Two different temperature readings...which to trust?

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Gritsak

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I just made a batch of beer yesterday and have the primary sitting in a large bucket of water to keep the temp constant. The stick-on thermometer on the side of the primary reads 64-65*(it is submerged in the water). I've also got my long dial thermometer sticking in the water, and it's reading 70-72*.

I'm leaning towards the dial thermometer being correct since it would be very odd if the water temp was warmer than the primary (especially since it's actively fermenting).

Are the stick-on liquid crystal thermometer not very accurate?
 
Check the accuracy of the dial thermometer with crushed ice and water (32*F), then boiling water (212*F). If it's off, then you can determine how much compensation you need to make with measurements.

I'm not sure about the accuracy of liquid crystal thermometers, but I've always treated them as ballpark figures-- not as accurate as other thermometers.

-Steve
 
I agree with savage on calibrating the dial thermo.

Is the stick on thermo submerged? Those are not supposed to be under water, and can be inaccurate / possibly ruined if kept submerged.

IF that thermo is under water, I'd suggest using less waer, or raising the location on the carboy.
 
The stick on thermometer is submerged..I didn't realize that would mess them up. Oh well, at least they're cheap.

I'll check the calibration on the dial. It's new and looks to be pretty good quality, so i'm hoping it's not too far off.
 
Well it turns out the almost brand new dial thermometer is way off. It was reading over 40* in a half frozen section of an ice tray. So, the last 36hrs of fermentation has been in sub 65* temp range. oh well.
 
You should double check that reading in a proper mixture of crushed ice and water-- I'm not sure that a half frozen section of an ice tray is 32*F.

Did you check the boiling point?

-Steve
 
My stick on thermos seem to be very close to what a good alcohol thermometer dipped into the fermenter shows. However, whenever I have had one get wet (even from the wet T-shirt cooling method) it pretty much ruined it. There was a thread a few weeks back that suggested putting shipping tape over the stick on thermo as a way to keep it dry. I have done that with my new ones and so far so good (they aren't submerged though)
 
You should double check that reading in a proper mixture of crushed ice and water-- I'm not sure that a half frozen section of an ice tray is 32*F.

Did you check the boiling point?

-Steve


Just checked the boiling and it was right around 212...checked the ice again, this time punching through the top layer of a partially frozen cube and got a reading of 52*...something is screwy.

I also took some of the water out of where the primary is and put it in my flask that has a stick on thermometer on the side and was getting a reading about spot on to the submerged one that's on the primary (~65-68* now)
 

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