What Thermometer should I trust? All skewed at certain degrees . . .

[djbradle]

I tested three thermometers I have:

1. Taylor digital function meat probe

2. Lab thermometer from Northern Brewer

3. Temp probe on 8 gallon brew pot from HomeBrewStuff.com ( only therm that can be calibrated)



At 150F degrees on the Lab thermometer I get 167F on the Taylor (active reading within the first 1.25 inches) and at boiling I get 209F on the Taylor and 210F on the Lab. I'm at about 600 feet above sea level on a rather humid day here in central MA with the A/C going inside the Kitchen. I had 4 gallons of water in the pot up to a boil with all three together at the same level in the water. Probe in the brew pot is about two inches submerged below the 4 gallons mark.

What to trust at 150F degrees? I set the Brew pot to the Lab therm just to be safe.

 

[prpromin]

I calibrate with boiling water and water with a healthy amount of ice in it. My lab thermometer reads 4 degrees low. I just made a note of it and do the quick math whenever I take a reading. I also check periodically to make sure it isn't more or less off - but after a year, it is still -4 degrees. It is my sole thermometer, so it's not a big deal. I suppose it would be a real pain if I had to calibrate (and remember) the difference on three different thermometers. My advice would be to pick one (or two, since one is on your kettle), calibrate, make a note, and stick with it.

Alternatively, you could buy one of those 60.00 pen instant read thermometers, but I can think of a lot better brew stuff to spend my cash on.

Good luck.

 

[crackhead7]

Get a thermo pen its the best thing I ever bought. I use it all the time for cooking as well.

 

[lschiavo]

Get a thermo pen its the best thing I ever bought. I use it all the time for cooking as well.

I agree. You may get lucky and get a cheap thermometer that is actually linear. I had collected quite a few before I got my thermapen and only one was even close. The worst was over 10 degrees off at mash temps.

 

[jldc]

+1 for a Thermapen.

Expensive but useful for lots more than beer.

L

 

[djbradle]

Thanks guys. Since I'm starting AG it's best I get something accurate since this is beer we're talking about, not water thermopen it is.

 

[zachattack]

I'll add that those lab thermometers from NB are awful, check out the reviews. Mine read 220 in boiling water.

 

[DSmith]

+1 for Thermopen.

I noticed this product after buying the Thermopen:
http://www.thermoworks.com/products/handheld/therma_k.html

It's the same price, slightly better accuracy and keeps the electronics away from liquid. A longer probe might also be nice for mashing.

 

[KISS Brew]

I recently ended up with a Thermoworks RT301WA, which after calibration reads within 0.5C at both freezing and boiling. For the price difference, I'll sacrifice half a degree here and there.

 

[mabrungard]

I'll add that those lab thermometers from NB are awful, check out the reviews. Mine read 220 in boiling water.

Brewers need a certified mercury thermometer that serves as their calibration standard for all their other working thermometers. As pointed out above, you can't rely on freezing point/boiling point readings to verify your working thermometers. You need to check calibration in the temperature range you're most interested in (~150F). Even expensive electronic thermometers have been known to malfunction and without an accurate calibration standard, you'll never know it.

 

[djbradle]

That's why I standardized my brew kettle probe to the mercury. I mean it's the age old standard anyways. I trust the 150 on the rising red stuff but would prefer the real mercury like back in science class. In the basement where I know it was about 70 the brew probe and lab thermometer were almost identical while the digital Taylor was reading 82! There must be something wrong with it.


***EDIT***

Not the mercury but alcohol NB thermometer.

 

[zachattack]

Brewers need a certified mercury thermometer that serves as their calibration standard for all their other working thermometers. As pointed out above, you can't rely on freezing point/boiling point readings to verify your working thermometers. You need to check calibration in the temperature range you're most interested in (~150F). Even expensive electronic thermometers have been known to malfunction and without an accurate calibration standard, you'll never know it.

The point I was trying to make is that the cheap alcohol lab thermometer from Northern Brewer is a piece of crap, and it's certainly not certified anything. I was in fact advocating the boiling/freezing calibration method, not discounting it. FWIW a brand new, factory-calibrated Thermapen does in fact read my boiling water at 212.

In the absence of a certified mercury thermometer, what do you recommend as the best way to calibrate a digital thermometer like the Thermapen? I was under the impression that the boiling/freezing check was the best way to do it, and that's what Thermapen recommends.

