Published on 12/17/02

Calibrate food thermometer before Xmas cooking

By April Reese
University of Georgia

Be sure your Christmas dinner is properly cooked. Calibrate your food thermometer so the reading is accurate.

Elizabeth Andress, an extension service food safety specialist with the University of Georgia College of Family and Consumer Sciences, warns cooks of the risks associated with an inaccurate thermometer.

"Be sure to calibrate your thermometer before checking temperatures, or they don't mean anything," Andress said.

There are two ways to check the accuracy of a food thermometer, she said. The preferred method uses ice water, the other boiling water. Many food thermometers have a calibration nut that can be adjusted.

Method 1: ice

Andress suggests using an ice-water slush to calibrate your thermometer. "The ice method is a much easier process to manage than boiling water and very accurate no matter where you live," she said. "Boiling temperatures will vary with altitude."

She lists five easy steps that can make your holidays safer.

  1. Make a 50/50 ice and water slush — at least half ice. The more ice the better, but you need water to fill in all the air spaces around the pieces of ice. Make it deep enough to stick the whole sensing area (tip) of the thermometer into the middle of it.
  2. Immerse the thermometer stem into the slush, making sure the tip doesn't touch the container side or bottom.
  3. Wait until the temperature reading stops changing. This may take 5 to 10 minutes. Once you think it has stopped, make sure it stays the same for 3 full minutes.
  4. The temperature should read 32 degrees F. If it doesn't, turn the calibrating nut under the dial or face until it does read 32.
  5. Clean and sanitize the thermometer and its case before using to check food temperatures.

Method 2: boiling water

The United States Department of Agriculture suggests boiling water as an alternative method for checking accuracy.

  • Bring a pan of clean tap water to a full rolling boil.
  • Immerse the stem of a food thermometer in the boiling water, at least 2 inches, and wait at least 30 seconds. Make sure the reading on the thermometer isn't still changing.
  • Without removing the stem from the boiling water, hold the adjusting nut tightly in place under the head of the food thermometer with a suitable tool and turn the dial head so the thermometer reads 212 degrees F.
The boiling method may not read accurately due to varied atmospheric conditions.

"Remember that water boils at a lower temperature in a high altitude," Andress said. "Check with the local Cooperative Extension Service or health department for the exact temperature of boiling water in your area."

If you have a food thermometer that can't be calibrated, it's still important to check it for accuracy.

"Small inaccuracies should be taken into consideration when using the food thermometer," Andress said. "Replace the thermometer if it's more than a few degrees off."

For example, water boils at 212 degrees, so if the thermometer reads 214 degrees, it's 2 degrees too high. So when you're cooking ground-beef patties, which must reach 160 degrees, add 2 degrees and cook the patties to 162 degrees.

Digital food thermometers don't have a calibration nut under the head. But their accuracy should still be checked by one of these methods.

Some digitals have a means of calibration described on their package. If they can't be calibrated, try changing the battery. If that doesn't make them read accurately, replace the thermometer.

More information

For specific information on how to calibrate or use your food thermometer or on recommended safe food temperatures, call your UGA Extension Service county office (a href=" countydistrict.cfm"> countydistrict.cfm). Or call the toll-free USDA Meat and Poultry Hotline (1-800- 535-4555) from 10 a.m. to 4 p.m. (or e-mail