thermowell issues

I have a concern about the use of a thermowell- On one brew I used a thermowell and I think that it caused a large fluctuation in temperature of the wort. For example-my deep freezer would get below freezing and would hold a lower temperature than the desired fermentation temperature of the lager wort because the middle of the carboy was still warmer-anyone have any input?

 

Was the thermowell in the beer? If so then the controller should have been maintaining the temp of the beer where you wanted it...

 

During the active part of fermentation, temperatures in the beer can be wildly different between the temp at the outside edge of the fermenter and the middle where your thermowell is. By as much as 10* i have heard.

As long as you aren't shocking the yeasties by frosting the outside of your fermenter I think you'll be ok with the setup you are using

 

I don't believe that's correct. The beer is pretty turbulent during active fermentation, and in any case liquids transfer heat very efficiently, so I'm pretty sure that the temperature of the beer is going to be uniform. JZ has stated on numerous occasions that taping a temp probe to the outside of the fermenter (and insulating the air-side of it) provides a very close reading to what you'd have in a thermowell.

There can be a large difference between the temperature in the carboy and the ambient temperature but that is a different matter.

 

I guess the real question is that a freezer might ambiently cool to 30 while the thermowell. Registers let's say 45 degrees. Then that ambient temp will persist lowing the temp more. In a chest freezer.

 

you're correct, the air temp will fluctuate a little bit.

in my experience this has been minimal.

 

If the temperature of the beer is within a degree or two of the required temperature, then I have found that the thermowell works very well.
However, if the beer is several degrees warmer than the required temperature, then you can overshoot on the cooling as the beer will not cool as quickly as the ambient temperature within the freezer as you said.
The only times I have had this problem are when adding a new primary to the freezer. The wort may not be sufficiently cooled, especially in the summer, or when brewing a lager. What I do in this case is to insert the probe fully in the thermowell and read the temperature after 5 - 10 minutes. If the temperature reading is within two degrees of the required temperature, I leave it. If the wort is > 2 degrees warmer than required, I raise the probe so that it is above the level of the wort. In this case, the probe is influenced both by the temperature of the wort and the ambient temperature. I then measure the actual wort temperature every couple of hours until it gets to within 2 degrees of the required temperature, when I put the probe where it belongs.

-a.

 

I am noticing that a fridge cannot keep up cooling as fast as the wort temp rises at h krausen. It seems like even controlling the wort temp there is an initial temp spike.