 

[DSmith]

There's little you can do except buy from a manufacturer that offers a test certificate from the factory and possibly send it back every so often.

I compared my Thermapen to a well documented industrial thermocouple and it proved accurate to less than a degree. I have cheaper units too and they were off a few degrees. The worst one was manfunctioning because water could get into the tip of the probe.

I work with special tolerance type K thermocouples for testing heat recovery equipment in refineries/power generation. The only thing you can do is send them to a lab where comparisons can be made to more precise instruments. If you document enough temperature points in ranges that you test then you can make corrections to the readings. The thermocouple readers have innaccuracies also so it's best to test the entire system.

 

[djbradle]

My Taylor must have water in it to read so far off. The NB therm is a better fit than that since its accurate to boil but I guess that at a lower temp it can be off. I can't see spending too much for one in my case since I brew for the savings mostly. I'll save some more cash for the thermopen if anything.

 

[mabrungard]

I am quite impressed with the Thermapen and its ability to provide very accurate reporting when operating correctly. I'm just leary of things that can't be verified by other, more verifiable means.

A Thermapen calibration is checked with an dense ice/water bath. They show what happens if you don't have enough ice in your water bath, with the temperature of the bath being several degrees high. So, with proper methods, you can at least verify that 32F set point. When that instrument is operating properly, they show that its linearity in temperature reporting with a known standard is very good. The problem is that there have been reports of even the Thermapen getting out of whack in the middle of those freezing/boiling check points. Without a good calibration standard to spot check that meter, you would never know its off. Even if you perform the ice/water bath check. I'm not sure there is another methodology to check the temperature reporting of a thermometer in the ~150F range that brewers are interested in.

 

[Wynne-R]

Does anybody know where to get a mercury thermometer? By golly if they’re going to be illegal, I want one.

 

[djbradle]

Well, most states consider mercury to be cancer causing and toxic and in certain applications mercury is not to be used especially for household use.

I ripped apart my old Delco boiler a few years ago and pulled out like three vaporstats with mercury filled glass controllers. I brought that to the local dpw and the guy gave me this look like "Whoa whoa be careful with that stuff!". I should have kept 'em and sold it to you!

In anycase I would say at this point from the info in the thread from more experienced brewers that even if my NB therm is accurate to boiling AND when I do a dense ice bath then it's possible that it's linearity could be compromised at the most important temp, the mash.

I'll do the ice bath with the NB one and see if it's pans out and if it does I'll try that for my first BIAB.

 

[djbradle]

I remember dropping one accidentally in science class and it shattered sending all the little mercury balls of different sizes into the sink drain and around the countertop. . I thought to myself , " hmmm that's a funny sight" haha

 

[BakRivrBruen]

I remember dropping one accidentally in science class and it shattered sending all the little mercury balls of different sizes into the sink drain and around the countertop. . I thought to myself , " hmmm that's a funny sight" haha

I remember my dad telling me when I was a kid that in his science classes they used to pass around mercury for students to play around with. He said they would swirl it around in the palm of their hands or let it drop on the desk so it turned into little balls. He still alive and he doesn't have hand cancer either haha.

 

[mabrungard]

Its not cancer that is the worry, its going crazy. Mercury affects brain function. You definitely want to avoid the stuff at all costs, but its not going to kill you. I remember playing with it as a kid too. My brain still seems to work.

 

[Denny]

Its not cancer that is the worry, its going crazy. Mercury affects brain function. You definitely want to avoid the stuff at all costs, but its not going to kill you. I remember playing with it as a kid too. My brain still seems to work.

Seems to.....

 

[alane1]

Iv'e read an alternative way of checking the accuracy of a thermometer is to run the thermometer in question under hot water between 90 and 100 deg.f until you get a consistent reading,then take another reading with a baby thermometer(which are supposed to be very accurate).

 

[Denny]

Iv'e read an alternative way of checking the accuracy of a thermometer is to run the thermometer in question under hot water between 90 and 100 deg.f until you get a consistent reading,then take another reading with a baby thermometer(which are supposed to be very accurate).

But how do you know if it's accurate at mash temps?

 

[LandoLincoln]

Someone needs to come up with a thermometer that is very accurate from 140°F to 180°F for us homebrewers.

 

[william_shakes_beer]

Its not cancer that is the worry, its going crazy. Mercury affects brain function. You definitely want to avoid the stuff at all costs, but its not going to kill you. I remember playing with it as a kid too. My brain still seems to work.

