Thermometer 10 degrees off!

[peroua15]

Hi all, I need to vent on here about my recent faulty thermometer discovery. Have made 6 batches off all grain and partial mash. I just decided out of curiosity that I would test this thing in boiling water. It was ten degrees lower that what the boiling point temperature should be for water! I have been wondering why my beers have been finishing with higher gravity than i expected/wanted. I have read about checking thermometer, but haven't really taken it seriously since I got it from my college chemistry lab. Well this is really a downer, all this time my batches have been getting screwed up because of a f***in inaccurate thermometer.

Lessen of the day: I was too lazy to take 5 minutes to check my therm. accuracy. So don't be like me. RANT OVER

any others have experience with faulty thermometers??

 

[cheesehed007]

Any way you can recalibrate it? Also test it in a glass of ice topped off with water.

 

[stevedasleeve]

Well it's and easy fix of course but still irritating. Hydrometers - every one I've had - are all inaccurate, I switched to an expensive refractometer about 20 brew days ago and will never go back. It took several thermometers before I found one that was actually accurate. Live and learn, but also it is best to brew a whole lot and base your process on collected information. After 100+ I'm pretty sure of what I'll get now, which is gratifying and also means I am reluctant to change anything on my rig or process, and frankly why would I since my beer is fantastic!

Cheers,
Steve da sleeve

 

[peroua15]

Any way you can recalibrate it? Also test it in a glass of ice topped off with water.

is there a way to recalibrate a mercury thermometer?

 

[Jayhem]

is there a way to recalibrate a mercury thermometer?

You can do what I do. I know mine reads 2F high so I know that if I want to mash at 152F the thermometer needs to read 154F. Pretty straight forward, no?

 

[ianw58]

First, you shouldn't even think of using a mercury thermometer in brewing. One mishap, a broken thermometer and you and the brew are exposed to mercury.

Second, the boiling point of water will change with atmospheric pressure. That means that the further above sea level you are, the lower the boiling point will be. Also, as the ambient pressure changes, so will the boiling point of water.

The ramifications of this is that using boiling water to calibrate your thermometer is not a valid exercise.

Having said that, I recently checked the dial thermometer in my mash tun. I calibrated it to 0°F in an ice bath and then checked it in boiling water. I live a couple of hundred feet above sea level and near enough to an airport to get barometric readings. The water was boiling at an expected temperature of 209.8°F. That was verified with a decent digital thermometer. The dial thermometer was reading 202°F.

At 155°F measured by the digital thermometer, the dial was reading 148°F.

Here's a great site for more info...

http://www.thermoworks.com/blog/2010/10/making-a-proper-ice-bath/

 

[TrickyDick]

Agree on the mercury thermometer. Most "lab" thermometers use a Ed alcohol solution and not mercury anymore. Do not use mercury, a liquid and toxic metal at normal environmental temperatures.

I do not believe it possible to calibrate such a thermometer, but its accuracy can be checked and then you could correct the temperature reading if it is significantly off.

Thermo works makes a thermapen thermometer. I highly recommend but it's relatively pricey, and isn't water proof. Splash resistant however.

I had an old long stem bi-metallic thermometer that was waaayy off and had similar problems. I have never met a thermometer I trusted until I got the thermapen. I have not tried using my IR thermometer to test liquids. I suspect it wouldn't be very accurate for brewing.

The cheaper digital thermometers sold at online brew supply stores seem to be accurate and less expensive than the thermapen. I think there is a CDN or some such model I also own and it is very accurate compared to the thermapen.

TD