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I'm asking this because I recently made the switch to all grain brewing, and I'd like to make sure I'm as accurate as possible for mash temps.

I have a plain dial thermometer that I used for some extract brews (bought for ~$10 at my LHBS), but I'm not sure that I trust it. When I bought it, I calibrated it to 32F an ice water bath (lots of ice, just enough water to cover). Just for fun, I tried it in boiling water and it said that the water was only at 206 F after being immersed for 30 seconds in the boil (I am <1000 ft above sea level, so it should still be at 212 F), but still says I'm at 32 in an ice water bath.

Should I try to find a nicer thermometer or just re-calibrate the one I have to the boiling water? If I should upgrade, do you have any recommendations?

Edit: I should also add that I don't really have the funds to spend on a Thermapen.

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3 Answers 3

up vote 4 down vote accepted

I've found that all the dial thermometers I've tried have always been off a little, and aren't able to be calibrated properly. Either they are too low on the high end or too high on the low end and I can't get them to be correct for both boiling and freezing water.

Alcohol thermometers (the ones that look like mercury thermometers) always are dead on and don't need to be calibrated, and only cost $10 or so. They also have a lot more precision so you can actually tell the difference between say 148 and 150 (which might be important for a mash). I would recommend one of them, since they are pretty cheap and work well. However you have to store them properly (the alcohol will separate if you store them upside down and then they are useless) and you can't get them too hot or they will explode. But other than that they are cheap and work great!

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We just heat them until the alcohol forms a continuous line from bulb to top, to remove "bubbles". But you want to heat them slowly, as pj warns. –  drj Oct 28 '11 at 6:07
    
REALLY slowly. I tried doing this once on a thermometer that had separated and exploded the thermometer. moral of the story, store your thermometer vertical and upright. –  pjreddie Oct 28 '11 at 13:32
    
The best way is to get some dry ice and cool it until all of the alcohol is in the bulb. We only heated them when we didn't have some dry ice or liquid nitrogen around. The trick is to stop cooling just as the alcohol goes into the bulb. –  drj Oct 29 '11 at 6:20

Calibrating a thermometer to boiling and freezing temps is not a good idea unless you mash at boiling or freezing temps! As you've seen, it can be on the money at one extreme and way off at the other. I used a calibrated, NIST certified lab thermometer to calibrate my bimetal dial thermometer that I use for brewing.

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+1 to calibrating in the range you actually use –  dana Dec 21 '11 at 18:56

I've had great luck with using a digital probe thermometer (ie like the ones used for cooking and reading meat temperatures) for mashing, cooling, boiling, etc. etc. etc.

I have been through 2 floating thermometers, one lab thermometer, and a Blichmann weldless brewmometer, which, even though I shielded it from burner heat, lost its hermetic seal and essentially says I am at 195-230 degrees when boiling. troll some of the forums for recommendations on the best thermometer (there's one that will be the last thermometer you ever buy)....using accurate equipment will definitely improve the quality of your beer.

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