Calibrate your thermometers!

[Huskysibe]

I learned the hard way to ensure your thermometers are calibrated before brewing. I brewed my first AG this past Monday and my temps were low because one of my thermometers was reading high. Here is an easy way to calibrate your thermometers, I did both but finalized with the boiling water method:

Ice Water Method
1- Fill a glass with as much crushed ice as you can and fill the remainder of the space with distilled or filtered water. If you do not have distilled or filtered water, use clean tap water.

2- Stir the ice chips and water.

3- Insert the thermometer's probe or stem into the middle of the glass so that it is not touching the bottom or sides of the glass. Submerge at least 2 inches of the probe into the ice bath.

4- Hold the stem in the ice bath for 30 to 60 seconds.

5- Adjust the hex adjusting nut under the head or dial of the thermometer so that the temperature reads 32 degrees F, which is the freezing point of water. If you have a digital thermometer, press the reset button to adjust the temperature.

Boiling Water Method
1- Pour tap water into a cooking pot and place it on the heat of a stove top element; bring the water to a rolling boil.

2- Place the stem or probe into the boiling water so that at least 2 inches of the stem is immersed; the stem should not be touching the sides or the bottom of the pot.

3- Hold the stem in the water for 30 to 60 seconds.

4- Adjust the hex adjusting nut under the head or dial of the thermometer so that the temperature reads 212 degrees F, which is the boiling point of water. If you have a digital thermometer, press the reset button to adjust the temperature.

 

[the_bird]

Technically, you'd want to adjust the boiling temperature based on boiling temps at your elevation. We're a little closer to 210° here (and a quick Google search indicates that you're at about the same elevation as us). Not too far off 212°, but this effect can be more noticeable for a lot of folks.

 

[Dahoov]

Technically, you'd want to adjust the boiling temperature based on boiling temps at your elevation. We're a little closer to 210° here (and a quick Google search indicates that you're at about the same elevation as us). Not too far off 212°, but this effect can be more noticeable for a lot of folks.

^^What he said^^

At my house water boils at ~ 203.

 

[Huskysibe]

Technically, you'd want to adjust the boiling temperature based on boiling temps at your elevation. We're a little closer to 210° here (and a quick Google search indicates that you're at about the same elevation as us). Not too far off 212°, but this effect can be more noticeable for a lot of folks.

Thanks, I didnt even think about that.

 

[h22lude]

Wow I was just going to ask what the best way to calibrate a thermometer was. Awesome post. Going to go try right now, thanks.

 

[SilverZero]

Technically, you'd want to adjust the boiling temperature based on boiling temps at your elevation. We're a little closer to 210° here (and a quick Google search indicates that you're at about the same elevation as us). Not too far off 212°, but this effect can be more noticeable for a lot of folks.

And really, you should correct for atmospheric pressure at the time of calibration as well. . . .

Come to think of it, maybe the freezing water method is best. Even so, it's important that it be distilled or at least as clean as possible, as solutes in the water lower the freezing point. Science!

 

[kh54s10]

If your dial thermometer is off at freezing and you adjust it then you check boiling and you adjust it your freezing temp is now off. Right?

Also it could be OK at freezing and boiling and still off at mashing temps. I think i read that anyway. Mine checks out pretty good all across the range. At least it agrees with my glass thermometer.

 

[LandoLincoln]

And the minerals in tap water can affect the boil calibration, so one should use distilled water for that as well. Or so I've read.

 

[normzone]

I was looking at this issue just last week.

I have several thermometers.

A digital temperature / humidity indicating box, battery powered.

A glass brewing thermometer.

A dial cooking thermometer.

A dial photography thermometer.

No two of them agree. Oh, they're all within a four degree range, but...

The photo model with the hex nut on the rear that you mentioned agrees with the digital temperature / humidity indicating box that I have at work, which bears a current calibration sticker.

Which means little, since just because it's apparently accurate at room temperature is not a sure indication that it's accurate at boiling or freezing.

I'll have to do the ice water / boiling water experiment and see what comes of it.

 

[Huskysibe]

I finalized on the boiling because I will be using it for the hotter temps rather than the colder ones. Figured it would be better that way.

 

[SilverZero]

I finalized on the boiling because I will be using it for the hotter temps rather than the colder ones. Figured it would be better that way.

As long as you know the boiling point of your water at your altitude.

 

[ElevenBrewCo]

can you even adjust analog thermeters? I bought a set from bobby m but never really thought about calibrating them....

 

[randomgnarkill]

Ok I have a question? I brewed yesterday and I am @ 6000 ft elevation. My temp gauge was reading 210 @ boil which is off. I should be @ 200.6. So I just subtracted 10 degrees from my temps. Did I mess up?

 

[Qhrumphf]

If your dial thermometer is off at freezing and you adjust it then you check boiling and you adjust it your freezing temp is now off. Right?

Also it could be OK at freezing and boiling and still off at mashing temps. I think i read that anyway. Mine checks out pretty good all across the range. At least it agrees with my glass thermometer.

This. Direct experience. Unless you're using a thermometer with a very narrow tolerance (and most inexpensive thermometers have a very WIDE tolerance), calibration at boiling and calibration at freezing does not an accurate mash temp make. It makes for an inaccurate thermometer, just calibrated in its inaccuracy.

I have a number of different thermometers. I checked em all against each other. Where one is accurate at boiling AND freezing, it's 5 degrees high in the mash range. Another is a little off at freezing, and 10 degrees high in mash range. One is about 5 degrees high across the board (analog and non-adjustable). And the agreement waxes and wanes, because they have a tolerance of +/- a few degrees in any given direction. When it comes to a few degree variance in strike water to reach a few degree variance in mash temp, I was all over the place and had rampant issues with overattenuation, despite having a thermometer I thought was properly calibrated (the one accurate at boiling and freezing). I finally shelled out the bucks and bought a Thermapen because its tolerance is very narrow compared to anything else we could practically use. And once I did so, I realized just how inaccurate these other thermometers were.

So point is, just because you calibrate it doesn't make it accurate. It's like taking a bunch of rounded figures, and then assuming the result you get after some number crunching with them is accurate to the 10th decimal place. You're dealing with an approximation to begin with, so calibration doesn't mean a whole lot, because the result is still an approximation.

Edit: Just a side note, the Blichmann Brewmometer on my kettle is the only thermometer that rivals my Thermapen in terms of accuracy (not perfect, but very very close). Although given its location on the kettle, it's normally too high to be of use for strike water and I mash in my cooler. I don't know its stated tolerance figures, but if you're using a Brewmometer for strike water/mash temp, you might be ok.