Temperature Difference between Thermowell and External Probe?

[raouliii]

I am using a small commercial cooler as a fermentation chamber. It is equipped with a temperature controller with the probe firmly pressed against the glass carboy under a 3/4" layer of closed-cell pipe wrap foam. I have calibrated the probe.

I have never attempted to compare this temperature monitoring method against an actual temperature reading of the liquid within the carboy due to the lack of a thermowell. I have always assumed that the offset would be negligible, in the range of a tenth of a degree or so.

Has anyone made a comparison between actual liquid temperature and external probe temperature readings? Am I way off-base in my assumption?

 

[Sea]

The temperatures will vary quite a bit during initial cooling, changes in temperature within the cooler, and fermentation, as the yeast create some heat while they work. Once fermentation is done, and the cooler is kept at a steady state, the temperatures will be identical.

 

[Stauffbier]

I have a fancy/expensive probe-type thermometer (made by Fluke) which is used in the HVAC/Refrigeration industry. I keep one of the probes taped to the side of my FV and covered with insulation just like you, and the inside temp always matches +-1F.. For what it's worth (for those who like to bash fermometer strips) it also matches the fermometer strip on the side of the bucket/carboy.....

 

[blackstrat5]

I've noticed my strips on the side of the fermenter usually reads a combination 6 degrees. As the fridge comes on to bring down the temp the outside of the carboy cools faster than the interior so I'm getting a range on the strip.

I'm not a 100% sure how the interior temperature of the fermenting beer compares to what my probe is reading that's taped to the side with some insulation over it.

 

[Stauffbier]

As Sea said, at first the difference will be varried, but once it's been in there long enough the temp will equalize more. On my fermometer, when the temp reads a combination of 4-6 degrees I take the number in the middle. It always seems to match what my probe says. You could always pull a hydro sample and check it's temp real fast before it has time to warm up and then compare it to your probe temp...

 

[solbes]

I tape my external probe to the side of the primary. I use a folded up paper towel & tape to insulate the probe from changing air temps. Conduction from the primary should dominate any variability from convective air temps.