation on a case by case basis, but I think this more or less represents specific locations storage reputation.


  • Kunming
  • Beijing

Less Dry

  • Taipei
  • Hong Kong
  • Kuala Lumpur
  • Jinghong

Now if we stare at our buckets and our table it’s pretty clear that places that cities with both an average high temperature and an average high humidity are the ones with a reputation for less dry storage. This isn’t random at all. If your temperature or humidity fall beneath that threshold, you’ll be much more likely to have slow aging. I’d like to suggest a heuristic for approximating climates without much or any storage history. If the outside annual average temperature and humidity of your location are both at or above 70 natural storage has a reasonably strong likelihood to mature the tea fairly quickly. If you like Kunming stored teas and your natural temperature and humidity are beneath the threshold but aren’t too low natural storage could be fine. But if you like your tea to age more quickly than you may end up fussing with a storage setup.

One Conditions Above 70, The Other Beneath 70

There are a few places that have one of the two conditions are around 70 or higher but not the other (high humidity & low temp, or low humidity & high temp). If we look at these, I think it’s pretty clear they fall into the drier bucket storage. Kunming has an average relative humidity of around 72.5, but the temperature falls way short of 70F. Because hot air can hold more water, there’s less moisture in the air than places that have both a high relative humidity and a high temperature.

This relationship between temperature and humidity is very important and including both is essential. If we only look at humidity, and look at Kunming (>70RH) we might be misled into thinking 70RH alone regardless of temperature is dry storage. There are also many places in the US that have an average RH of above 70, but because they are colder on average the conditions end up having much less water in the air than if the temperature were higher. Conversely, a place like Las Vegas with almost 70F weather on average but very low relative humidity, natural storage will almost certainly fall in the dry-stored spectrum and run the risk of drying out the tea.

Of the western locations, New York, Seattle, and Las Vegas don’t come close to hitting 70/70. But Miami does. While we don’t have very much of a storage track record for any of these US locations, this intuitively fits about what you might expect.

  • Of course there are all kinds of nuances beyond this. i.e. Location A doesn’t have centralized heating often, Location B doesn’t use AC. These are important of course but as a quick rule, I think 70/70 tends to work fairly well.

Quarterly and Month By Month

Taking a high-level view is OK, but we can also zoom a little closer and look at specific times of the year by looking at the temperature and humidity details by quarter or month.. Some of my tea friends in the east coast have noted that their tea seems to be the most aromatic and age the best during the hot and muggy summers. While on a year average, New York falls way short of 70/70 in both temperature and RH, for the third quarter of the year (July-September) it comes pretty close to meeting that benchmark (73.3F/66RH), than its overall average does, lining up with my friend’s intuition.

  • How many quarters do your outdoor conditions average out to above 70F/70RH? Which ones are closest?
  • How many months?

This 70/70 line is far from the ultimate way to measure wetness or dryness. As discussed earlier, there’s a good deal of situational dependence within one place that is worth thinking about and people’s conditions vary considerably. The line is intended to be a quick, simple way to gauge how natural conditions may measure up to places with a more established storage record.. For instance, I’ve traveled to Chiang Mai and was curious how its storage would compare. There isn’t a long storage history in Chiang Mai that I’m aware of, but temperature wise it is quite hot, but it is also inland and perhaps not as humid as other parts of southeast Asia. With an average temperature of 78.4F and an average RH of 71RH it easily clears the 70/70 line.

A few others… Miami (& much of Florida) are probably humid enough that you can store tea similarly to places like Taipei or Hong Kong. Seattle is drier and colder, moreso than Kunming. In fact, most every US location are far too cold compared with the “less dry” counterparts.

A handful of final quick bullet points.

  • The only place to fall into the 80/80 category on our list is the largest city in Malaysia, Kuala Lumpur.
  • The temperature and humidity have a relationship where they tend to be inversely correlated and will max out at different times of the day. The hotter it gets, the relative humidity will usually go down. And vice versa.
  • This is relevant for those going for natural storage methods. A pumidor or sealed storage setup will change the equation because you are manipulating the humidity and possibly the temperature. I AM DEFINITELY NOT RECOMMENDING YOU STORE YOUR TEA IN A PUMIDOR AT OR ABOVE 70/70.
  • There’s very few major cities in the US that actually cross the 70/70 threshold. A few major cities in the US beyond Florida that are very close to meeting 70/70 are Houston (69.9F/74.7RH), and New Orleans (69.7F/75.9RH).

7 responses to “The 70/70 Line & Projecting Pu’erh Storage”

  1. I am glad you have brought this up again as it is something that gets talked about a lot and something I guess will never be solved.

    I think its also worth pointing out, as you hinted from your discussion with Glen, that two different warehouses in Guangdong, even sitting next to each other can have varied conditions for tea storage. As you have said “not all storage is created equal”. I think therefore its important not to get hung up on exact parameters. If you know a tea is Kunming stored you will probably expect a certain quality coming out of it compared to Guangdong storage, but this is not always the case. Other descriptors used by vendors such as “basement” or “traditionally” stored tea whilst helping to define a certain quality do not guarantee either a wetter or drier outcome to the tea.
    Equally I feel that traditional storage often has a vast range, based on seasonal adjustments that is hard to compensate for if you are aiming for a hermetic environment such as in a pumidor.
    For this reason I continue to opt for open shelf storage for my own set up at home and just keep an eye on humidity and temperature daily.
    I aim to keep humidity 65-75% with 16-21 celcius, allowing for some seasonal variation.

    I think its fair to say that, as with Marco’s hot box storage experiment, its good to try out some different parameters and enjoy comparing the results. The table above provides some guidance on this, but you will probably never achieve the same level of results that is unique to location, location, location right down to the minutiae of the GPS location and environment the tea is stored in.

    Perhaps there is a future for chipping bings so we can feed data into their wrapper around their storage history. Can you imagine a set up where storage conditions are recorded and uploaded to the wrapper chip , this might the blow the whole discussion around storage out of the water!! The question remains who out of the big vendors will do this first???

  2. Kunming has an average relative humidity of around 72.5, but the temperature falls way short of 70F. Because hot air can hold more water, there’s less moisture in the air than places that have both a high relative humidity and a high temperature.

    There’s also the fact that chemistry of all kinds happens slower at lower temperatures. And whether it’s due to microbial metabolic activity or just the action of air and moisture on once-living material, the transformation of tea with age definitely is chemistry. I suspect that a lot of what we see in KM storage is “cool storage” as much as it is “dry.”

    • Could be. Most places in the US have a temperature issue rather than an actual humidity one.

      One point about natural home storage in a cooler place with centralized heating is that the temperature ends up being somewhat moderate at room temp but your humidity is significantly reduced (see my example). I know for my own tea this results in pretty dry-stored tea. If I were to naturally store the tea without using heat, it’d probably end up being a temperature issue rather than a humidity one. So I lean towards having both humidity and temperature at healthy levels is the key to natural storage (that isn’t too dry).

  3. Something that would really interest me is how the indoor conditions of those warehouses are. I understand that it might differ from warehouse to warehouse, but it would still be very interesting to compare them to the outside conditions. I have to say I know next to nothing about how those warehouses are built and how they are ventilated. You already mentioned that your inside temp and humidity vary quite abit from the ones outside. I expect the same to be the case for warehouses, of course they don’t have to bother too much with heating, but depending on how they are insulated and if they are ventilated or not this might be quite different from the values you get by looking up the average climate of Hong Kong for example… Would be really interesting if a vendor could share the indoor climate of one of the warehouses they use over a year.

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