Humidity! Can someone explain it?
What humidity is and what is does especially with storing Pu-erh is known by the most of you I am sure but what I found really strange is the impact with the out- and the inside!
What I mean is: At the moment at our flat we only got 40% RH and outside it is raining according to the internet it got 82% RH – so for me it would be logical if I open the window also inside the humidity should increase but it is in fact the opposite. If I left the window open for a while it drops under 40% mostly around 36% or even less! But why?
You are probably getting a drop with your air moving around according to pressure. I would say if you opened windows on both sides of your house and put a fan in one window you may equalize it a bit.
You did not tell us the temperature inside your flat, or outside when you opened your windows. I think this is the missing factor.
where the rain clouds are located way up in the sky, its 100% RH in order for it to rain. The RH will be different down here on the ground even if the rain is falling.
The measuring device that recorded 82% RH was most likely at the weather station across town, perhaps miles from your flat. And perhaps that recording was not real time RH, but maybe forecast, or averaged, or from an hour or two ago.
Rain is water droplets (liquid) not water vapor (gas). Humidity is a measure of water vapor. So the rain falling will not necessarily increase humidity. My guess is that opening your window changed the temperature inside your flat, which changed the RH. You have to account for temperature.
Relative humidity shows the percentage of the maximum amount of moisture that the air can hold without condensing. The confusing part is that this amount of moisture is strongly dependent on temperature. So, for example, 50% humidity at 80 degrees will have more moisture than 100% at 40 degrees.
The way to compare is to convert to the dew point, which is the the temperature at which the given humidity level would equate to 100%. There are conversion programs available on-line; I have one on my phone.
What is implicit in the conversations about puerh and humidity is that the temperature in southeast asia, where most puerh is stored, is fairly warm, so the dew point will also be high. It is reasonable to assume that the temperature at which you want the humidity to be 60% (or whatever) should be 70 degrees or more. By the way, I suspect that long periods of cold storage would be as detrimental to the tea as long dry periods.
For starters you might want to read this post where I point out how meaningless it is to compare relative humidity when we should be talking about absolute humidity.
https://steepster.com/discuss/19694-humidity-relative-and-absolute-puerh-storage
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