As I had previously talked about in my Kitchen Tools 102 post, food thermometers can play a crucial role in cooking. Food thermometers help measure the internal temperatures of food and determine how far the food has been cooked, and whether it’s safe to eat or not. Using a food thermometer is an important part of practicing food safety at home! That’s why it’s important to know how to calibrate a thermometer, instead of buying a new one each time yours starts to give weird readings.
There are various different types of thermometers available to the home chef, which also include sugar thermometers, but for now I will concentrate on the two most common thermometers that would be used by at home cooks. Most people I have met, assume once a food thermometer starts giving wonky readings that it is broken, and time to go buy a new one! Before you do, keep reading! Most food thermometers are able to be re-calibrated from home.
Mechanical Food Thermometers (affiliate link) use a bimetallic strip which is a very thin coil of metal (imagine a spring) on which the dial or pointer that you see is attached to. As you take the temperature of an item with one of these thermometers, the bimetallic strip expands or contracts as the temperature changes, moving the dial or pointer up and down the temperature dial. The down side to these thermometers is that over time the bimetallic strip slightly bends and warps due to the constant changes in temperature. This requires the thermometer to be re-calibrated in order to stay accurate. You will notice a small nut usually at the base of the thermometer dial itself. This nut can be tightened to adjust the bimetallic strip to the right tension in order to keep expanding and contracting at the proper rate when heated and cooled.
Re-calibrating these types of thermometers usually involves a two-step process. Ideally, you would want to be at, or near sea level so that the pressure from the atmosphere doesn’t change the boiling point of water. Since we know that at sea level, water boils at 100C or 212F and freezes at 0C or 32F, we can use this information to help re-calibrate the thermometer to these pre-set temperature points.
How to Calibrate a Thermometer
To begin, you will need a pot of boiling water with at least 4 inches of water in it, and an ice bath. To make an ice bath to help calibrate a food thermometer, crush up ice cubes and place them in water until the whole bowl Is filled with an icy slush mixture… you want to get the temperature as close to 0C(32F) as possible.
When you submerge the thermometer into the boiling water (be careful not to touch the bottom of the pot with the thermometer as it will have a higher surface temperature than the boiling water) the thermometer should read 100C or 212F, if it doesn’t wait for the dial to stabilize and then adjust the nut to 100C(212F) . Let the thermometer come back to room temperature on its own so you don’t “shock” the metal before then placing it in the ice bath. When you submerge the thermometer in the freezing water bowl, the temperature should read 0C or 32F. If the pointer is off, again turn the nut under the dial until it does point to the correct temperature (0C or 32F). You will know that the thermometer is properly reset, once both these readings hit the proper temperature mark in either boiling or freezing water.
It is best to re-calibrate thermometers after they have been dropped, used very frequently or gone from a very high temperature to a very low temperature very suddenly.
When it comes to digital thermometers, (affiliate link) some can unfortunately not be calibrated by the method explained above, since they work through the use of an electric current. Digital thermometers measure the resistance of the electrical current as it travels through the metal probe. As the temperature changes, so does the resistance of the current, allowing for an accurate temperature reading on the display. Some digital thermometers may have a reset button, which you can press after the temperature has stabilized on the display while following the same procedure as above. For others, you may need to follow the manufacturer’s instructions to properly re-calibrate the thermometer.
In my personal home kitchen, I prefer to use digital thermometers, simply for the quick and accurate reading they will give you. If you take care of them and make sure not to drop the thermometer, you shouldn’t have any issues while using it. When choosing a thermometer, pick one where you can easily read the temperature display and (speaking from personal experience) don’t buy the very cheapest one, they are usually the ones that will need calibrating more often, and have a tendency to break! Hopefully you won’t have to go out and buy a new thermometer every time your current one is “broken”, like I did before learning how to properly calibrate a thermometer.
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