It's hard to find a low-cost accurate instrument to measure relative humidity (RH). Some of the cheap ones still use horse-hair movements (not accurate). The good ones are expensive.
If you do a Google search on 'P3 International P0270 Mold Alert Electronic Thermo-Hygrometer ' you will find a good candidate for low-cost and accurate. I ordered one this morning from amazon.ca (out of stock) and will report back when I get it.
The relation to coffee? the company 'P3 International' is the same one that makes our Kill-A-Watt meter, which works, is well-made and is good value.
Not only is the PO270 sold by P3 International, of Kill-A-Watt fame and fortune, it also has a Swedish-made sensor.
Fifteen years ago, when I was controlling quality in an injection-moulding plant, we had a problem with a polystyrene bulk supplier which was caused by inadequate drying of the PS pellets. But how to measure that?
I eventually found a company called Vaisalla Oyj of Sweden who sold me a very fine relative humidity (RH) meter and advised me as follows: Open up a newly delivered drum of PS pellets, stick the probe in for five minutes and read the RH of the airspaces between the pellets. That will give you a comparative measure. If you have inventory of PS that work OK, use that as an initial standard.
It would not surprise me if the sensor is made by Vaisalla. If so, it is probably accurate.
Lurching back to coffee (as this is a coffee forum) those who wonder if their greens are coming in properly dried, here is the opportunity for more basic research: Get one of these P3 PO270 Thermo Hygrometers ($36). Get a Tupperware container. Fill it half-full of green coffee. Sit the PO270 on top and seal the container. Come back an hour later and read the RH and wet-bulb temperature of the airspace above the coffee.
Why am I even thinking about this? Because ...my current 10 lbs of Sumatra Mandheling is losing 18% in the roast. And I am paying (by the lb) for coffee plus included moisture.
The instrument itself, now hanging on my wall, seems to work well. The temperature reading is within 1F degree of my accurate Taylor thermometer. Right now, on a very hot day in Thornhill, Ontario Canada, where it is 93F and 37% RH outside, it is 77F, 47%RH and the T(wb) is 51F. My air-conditioning if fighting the 'good fight'.
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