Thermometer Use and Calibration
- [Narrator] Thermometers are one of the most important food safety tools.
They are used to monitor temperatures when cooking or cooling foods as well as when storing foods in the refrigerator or on a heated tray.
It is important to understand how to properly calibrate and use thermometers in order to ensure that food temperatures are properly taken.
There are two main types of thermometers.
The dial or bi-metallic stem thermometer and the digital or instant read thermometer.
The bi-metallic stem thermometer is a mechanical thermometer which must be calibrated regularly.
A digital or instant read thermometer is electronic and cannot normally be calibrated.
Both types of thermometers can be used in a number of different applications.
They are used to measure the temperature in roasts, casserole trays and pots of stew or soup.
They can also be placed in refrigerated cases to check temperature.
When measuring the temperature of food with a bi-metallic thermometer, it must be inserted into the product up to the dimple mark in the stem.
You should insert the thermometer into the thickest part of the food and check in two locations to make sure the proper temperature has been reached.
Bi-metallic thermometers must be left in the food for at least 15 seconds before taking a final reading.
When purchasing a bi-metallic stem thermometer there a few things to look for.
First, the thermometer dial has a range that can measure from zero to 220 degrees Fahrenheit.
The increments or markings must be for every two degrees or less.
The thermometer must have a nut on the bottom for calibration.
While the digital instant read thermometers are generally more expensive than bi-metallic thermometers, they do have advantages.
They can read the temperature of foods quicker, normally within two to ten seconds.
They are also easier to use with thinner foods such as hamburgers or steak cutlets because the measuring zone is at the tip of the thermometer.
However, they do require changing batteries on occasion and can be easily broken if they are dropped or become wet.
To use a digital thermometer, turn on the unit and then insert the tip into the thickest part of the meat so that the tip is positioned in the center of the item being measured.
Again, take the temperature in two locations.
As already stated, the bi-metallic stem thermometer should be calibrated regularly.
It should be done as often as each day and should be done anytime the unit is dropped or twisted.
There are two simple ways thermometers can be calibrated.
The ice water method or the boiling water method.
These methods can also be used to check the accuracy of a digital thermometer.
Thermometers for use in food applications should be accurate to plus or minus two degrees Fahrenheit.
To use the ice water method, fill a large glass with crushed ice to the top and add water to fill the glass then stir to combine.
Wait about minute before inserting the thermometer stem into the center of the glass.
Take care not to touch the sides or bottom of the glass.
Wait 15 to 30 seconds and read the temperature on the thermometer.
The thermometer should read 32 degrees Fahrenheit or 0 degrees Celsius.
If the thermometer does not read 32 degrees, it must be calibrated.
To do this, leave the thermometer in the ice water.
And using a small wrench or pliers, turn the calibration nut located underneath the thermometer's dial.
Adjust the reading on the gauge by using the wrench to rotate the dial head either left or right until the dial reads 32 degrees Fahrenheit.
To use the boiling water method, bring a pot of water to a roiling boil.
Insert the thermometer into the boiling water.
Again, take care not to touch the side or bottom of the pot.
Wait 15 to 30 seconds and read the temperature of the thermometer.
It should read 212 degrees Fahrenheit.
To calibrate, leave the thermometer in the boiling water and using a wrench or pliers, turn the calibration nut underneath the thermometer's dial.
Adjust the reading on the gauge by turning the dial head either left or right until the dial reads the correct temperature of 212 degrees Fahrenheit.
Please note, elevation will affect the temperature at which water boils.
As elevation increases, the boiling point of water decreases.
Check the website provided for the elevation of your location.
Generally a digital thermometer can not be calibrated.
But you should occasionally check the accuracy using either the ice water or boiling water method of calibration.
Remember that thermometers come into contact with food so be sure to clean and sanitize your thermometer after each use.
Wash with soap and warm water and dip in a sanitizing solution or wiped with an alcohol pad.
Thermometers should be stored in a secure location when not in use.
A broken thermometer can be a physical hazard in the food.
When purchasing digital or bi-metallic thermometers, look for the NSF mark.
This indicates that the thermometers have been approved for use in food service operations.
Thermometers are an important tool for ensuring the safe preparation and handling of food.
Choose the thermometer which bets fits your needs.