Compressor cheese caves and humidity trouble!

[Knargle]

Hello!

I have a tall compressor-cooled refrigerator with an external hygro/thermostat for controlling the temperature and humidity.

The thermostat side of things works a treat - no trouble there. My issue is with controlling humidity.

Where I am, it's currently 30C and 50-70% humidity, so the fridge is probably running for about five minutes every five minutes or so, to maintain 13C. What I find is that when the fridge is running, the humidity sharply drops to about 75%, and when it's not, the humidity sharply rises to about 99.9%. I understand that this is down to condensation and dew points, but I need to figure out a way of avoiding it and maintaining about 90% humidity without these big swings.

Another issue I have with humidity is that I have three digital hygrometers, and at any one point I tend to be shown e.g. 75%, 85% and 95% humidity. They give my wildly different readings, and I have no idea which to rely on. The hygrostat itself is the reading that swings regularly from 99.9% to 75%. The other two tend to hang around 75% and 85%.

So a few questions at once:

1) how can I determine which hygrometer is most accurate?
2) how can I keep the humidity from swinging wildly downwards every time the compressor runs? (I do have the hygrostat hooked up to an ultrasonic humidifier, for whenever humidity drops below 90%, but it doesn't seem to have any effect on the depth of the swings.)

Any help or personal experiences most welcome!

[TravisNTexas]

You can check your hygrometers easily using a salt solution.  Put all three of them in an airtight container that you can see into without opening.  Put in a small container with table salt.  Add water to the salt to just dampen the salt.  You don't want to disolve it.  Wet salt in a sealed container will stabilize at 75% humidity.  So wait a while and check your readings noting the differences from 75%.  Hopefully one of them is accurate.  Some can be calibrated.

[scasnerkay]

I think you may get different readings on the hygrometers if they are in different positions in the unit. Are they next to each other, or at different heights in the fridge?
Mine measure differently based on where they are positioned, so I take the average as fairly close.
My humidity unit from perfectcheese.com (no longer made) registers larger swings in humidity than the small hygrometers.
Indeed, every time the compressor goes on, the humidity drops significantly. But I think the sensor is more sensitive than the hygrometers I have.
And the humidity comes back up pretty fast.

I tend to look at the averages, and not worry too much. I also look at the cheeses to see they are not cracking, and to check what is growing on them.

In the summer time, when the unit is running more often, I use smaller chambers around the cheeses to increase the local humidity.
In the winter time, when the unit is rarely cooling, I have to put in canisters to remove humidity!! And I hover around 95% regardless, so I get lots of surface growth!!

Good cheeses regardless, but it does mean I have to figure out what to make at what time of year!!

[Andrew Marshallsay]

It seems to me that controlling humidity is perhaps the biggest challenge facing the cheesemaker.
I think that Travis' suggestion is the best bet for checking the calibration of your hygrometers.
My answer to variations in humidity is a home-made humidifier connected to a humidity controller. (I use a Rainbird brand unit bought through ebay.)
I also use aging boxes - plastic containers - as suggested by Susan. This allows me to age a variety of cheeses with different requirements. The other plus is that in our hot, dry summers here, the humidifier doesn't really cope.

[Knargle]

Thanks, everyone! Some useful stuff there. I'll check the hygrometers using the saturated salt method, and I suspect now that the hygrometer that registers the big swings is simply the most accurate (the other two are pretty static), and not the most broken!

It's particularly hot here right now, so I think the little humidifier I have in there just doesn't do a good enough job humidifying when the unit is running. I think I'll fork out for a better humidifier.