1. Food Thermometers Calibrating Instant-Read Bi-metallic Thermometers
Adapted from a presentation prepared by
Hospitality & Tourism Management
Purdue University

2. Bi-metallic Stemmed Thermometers
The most common and versatile type
Measures temperature through a metal probe with a sensor at the end
Usually measure from 0°F to 220°F
50F to 550F NOT practical
Must be capable of re-calibration
Must have an adjustable nut
Adapted from Purdue University, Hospitality & Tourism Management

3. Bi-metallic Stemmed Thermometers
When selecting this type of thermometer, it should have:
An adjustable calibration nut
Easy to read numbered temperature markings
A dimple to mark the end of the sensing area
Accuracy to within ± 2°F (± 1°C)
Adapted from Purdue University, Hospitality & Tourism Management

4. Rules For Using the Thermometer
Keep the thermometer and its case clean
Wash, rinse, sanitize & air dry after every use
When measuring an item,
insert probe through the thickest part of the item
insert deep enough to pass the dimple or sensing area of the thermometer
Calibrate regularly to insure its accuracy
Adapted from Purdue University, Hospitality & Tourism Management

5. Adapted from Purdue University, Hospitality & Tourism Management
When to Calibrate --
After dropping the thermometer
If shocked by extreme temperature change
Periodically, depending on frequency of use.
Adapted from Purdue University, Hospitality & Tourism Management

6. Calibrating the Thermometer
There are two basic acceptable methods
Ice-Point Method
Boiling-Point Method
Adapted from Purdue University, Hospitality & Tourism Management

7. Ice-Point Calibration Method
Fill a large glass with crushed ice
Add tap water to fill glass, stir well
Place stem into the ice water
sensing area must be completely submerged and not touching the glass
Wait at least 30 seconds
until the indicator stops moving
Adapted from Purdue University, Hospitality & Tourism Management

8. Ice-Point Calibration Method
With the thermometer stem still in the water
Hold calibration nut secure with pliers/wrenche
Carefully rotate thermometer head
Until the pointer reads 32°F
__________________
(The plastic case that comes with some models has a “hex-hole” built-in - to use instead of a pliers or wrench.)
Adapted from Purdue University, Hospitality & Tourism Management

9. Ice-Point Calibration Method
Adapted from Purdue University, Hospitality & Tourism Management

10. Boiling-Point Calibration Method
Bring clean water to a boil in a deep pan
Place the thermometer stem into the boiling water
sensing area must be completely submerged and not touching the glass
Wait at least 30 seconds
until the indicator stops moving
NOTE: only use for thermometers that start reading above 32°F
Adapted from Purdue University, Hospitality & Tourism Management

11. Boiling-Point Calibration Method
With the thermometer stem still in the water
Hold calibration nut secure
Carefully rotate thermometer head
Until the pointer reads 32°F
the thermometer head so that the pointer reads 212°F
__________________
(The plastic case that comes with some models has a “hex-hole” built-in - to use instead of a pliers or wrench.)
Adapted from Purdue University, Hospitality & Tourism Management

12. Boiling-Point Calibration Method
Adapted from Purdue University, Hospitality & Tourism Management