Issues Under-Shooting Ferm Temps w/ Probe In Wort (Temp Controlled Freezer)

[gifty74]

I have a chest freezer with Ranco digital temp controller. I have a Speidel fermenter with a thermowell that sticks down in the wort. The probe from my Ranco is a perfect fit and I push that all the way down to the bottom of the thermowell so it's pretty tight and I'm sure within +/- 1° of ferm temp.

The issue I'm writing about happened overnight last night. Have the controller set to 65F. It was at 66, so I left it overnight. This morning I checked and it was at 61F!! Not great. I guess what's happening is the freezer keeps running until it hit 65F, which probably took a while until the soak got into the interior of the fermenter and had an affect on the probe. By then the freezer was probably near 0F, and after it shut off the fermenter kept dropping in temp.

What is the solution to combat this? I think I might have had better control with the probe hanging in the air and assuming an 8F delta during active fermentation. Not sure I want to try and rig up a fan to circulate air. Any other ideas?

 

[BargainFittings]

The best method in my experience is to tape the probe to outside of the fermenter and cover it with a bit of bubble wrap to isolate it from the air. You get much less of overshoot than submerging the probe in a thermowell.

There have been multiple posts with testing of the different methods but I can't find one at the moment.

 

[Inkleg]

Sounds like you have a good understanding of why it's happening, but wouldn't change your probe placement. Sounds like you need is a heater to help maintain the temperature within a degree or two. Does the controller support a heater? I use a reptile heat tape in my fridge. Works great with the fridge at keeping steady wort temperatures. I have my probe in a thermowell in the wort too.

 

[laredo7mm]

The overshoot should settle down, but with a simple on/off controller that only has the adjustment for dead band, it will never be great. To control the temperature better, you will need to go to a more sophisticated controller. I use the BrewPi software running on a RaspberryPi with an Arduino to control the ferm chamber.

In the BrewPi settings there is a parameter you can set to limit the maximum deviation of the chamber temperature with respect to the beer set temperature. For example, if you have your beer set to maintain 65° and the beer is currently at 68° and the max differential set to 10° it will limit the chamber temperature to go no lower than 55°. This may take longer to chill the beer down to the set temp, but it helps control the overshoot when the chamber is working hard to chill the beer.