How to Test and Calibrate a Cheesemaking Thermometer
An inaccurate thermometer can affect your rennet, cultures, curd texture, and final cheese. Learn how to test and recalibrate an analog metal probe thermometer or check if any thermometer is inaccurate using a simple ice slurry or boiling-water test.
If your cheese is not setting properly, your curds seem unusually soft, or your milk heats much faster than expected, your thermometer may be giving you an inaccurate reading.
Temperature matters throughout cheesemaking. A thermometer that reads 60°F when the milk is actually 110°F can dramatically affect the rennet, cultures, curd texture, and final cheese.
Fortunately, an analog metal probe thermometer may not be broken. It may simply need to be recalibrated.
First, Check What Kind of Thermometer You Have
These instructions are for an analog metal probe thermometer with a round dial.
Look for a small calibration nut directly underneath the dial. If your thermometer has this nut, you can usually adjust the needle with a small wrench or pair of pliers.
Some analog thermometers are not adjustable. Digital thermometers require a different troubleshooting process and usually cannot be recalibrated by turning a nut. The manufacturer will provide instructions but you can check accuracy with these same methods.
The Best Method: Test It in an Ice Slurry
An ice-water slurry provides a reliable known temperature of 32°F or 0°C.
You Will Need
- A drinking glass or small container
- Plenty of ice
- Cold water
- Your thermometer
- A small wrench or pair of pliers, if adjustment is needed
How to Test Your Thermometer
- Fill the glass completely with ice.
- Add enough cold water to fill the spaces between the ice cubes.
- Stir the mixture and let it sit for about one minute.
- Insert the thermometer probe at least two inches into the center of the ice slurry.
- Do not allow the probe to touch the bottom or sides of the glass.
- Wait about one minute, or until the needle stops moving.
The thermometer should read 32°F or 0°C, or very close to it.
A difference of one or two degrees is usually not a concern for home cheesemaking. A larger difference means the thermometer should be adjusted or replaced.
How to Recalibrate an Analog Thermometer
Keep the thermometer probe in the ice slurry.
Use a small wrench or pair of pliers to hold the calibration nut underneath the dial. Turn the nut slowly until the needle points to 32°F or 0°C.
The dial may move as you turn the nut, so work slowly and check the reading again before removing the thermometer.
Once adjusted, repeat the ice-slurry test to confirm that the thermometer now reads correctly.
You Can Also Test It in Boiling Water
No ice available? You can test your thermometer in boiling water.
- Bring a pot of water to a full rolling boil.
- Insert the probe at least two inches into the water.
- Keep the probe suspended in the water without touching the bottom or sides of the pot.
- Wait until the needle stops moving.
At sea level, the thermometer should read approximately 212°F or 100°C.
Keep in mind that water boils at a lower temperature at higher elevations. For that reason, the ice-slurry method is usually the simplest and most dependable test.
Use caution around boiling water and hot steam.
What If the Needle Does Not Move?
Your thermometer may need to be replaced if:
- The needle remains stuck
- The reading changes unpredictably
- The thermometer cannot hold a steady reading
- The probe or dial is damaged
- The dial contains moisture or condensation
- The thermometer is more than a few degrees off and cannot be adjusted
- The calibration nut turns but the needle does not respond
Test More Than One Temperature When Possible
A thermometer can read correctly at 32°F but become less accurate at cheesemaking temperatures.
After calibrating it in ice water, compare it with another trusted thermometer in warm water between 85°F and 115°F, the range commonly used for many beginner cheeses.
If the two thermometers consistently disagree by several degrees, replace the less reliable one.
How Often Should You Test Your Thermometer?
Test your thermometer:
- Before an important cheesemaking project
- If a cheese behaves differently than expected
- After the thermometer has been dropped
- If the dial has been bumped or twisted
- Every few months if you make cheese regularly
A quick thermometer check can prevent wasted milk and eliminate one of the most common causes of confusing cheesemaking results.
Keep Learning
A dependable thermometer is only one part of a successful batch. These guides can help you avoid two other common cheesemaking problems:
How to Test Your Rennet Before Making Cheese
Make sure your rennet is still active before you risk a full gallon of milk.
How to Choose the Best Milk for Cheesemaking
Learn which milk labels to look for, which ones to avoid, and why some milk forms better curds than others.
Ready to build your cheesemaking skills one manageable cheese at a time?
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