Trusting Thermometers

[monkeybox]

I'm doing all grain batch sparge, and it seems like everything is asking for very precise temperatures. And through the past year, I've used a couple different thermometers:

* I have a floating thermometer that came with my initial brew kit, where the difference between 150 and 160 is about 0.5cm.
* I have a digital remote meat thermometer that claims accuracy to 1 degree, and served me well for roasts in my oven, but once I used it for a mash, it decided it would not register any temperature under 138, even when I let it rest at room temperature.
* I have an 'instant read' "waterproof" thermometer that claims accuracy to 0.1degrees, which is clearly not waterproof at all since I dipped it in sanitizer and now there's liquid inside the LCD. It worked for the brewday, but now it won't display anything.

The thing is, during brew day, the variance between the three thermometers was > 10 degrees. I was aiming for a 156 degree mash, and all I know for certain is that I can't trust any of the thermometers.

What thermometers do you use, and why do you trust them? Any you can leave in the mash and/or the boil? How do you establish trust when you're 0/3?

 

[KBentley57]

You could always try to calibrate at least one of them, or perhaps all three. Just take a glass of ice water that has had time to stabilize in temperature and stick a thermo in. It should read a nice happy 32 F. If they can stand the temperature range, do it with a nice boiling pot of water; they should of course read 212. If you get these two points, you can make a calibration curve for each to predict temp they show at 156 degrees.

 

[Fordzilla]

Crushed ice in water test always works within for me. If it's within a couple degrees there I trust it at higher temps.

 

[AndrewD]

I have a dial thermo and a 20 dollar digital from the hardware store. I calibrate/test with the ice water method. For the ice bath, I want the highest ratio of ice to water to get accurate calibration. The water is just a conductor from the ice to the thermometer. Before I got the digital, I was setting my dial thermo to 33 degrees to account for any difference in the water temperature, but comparing to my digital shows me that I should have just been setting the dial at 32 the whole time.

 

[oakbarn]

I calibrate mine at 150 (using a calibration thermometer as a guide). You need to calibrate on a regular basis. I calibrate at 150 because the MASH temp is most important. I have found most digitals to be close but note any difference if they cannot be calibrated.