Remember the Mad Hatter in Alice in Wonderland? That character came from 19th century hatters that dipped felt hats into vats of mercury to make them waterproof. The mercury soaks through your skin with repeated exposure and causes sumptoms that resemble some forms of mental instability.

 

[djbradle]

More teeeeeaaa!

 

[djbradle]

Well I just checked two baby therms to my NB therm and they are exact. The two baby therm confirmed warm water in my brewpot at 102.3 and 102.4 respectively and what about the NB ? 102.2-5 ( can't get a 1/10 by eye) so I'm happy to use this for mashing. Baby therms are certified by ASTM.

 

[edroberts]

If you use a digital probe thermometer, just make sure it is fully waterproof. I had one that eventually corroded on the inside, leading to mash readings 15 degrees high, cooled wort readings 25 high, and dead accurate boiling readings. Yeah... That screwed up a couple batches.

 

[djbradle]

That was my problem with this one. I shoulda read the manual on it. 400 degree plus? No problem. A little bit o wort infusion? No good.

 

[daksin]

Professional scientist reporting in (By training and by trade): mercury thermometers are by no means illegal, though they are expensive to ship (thanks DOT!). Try Fisher or VWR if you NEED one.

As for brewing, calibrate a liquid-phase (alcohol) thermometer by immersing it in ice water which has been made by melting ice made from distilled water in a plastic or glass cup. Make sure it reads 0C (or record what it DOES read) and then BOIL that exact same water (should still be distilled water). Read that temp and make sure it reads 100C (or record what temp it DOES read). Liquid-phase thermometers should be REASONABLY linear (I've never had an issue with my mash temps, but I'm a long way from anal about these things). Digitals are much more finicky and difficult to calibrate at mash temperatures.

 

[Wynne-R]

I picked up a cheap lab thermometer from the LHBS for eight bucks. It was 1ºC low in a proper ice bath and on the money at boiling (corrected for altitude and barometric pressure.)

Digital thermometers are handy, but can be unstable for many reasons. It’s good to have a reliable reference.

 

[onthekeg]

I use these fella's to verify my Thermopen and thermocouples.
One is 0-50c mercury
One is 0-200c mercury

They are expensive thermometers that I took as trade in for the "safe" thermometers. I have had them about 10 years and they will last me pretty much forever, they stay in their case all the time.

 

[matt2778]

I don't understand why there always seems to be so much distrust for the alcohol lab thermometers. I recently broke the one that came in my original kit so I spent $35 on digital at the lhbs(that's all they carried). That pos went up during my first brew session with it. I decided to just order three more lab thermometers from ahb and calibrate them with ice water and boiling water. The worst of three was off by 2 degrees and the best of them was off by only one. At six bucks a piece I can do the math and furthermore if one breaks who cares. All that said a $100 dollars could buy me a whole lot grain, hops and yeast.

 

[benzy4010]

Thermapen

 

[Wynne-R]

I like to give wild guesses in precise figures because I think it’s funny. That’s sorta what the cheap digitals are doing, like 153.6 ± 3.
That’s about what ±1%, ±1 digit gives you.

The lab thermometer tells you 154 within a degree or so. They don’t care about ambient temperature, battery voltage, drift or whether or not they’ve been wet.

 

[ilv4xn]

I was in the middle of mashing thought I would double check the temp when all of the sudden my temp started climbing I didnt know what to do I calmed down when my mash reached about 215 and I didnt see a rolling boil in my cooler LOL

 

[lschiavo]

I was in the middle of mashing thought I would double check the temp when all of the sudden my temp started climbing I didnt know what to do I calmed down when my mash reached about 215 and I didnt see a rolling boil in my cooler LOL

Are you going to re-calibrate that one or throw it out?

 

[mike20793]

Thermapen. Solved all my problems.

 

[djbradle]

Now here's a ? Does the mash ever rise by itself a few degrees if already pulled from the burners?

 

[jldc]

Now here's a ? Does the mash ever rise by itself a few degrees if already pulled from the burners?

No. The mash is not an exothermic process. Rising temps means the mash wasn't fully mixed when the first temp was taken. Stir like crazy, then check temp.

L

Edit: I guess if the mash tun is hotter than the mash it could happen. In that case it's not insufficient mixing, it's not waiting for temp equalization. Same idea though.