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Temp. difference between on-glass & thermowell?

I have several different ways I can/do measure temperature of my fermenting beer:

  • stick-on liquid crystal thermometer on exterior of glass carboy; and [/*]
  • digital temperature probe in thermowell; or[/*]
  • digital temperature probe on exterior of glass carboy.[/*]

My digital temperature probe is linked to the temperature controller for my fermentation fridge. I usually use the thermowell, except when I’m expecting blowoff, in which case I tape it to the outside of the carboy.

My question is this: has anyone explored the temperature differences between these two or three methods? Ultimately, when I use a blow-off tube, should I be setting the digital controller a few degrees lower?

I always insulate against the fermentor. While doing this, I have also taken the temp by just sticking my thermometer in. It has always been within a degree for sure.

I always use a blow off tube and just wrap the probe with an ace bandage against the carboy for insulation (and it doesn’t leave tape residue!). I have measured the temps and they are very close, not even a full degree the last time.

That makes me feel much better about my lack of a thermowell. Thanks!

I have a standard floating lab thermometer on a fishing line that is threaded to the airlock bung. When I pull out the air lock, the thermometer is sure to follow.

Relevant question. My Johnson analog probe dangles :smiley: in free air (ambient) but I reduce 4 degrees for heat generated by the ferment. I’ve often wondered if things would be improved by touching the glass. Noticeable? Any thoughts? A little freaked about kinking the line.

The analog probe for which the line is plain copper wire? I have one for my kegerator, and it’s looped like crazy; still works just fine.

I’d guess that surface contact is going to be a big difference in temperature. Glass isn’t the best heat/cold conductor, but compared to an airgap, I’d imagine the discrepancy could be large.

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