Endless thermometer calibration

[Patirck]

I've been having some problems with attenuation lately so I decided to take a look my thermometer calibration to make sure I wasn't mashing too high.

I have a blichman 3" dial thermometer in each of my pots. I have attempted to calibrate them using both the boil/ice bath method as well as matching it with a floating thermometer I got from the LHBS. Depending on which method and when I do it, I'm anywhere from 1 - 4 degrees high or low. It never seems to be consistent in either direction.

I started using the floating thermometer in the last two batches and while I know that different parts of the kettle will have some temperature differences, I consistently saw 3 degrees difference in the last two batches - the only problem, was that one batch read higher with the floating thermometer and the next was lower.

Is this an acceptable rate of error? Am I being unrealistic to want to see 149* on each thermometer?

Any suggestions?

 

[day_trippr]

Get one of these....

Cheers!

 

[Patirck]

What makes this one more accurate than any of the other (seemingly) 8 thermometers I have?

 

[GotPushrods]

The bottom line is that even good dial thermometers are not necessarily accurate across all temperature ranges we might encounter as brewers.

I advocate calibrating the HLT thermometer to 170, the MLT to 150, and the BK to 60. (Assuming you chill in, or recirculate back into, the kettle)

To do this, you will need a thermometer you trust at each temperature. A lab grade alcohol or Mercury thermometer might seem best, but you can get a very accurate digital for pretty cheap these days. I don't have an exact recommendation on model, but you get the idea. You'll have to decide on your own threshold for accuracy/price ratio.

Depending on the technology of the thermometer, yes, some will be more accurate than others. Digital thermometers do not directly measure temperature (much the same as a TDS meter does not measure TDS). They measure voltage or resistance, using those values to estimate temperature. There are a number of factors that will determine the accuracy in the end... i.e. cold junction compensation or the complexity of the polynomial used.

I would suggest any brewer do a little reading on thermocouple vs thermistor vs RTD to get you started understanding the technology we take for granted every brew day. It will make it immensely easier to make these types of decisions, and trust your results.

 

[bob352]

Your floating thermometer probably has good repeatability at mash temps.

Many folks report similar problems with mechanical thermometers.

If you are not doing some kind of automated recirculation (rims/herms)
then a +/- 3 F variation in mash temp is not surprising.

Yes, it is unrealistic to expect a bunch of thermometers to all read 149.
You might be able to get good accuracy by averaging the readings.

Yes, it is unrealistic to expect your mash temp to be a consistent 149
throughout the mash without some kind of automated recirculation.

A good digital thermo helps. I like my thermapen.
But there are under $30 digital thermos that give good results.

Bob

 

[day_trippr]

What makes this one more accurate than any of the other (seemingly) 8 thermometers I have?

8? Really? I might not have all of them covered

- But, fixed mechanical thermometers aren't very useful for measuring mash temperature, as they're fixed, and they're mechanical. With the typical short probe length, I would be disinclined to trust them even with a recirculating mash.

- And floating thermometers can tell you what the surface temperature of the mash is, accurately and with good repeatability. But the surface temperature could be many degrees below the temperature in the middle of the tun.

Otoh, the device I linked is relatively inexpensive (especially right now), very accurate, fairly fast, and can reach the bottom of the typical home brewer's mash tun. And it's sold by ThermoWorks, who have a decent track record. I have one on my 10g cooler tun, use it to check how thoroughly the mash was stirred, then stick it through a 1/4" hole in the middle of the lid and leave it there 'til the mash is finished. I've compared it to my Thermapen at various temperatures and it tracks within a couple of tenths °F...

Cheers!