[tmaurer]

I have a Johnson digital temp controller for my refrigerator.  I plan on doing lagers soon, but I have a few questions.  Here is a question I asked on another forum.  I'd like all your opinions on it:

I bought a Johnson digital temperature controller. I think the differential adjustment is defaulted to +-3. My question is what do you have yours set to? I've read that the default setting will save your refrigerator from kicking on and off as much which will increase its life.

But when dealing with fermentation temperatures, wouldn't you want the differential set to one. I'm thinking the up and down temperature swings has to be hard on the yeast right? What are your thoughts?

I've heard from a few smart people that say it makes more sense to monitor the ambient air in the refrigeration while fermenting.  They say I should set the differential to +-5 and set the temperature to 45° F.  What are your thoughts on this?

[dak0415]

I have mine set to +-1 but the probe is either insulated from the ambient air and taped to the carboy, or it's in a thermowell inserted in the beer itself.  It will take a long while for the beer temp to change at 'fridge temps.  A small fan in the 'fridge, blowing on the carboy will help.

Dave

[tygo]

I have mine set at 1 and I drape the probe over the carboys.  It doesn't run continuously.  Just by kicking on once it goes a degree above my desired temp it drops the ambient temperature by maybe four degrees by the time it shuts off.  Then that slowly creeps back up until its time for another cycle.  According to the fermometer the beer is staying pretty much exactly where I intend it to be.

[lazydog79]

Ditto what everybody else has said.  I have mine set at 1 with the probe hanging close to the carboy.  I've got it set to 52 for a lager primary right now.  The freezer probably kicks for a minute or so once or twice every hour in my 70 degree basement. If you are worried about the fridge turning off and on a lot, use the Anti-short cycle (AsD) setting.  You can use this to set a minimum time between cycles.  I have mine set to 5 minutes, meaning after the freezer turns off, at least 5 minutes have to go by before it'll kick back on, regardless of temp.

[Hokerer]

Think of it this way - there's far more thermal mass in your wort than there is in the air inside the fridge.  More thermal mass means that it's harder to change its temperature.  If you measure the temperature of the wort (by either of the mentioned methods), you'll be measuring a temperature that swings very slowly.  These slow temperature swings act as a sort of natural "Anti short cycle" and your fridge won't be turning on and off too often.

[tmaurer]

Thanks everyone.  It's always nice to get good info from the folks on this forum.