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Old 04-05-2011, 04:34 AM   #1
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Default Thermometer calibration - how do YOU do it?

I've been getting some poor attenuation for several batches now, and I came to the conclusion that my thermometer was at least 2 to 4 degrees low. So I was mashing at 158 instead of 154, for example. With no time to get to a store on a busy brewday, I just compensated on-the-fly.

So how best to calibrate?

1. Boiling water, it should read 212 (or compensated for altitude).
2. Buy a laboratory instrument, with a certificate of calibration and traceable to the National Bureau of Standards;
3. What is this "calibration" thing of which you speak?

Anyway, I guess I'm just venting. But I do want to trust my thermometer.

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Old 04-05-2011, 04:41 AM   #2
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glass of ice water should read 32, I would trust it more than boiling

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Old 04-05-2011, 04:42 AM   #3
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Ice/water mix at 50/50 mix. Swirl your thermo for a few minutes and you should get within .5 deg or right at 32

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Old 04-05-2011, 05:13 AM   #4
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I like to do a two point calibration for my mash thermometer, boiling and ice water, since mash temp is much closer to boiling than ice.
I buy ~15$ thermometers from restaurant supply stores that have hex on the back that lets you calibrate them. I recommend either using two to prevent errors or calibrating in the boil each time.

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Old 04-05-2011, 05:19 AM   #5
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The down and dirty way is what has been stated. A water/ice mixture should give you 32 degrees, and boiling (assuming you are not at high elevation) should give you about 212 degrees.

If you want to get more precise then I'm afraid you are as you stated in the initial post needing a laboratory grade instrument. Comparing your thermometer to a higher accuracy thermometer with a known good calibration is where you want to be.

You could also send it to a calibration laboratory, but unless it is a high reliability instrument, you have no guarantee that it will hold it's accuracy anyway. In the end it is best to spend a bit more on a thermometer with a proven track record, and compare it against other good thermometers when the opportunity arises.

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Old 04-05-2011, 10:49 AM   #6
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When calibrating, make sure that your measurements are taken in DI, not wort. Dissolved substances raise the boiling point and lower the freezing point, which could throw off your calibration.

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Old 04-05-2011, 12:52 PM   #7
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I have tried calibrating my thermometer in boiling water but I don't really know what is considered boiling. Is it when you see the first bubbles rise to the surface or when you have a rolling boil? I get 206 when I first see those tiny bubbles and hit 212 when it is a rolling boil.

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Old 04-05-2011, 12:56 PM   #8
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Quote:
Originally Posted by BWN View Post
I have tried calibrating my thermometer in boiling water but I don't really know what is considered boiling. Is it when you see the first bubbles rise to the surface or when you have a rolling boil? I get 206 when I first see those tiny bubbles and hit 212 when it is a rolling boil.
those first bubbles are gases being released from the liquid. the rolling boil is where you want to be calibrating.
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Old 04-05-2011, 01:05 PM   #9
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It's boiling when the flame is screaming and the water won't get any hotter.

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Old 04-05-2011, 02:07 PM   #10
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In reality, the boiling/freezing comparison is not accurate when you're calibrating a dial thermometer. It should be calibrated at the range in which you expect to use it. Unfortunately this means you need a good digital thermometer like a thermapen.

I recalibrate my thermometers every time I brew, and I usually find that they do need a small adjustment (1 degree or so).

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