Temperature Controller question

Hi guys,
I just got a Johnson Controls analog temperature controller. The manual says that there is a 4 degree window of operation. That way the refrigeration unit is not constantly cycling on and off. I have read that I should tape the probe next to the carboy, and even cover it with bubble wrap to insulate it. If I do this though won't it mean that my fermenting beer will also have a 4 degree variance in temp??If I set the temp at 68, the compressor will run until the temp goes down to 64? It just seems that a 4 degree swing is a lot. Please help me understand this...Thanks. Al

A 4 degree swing is not much for the ambient temperature of the fridge. The temperature of the fermenting wort would remain pretty constant due to its mass. Taping the probe to the carboy might affect it some, but I still think that even with insulation over the probe, the mass of 5 gallons will not swing 4 degrees. FWIW, I have my temperature probe in gel, in a yeast container suspended in the chamber. This seems to work pretty well with stabilizing the temperature. I previously just mounted the probe to the side of the refrigerator wall, but then I had to fine tune the control to get the fermenters at the right temperature. It seemed like the dial read around 56 F for the fermenters to be at 66-68 F.

Yes, sort of. Without doing some actual testing, I would guess that the outside of the fermenter (and the probe) will cool to 4 degrees below the set point and shut off, but it's likely that the main body of beer in the fermenter will react more slowly, so the temperature swing of the large volume of beer probably won't be as great.

I've experimented with various configurations and IMO the best way to set it up is to have the controller probe mounted in the air and not touching anything (particularly the evaporator coils). Use a separate thermometer attached to the side of the fermenter and covered with insulation. The heat radiating from the fermenter will be trapped by the insulation and the probe will be mostly isolated from the air temp. Monitor the thermometer temp and adjust the controller accordingly. Don't worry about what the actual set point on the controller is. I use an ordinary indoor/outdoor digital thermometer for this. They are cheap and sold everywhere. I've found them to be surprisingly accurate. If you are using a freezer, it helps tremendously to install a small fan (computer fan works well for this) to circulate the air. It also works best to run the fan continuously. Most refrigerators will already have a fan, but not all do. I can maintain my fermenter temps +/- about 1 degree F with this method.

Be aware that the temp of the fermenting wort is going to be higher than the air temp around the sensor, and set your control somewhat lower to account for this. Measurement of the actual wort temp by stick-on thermometer strip or remote thermometer is helpful.

HenryHill said:

Be aware that the temp of the fermenting wort is going to be higher than the air temp around the sensor, and set your control somewhat lower to account for this. Measurement of the actual wort temp by stick-on thermometer strip or remote thermometer is helpful.

Click to expand...

+1 This is true, but it's usually only an issue for the first few days when the fermentation can be vigorous and yes, the separate thermometer can give you a better approximation of the actual temperature in the fermenter. I like to lean toward the low end of the suggested temperature range initially and let the fermenter warm up as it finishes out. Unlike some, I'm an air lock bubble watcher. I don't like volcanic ferments. Slow and steady is my preference.