How can a thermometer read below freezing in water?

So how can a thermometer read below freezing when the water is liquid? I have had it read even lower than what is in the pic as well.
The liquid is just plain water out of the tap and is not frozen in the least. It is just in an old jar I use to test the temp of the fridge.

its broken

Time for a new one!

brewingmeister said:

So how can a thermometer read below freezing when the water is liquid? I have had it read even lower than what is in the pic as well.
The liquid is just plain water out of the tap and is not frozen in the least. It is just in an old jar I use to test the temp of the fridge.

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Theoretically the water could be supercooled somehow. But more likely, it's busted.

Even if it is the can do no wrong thermapen?

brewingmeister said:

Even if it is the can do no wrong thermopen?

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Well in that case, obviously operator error

Time to get new toys, darn!

Is there salt in the water??

I work in an industry that requires expensive test equipment which cost a pretty penny and is calibrated on a regular basis. A use and forget electronic precision measuring device of any sort is unrealistic. Thermapens are a great product. It's just not realistic to expect them to work perfectly forever.

PMEL I always hated dealing with them

No salt, it is straight tap water. This pic is water I put in there this afternoon. I have had the thermapen for a little over a year.

So the therapen isn't perfect. It happens. What you can do is make a temperature correction chart. Unfortunately you will only have two corrections. Ice cold water and boiling. The first is 32F the other is 212F (well 212 if you're somewhere around sea level, and even if not the boiling temp does'nt change a lot a few thousand feet above)

Just record the knowns to the readings.

Honestly though, 1 or 2 degrees off will not make a huge difference in mash temps or pitching temps.

You are using one of the better thermometers on the market. Unless you're ready to spend significant money on a thermometer that is calibrated on a regular basis. What you have is perfectly acceptable.

Temperature control is important, certainly. But perfect in home brewing term is with in 1-2 degrees. Anybody who claims their temps are spot on, measured by the products available are fooling themself.

Ok done rambling.. just my 2cents.

If one of those thermopens gets any moisture in it, it can get real wacky...I would just get a new one if it does this consistently.

What does it read in boiling water?

It appears all the fairydust has leaked out of the thermapen. The biggest problem is that it doesn't have a recalibration feature.

bja said:

What does it read in boiling water?

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Good question. My elevation is 650 ft if that helps.

brewingmeister said:

Good question. My elevation is 650 ft if that helps.

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At your elevation the boiling point is 210.85*F

Well, losing the fair dust is very disappointing. I have been through at least 8 or more thermometers in my years of brewing. Went through them all from analog dials, to cheap digital, to better digital, to digital probe, and to the thermapen. The thermapen was the only one that did not cease to function after a week or two and had actually read at least what I thought was an accurate temp. Just throwing it out and buying another hundred dollar or more thermometer isn't in the cards. I use the thermapen for everything brewing and food related so not being able to rely on it is quite disheartening. Anyone have any luck with having a thermapen calibrated or have a thermapen act like this?

I've come to the conclusion that the relative accuracy of the thermometer (within reason) isn't as important as the repeatability. Being off by a degree or 2 isn't going to make a noticeable difference.

I would hold Thermoworks to the fire on it. I'm sure they'll replace it or at least re-calibrate it. If that is not the case on a $90 thermometer, it was never worth it to begin with.

Sorta off topic, but is there ice in the glass? I'm wondering because I can't see it, and it would be required to have 32F temps. I've been thinking about buying of these type pens. However I think I'll go with the cheaper model. It has excellent reviews and is currently on $20. Of course there are a couple bad reviews but you get those with everything. Here is the cheaper Thermoworks version, the RT600C. At that price I wouldn't be as upset if it only lasted a year.http://www.amazon.com/dp/B002GE2XF8/?tag=skimlinks_replacement-20

l3asturd said:

Sorta off topic, but is there ice in the glass? I'm wondering because I can't see it, and it would be required to have 32F temps.

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OP states no ice.

It reads low at both ends, less so near boiling. I would just add 1 to whatever it reads (for mash and HLT temperatures) and carry on.

passedpawn said:

OP states no ice.

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Ahh I reread and see that he states he uses it to check refrigeration temps. So I guess my real question would be what temperature is the OP expecting the water to be? I ask to get an idea of how far off the probe is.

