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Fluctuating temperature and humidity - is it a big problem?

post #1 of 4
Thread Starter 

Hi all,


I am new to this forum and hoping to pick your brain on a problem of mine :biggrin:


I have just set up my first curing chamber made from a wine fridge with a small desk fan and humidifier at the bottom. I am still waiting for my humidity controller to arrive, however in the meantime I have had the fridge running for a couple of days and noticed the temperature and humidity is fluctuating a fair bit.


To get some data I have written down the temperature and RH every 15 minutes for 3 hours and the starting temperature/RH in the chamber is 13.7C/87%. The fridge cycles once it reaches 14.5C at which point it will cycle for about 20 minutes during which the temp will slowly drop to around 9.7C/41% RH and turn off. Shortly after it turns off the temperature and RH will slowly rise to 14.5C / 80-85%. 


Basically every hour it will go from 14.5C to 9.5C and back to 14.5C, while the RH will go 85% to 41% to 85%. The humidity increases quite fast once the fridge switches off whilst the temperature is a bit slower. I could turn on the humidifier to counter the fridge cycle so the RH doesn't drop as much however this will cause the RH to go through the rough as soon as the fridge cycle stops.


Over 3 hours the data is as follows:


Max temperature: 14.5C
Min temperature: 9.7C
Average temperature: 10.8C


Max RH: 87%
Min RH: 41%
Average RH: 67%


Note for this test the fridge has been on the lowest possible setting and the desk fan is turned on the whole time for circulation but the humidifier has been off the whole time.


The question: do you think this is cause for concern or is it okay as long as the average temp/RH are approx.. within the recommended? At this stage I will only be making cured meats. E.g. guanciale, bacon and maybe a coppa or bresaola but at some stage I would like to venture into sausage making.


Looking forward to hearing from you.



post #2 of 4

I have not found fluctuation a problem as long as average over 1 hour is good.  I'm seeing +-15% on RH with my setup.  Temp seems easier to keep tight, but still +-5 degrees.  My averages are where i want the target RH and Temp to be.

post #3 of 4

Hi Kasper


Can you post up some photos of your fridge setup as it will give us a better idea. Do you have a good air flow through the cabinet? This is as important as the humidity and the temperature. What you are trying to emulate here is a cellar or a cave where there is plenty of air space to buffer the moisture coming out of the curing meat. In a very confined space like a fridge small changes in temperature and moisture will create quite large effects on the humidity.


You may like to look at the following thread as I think this may be similar to your setup.



One thing we found was that the fridge thermostat was not sensitive enough to keep within the required range (as you have found) and so we ended up using a separate temperature and humidity controller PID. When the unit went over temperature the controller applied power to the fridge (with the internal thermostat set to maximum) and so this bypassed the internal thermostat. If it went below the minimum temperature it powered up a small reptile heater in the bottom of the fridge.





The humidity inside was provided by bowl of water placed in the bottom of the unit. If the humidity reached the maximum required a small (variable speed) fan attached to the side of the fridge was switched on to draw air through the unit. We found though that just having a bowl of water was not sufficient to get up to the humidity needed and so we dipped a small towel in the bowl (last photo) to give a greater surface area for the water to evapourate. This can be replaced by an ultrasonic mister.


The relatively small variations in temperature that you are seeing will not be a problem but the humidity changes mat cause it to dry a little faster than you need. It should not be a major issue though.

post #4 of 4

Controlling the humidity with precision in a small fridge--like a dorm-style fridge--is very hard because you are dealing with a relatively small volume of air, and the cooling elements are generally exposed directly in the chamber itself.


I am new-ish to dry curing, and to start I constructed a curing chamber out of an old 2.7 cubic ft. dorm fridge.  I use an Arduino microcontroller that monitors temp and humidity every minute, and switches on the fridge and a small ultrasonic humidifier as needed to keep both parameters within a certain range.  It logs to an SD card, too, so I have all the data available later for analysis (yeah, my geekish side).


What's clear is exactly what you observed--whenever the fridge turns on to cool down, the humidity drastically drops.  This makes sense as the moisture is quickly drawn to the cooling element which is directly exposed within the chamber (think of bringing a cold soda can outside on a humid day--it quickly gets covered with condensation).  This is easy enough to fix--just switch on the ultrasonic humidifier until the humidity gets back up to an appropriate level.  But as the fridge temperature slowly rises, the relative humidity does, too, until the fridge switches on, and cycle repeats itself once again.  You saw the same thing with the 15-minute manual readings with your set up.


Here's a more detailed view of what is happening in my setup.  The plot below shows 12 hours of minute-by-minute data.  Temp (°C) is shown by the thin blue line with the thick blue line representing the average, and uses the left-side vertical scale.  Relative humidity is the same, but in orange, and using the right-side vertical scale.  Even though there are relatively large variations in the relative humidity, the overall average is 86% (according to the temp-humidity sensor I'm using), and that's fine, as far as I can tell!


I have a pair of Spanish-style lomo embuchados curing now (my first product with the chamber...), and after 22 days they have lost 35-37% of their weight with a nice, decay-style curve.  They look great (and smell great, too!), and are almost ready to go.  So I am concluding that as long as the average temp and humidity stay in the right range, I think your products will turn out fine.

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