Fermentation - temperature differential

I acquired a wine fridge large enough to hold a 6.5 gallon carboy. I added a dual stage thermostat, plugging the fridge into the cold outlet and a seed germination pad to the hot. The pad is taped to the carboy like the Fermwrap (but this is only 17W). It seems to work nicely.

I first tested out the system without the carboy, just measuring the ambient temperature, but the temperature swing was kinda crazy. It would hit the max temp and start to cool. It would then hit the target temp, but the ambient air was still quite cool and the temperature reading would keep dropping, to the point at which it hits its minimum. So, it would cycle cold and hot every 5 minutes or so (pretty bad). I had the differential set to +-1.0C. So I finally tried with the carboy and attached the probe to the carboy. The probe is insulated along with a digital temperature recorder (USB). It's working very well. I will post graphs showing the stability soon.

QUESTION: What should the temperature differential on the thermostat be? I have it set now to only +-0.6 C (so 1.2 max differential). I can set it to as small as +-0.3 C (+-0.56F) or +-1F. The max setting is different for C and F degrees.

I have not found any specific sugesstions/guidelines to the differential that works best, i.e. what is the minimum differential that will keep the system running smoothly? My system is running well now, but once the yeast start to produce heat, the small differential may not be good. I'm guessing and I'm not really sure why this would be the case.

That's very similar to my setup and I've found it works really well. The only difference, I use a Brewers Edge heater which is essentially an adhesive-backed germination pad. It's stuck to the side of my ferm chamber. I use the smaller differential, 0.3C on mine. The probe is attached directly to the side of the fermenter then insulated from the ambient air temp by a block of rigid foam insulation. There's enough thermal mass with the full fermenter that it doesn't cycle between heating and cooling.

Okay, that's good to hear. I was afraid that too small of a differential would cause an issue. I can go to 0.3 C, but just didn't know if I should.

I monitored the temperature using a Elitech RC-5 USB Temp recorder. It's used for food distribution. I guess they throw these in the back of trucks with pallets of perishable goods. I think the temperature is off by a degree or so (records too cool I think). My thermostat, I am assuming is better but I still need to calibrate that as well.

Here is the recorder I use:

Here is the pad:

And I use the Ink Bird LTC-308 thermostat.

I want to show the difference between the temperature fluctuation when you a measuring the ambient air (and the heating pad not attached to the carboy) and when you have the temp probe insulated and attached to the carboy (with heating pad wrapped around carboy).

Here is with measuring ambient air:


Here is with measuring temp of carboy:

hlmbrwng said:

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Great thread. If the sensor is longer, is it be soaked into the carboy?

I put my probe in the wort and once it get to temp it seems to hold longer before my chest freezer kicks on. Plus I know I am getting wort temp and not the air temp, but I suspect after a while in a confined small space they should equal out fairly close.

inkbird said:

Great thread. If the sensor is longer, is it be soaked into the carboy?

Click to expand...

It would be ideal to have the sensor in the carboy, however, I wasn't really sure how to do that. I think that the sensor is long enough to do that. I'm not sure how you would put the sensor in the top of the carboy while there is a rubber stopper and a bubbler/blow-off tube.

Sailingeric, how do you do this? Do you have a photo?