Exbeerienced said:

It reads low at both ends, less so near boiling. I would just add 1 to whatever it reads (for mash and HLT temperatures) and carry on.

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I don't think it's only 1 degree off in the low end. The water without ice is not 32F so it must be at least a few degrees off, possibly more in the low. But you may be right at about 160 it may only be one or two off.

Why's everyone talking about a new thermometer/sending it in/etc?

Can't you re-calibrate thermapens? Or is that just the newer ones? I'm pretty sure you can on mine. I was expecting to have to do this every so often...

Found it:

http://www.thermoworks.com/pdf/Thermapen_Original_Calibration_Manual.pdf

zachattack said:

Found it:

http://www.thermoworks.com/pdf/Thermapen_Original_Calibration_Manual.pdf

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Great find! Glad this can be done.

Yeah, I was completely uninformed by stating that you can't recalibrate a thermapen. Sorry about that.

I noticed the inaccurate reading when taking the temp of a jar of water that is kept in my ferment /cold crashing fridge. Right around freezing is what I aim for when cold crashing. There was no ice in the jar or in the airlock which is also plain water. If it said the water in the jar was 29 I don't know how low it would of actually gone with something frozen or slushy.
That thermapen calibration procedure is good to know, however the model shown is the older model. I have a message in to thermoworks so we'll see what they say.

brewingmeister said:

I noticed the inaccurate reading when taking the temp of a jar of water that is kept in my ferment /cold crashing fridge. Right around freezing is what I aim for when cold crashing. There was no ice in the jar or in the airlock which is also plain water. If it said the water in the jar was 29 I don't know how low it would of actually gone with something frozen or slushy.
That thermapen calibration procedure is good to know, however the model shown is the older model. I have a message in to thermoworks so we'll see what they say.

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You should be fine, keep us updated! I bought a thermapen a few months ago and I'm pretty sure they had a calibration procedure in the manual that came with it. I wouldn't have paid that much money for an instrument I couldn't calibrate.

You need to stir some ice in that water so you know exactly what temperature it is supposed to read.

brewingmeister said:

Even if it is the can do no wrong thermapen?

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i lol'd at that... got my head bitten off a few times for questioning thermapens in the past

Got a response back from thermoworks. Message states 'they rarely see accuracy issues with the splash proof thermapen'. So it does happen but not too often and I happen to be the lucky sob to have issues.

They go over the proper way to do an ice bath test and eventually say they will evaluate it for free if I send it in to them.

The issue that is getting muddled by thermoworks and some who have responded here is that the reading I was getting in the water of 29 was just that...a reading of water. I was not doing an ice bath test and there wasn't any ice in the jar. It was the temp of a fridge, a keg and a jar of water.

I will try testing temp reading later by going from boiling to freezing a couple times and see what comes of it.

So it took a while to actually do the testing on the thermapen. I did two rounds of testing one before I recently brewed and one after. In between it took temps of a kegerator, strike water, sparg water, and some food. Both times I started by putting water on the stove and while it gets up to a boil preparing a proper ice bath. I started by going back and forth from hot to cold after getting a stable reading.
Test #1 showed the first few readings were off. Started with the boil, it was off low. Freezing was off low as well. After a few back and forth between hot and cold readings things seemed to even out and boil reading was about where it should be for my elevation. Freezing started to come in dead on. Maybe 5-8 cycles of hot/cold readings to get accurate measurements.
For test #2 the setup was the same, going from boil to freezing tests again. This time boil started low and freezing was high. Freezing was really high actually,didn't get near freezing for the first couple hot cold cycles. Took a few rounds but freezing finally would go to freezing. Boiling for my altitude was achieved quicker. Took around the same cycles to get accurate readings the second time, around 5-8.
Going from boil to freezing seems to have adjusted the thermapen. I did not take apart or attempt to calibrate the thermapen other than make it go from boiling to freezing. Not sure if this would qualify as a calibration technique but it seems to have helped...if only for a week. Test your thermapens weekly apparently.

brewingmeister said:

Not sure if this would qualify as a calibration technique but it seems to have helped...if only for a week.

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You didn't calibrate anything. Sounds like that thing has some serious repeatability issues.

bja said:

You didn't calibrate anything. Sounds like that thing has some serious repeatability issues.

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I totally agree. It seems the going back and forth between known set points must have smacked some sense or fairy dust back into it.