Remember that time you said to your dinner guests, “the thermometer said it was at a perfect 135!” right before serving them a sadly overcooked piece of meat? Well friend, I’m here to tell you, that thermometer that you bought goodness only knows how many years ago, that you dug out of the kitchen junk drawer five minutes before you used it, is probably not calibrated correctly anymore. Scratch that. It’s definitely not calibrated correctly anymore.
When I say calibrating a thermometer, here’s what I mean: testing it to be sure that it’s reading temperatures within an acceptable degree of accuracy and, if it’s not, adjusting it so that it does take temperatures accurately.
Now, I’m not recommending any kind of thermometer in particular here in this piece but, if you read the piece I wrote about essential kitchen tools, you know I generally prefer a thermocouple digital thermometer -called the thermapen- at my house. The important thing to know for now is that thermometers can fall into two main categories
- Digital: A digital face and a metal probe. Sometimes folding to protect the probe. Thermocouple- like the thermapen- and thermistor thermometers fall into this category, though they work slightly differently. Some can be calibrated, and some can't.
- Dial: A clock-like dial face replaces the digital face, and a metal probe, generally thicker than a digital probe. Bimetallic coil thermometers fall into this category. Almost all can be calibrated.
Of course, there are a few other kinds of thermometers- like the kind with a cord and a probe that stay in the oven, while the actual reading device stays outside. But, since these can't be calibrated, I don't talk about them here. Again, I’m not weighing the benefits and drawbacks of digital vs. dial thermometers here, except to say that dial thermometers don’t hold their calibration all that long, but are quite easy to calibrate. In comparison, digital thermometers tend to hold their calibration relatively well, but can be a little more involved to calibrate.
So, now that we know you need to test and calibrate your meat thermometer, let’s talk about how to do that. The basic idea is that you create an environment where you know, for a fact, what the temperature is. Then, you use the thermometer to measure that environment and see if it reads the right temp. Since we know that water freezes at 32 F and below, and we know that water boils at 212 F, either one of those makes a great “environment” for us to test with our thermometers.
One note: for most calibration procedures, I prefer to use an ice bath at 32 F as opposed to boiling water and testing for 212 F. This is because the boiling point of water changes at different elevations, and I don’t want to have to account for that temperature change. For some digital thermometers, however, (like the thermapen) you need to use both environments.
To test any food thermometer:
Create an ice water bath. This is the important part: it must be majority ice. So, grab a measuring cup and put in enough ice to come up to the two cup mark. Giant ice cubes don’t work as well here. Then, pour water over the top, stopping when the water just comes about an inch above the ice. Stir it all around.
Put the probe of the dial thermometer into the water, with 3 inches of the probe immersed in the ice bath. Wait to let the probe equilibrate at least one minute (unless you have a fast reading thermocouple thermometer, in which case you don't need to wait as long).
- Read the temperature. The thermometer should read the temperature of the ice bath as 32 F, within 2 degrees of accuracy.
To calibrate a dial thermometer: If the thermometer is not reading correctly, you can use a small wrench to twist the nut underneath the thermometer face. Be gentle! Slight adjustment should be all that’s needed. For quickest results, you can adjust the nut with the probe still in the ice water.
To calibrate a thermapen thermometer, see this guide: https://www.thermoworks.com/pdf/user_manuals/Thermapens/Thermapen_Original_Calibration_Manual.pdf
For other kinds of digital thermometers, be sure to check online manuals or your own manual to see the exact procedure.
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