28 5.2: Thermometer Maintenance
5.2 Thermometer maintenance
Thermometers are very useful in helping TCS foods remain safe. However, thermometers if not properly maintained can cause harm. It is important that the probe or stem of a thermometer is cleaned and sanitized before use, during usage when moving between TCS foods, and after use. Cross-contamination is possible when the thermometer is exposed to food or a surface that can introduce pathogens to another food or surface. It is recommended that the thermometer be kept in its sheath or cover while not in use. Additionally, all manufacturer care instructions for your thermometer should be followed.
Less commonly used in kitchens currently are glass thermometers for candy making and deep fat frying. When used it is essential that they have a shatterproof casing as broken glass can become a physical contaminant.
Thermometer calibration
Due to the important role thermometers play in keeping food safe, it is critical that thermometers are consistently accurate in their temperature readings. In order to keep thermometers accurate, they need to be calibrated. Calibration is the process of getting a thermometer reading to an established baseline temperature in order to ensure accuracy. For measuring food temperature, thermometers must be within +/- 2 ℉ or +/- 1℃. When measuring the air temperature in a piece of equipment, the thermometer must be accurate to +/- 3℉ or +/- 5℃.
Any thermometer that cannot be calibrated by the user should be taken out of service, or returned to the manufacturer for calibration.
When to calibrate your thermometer
Thermometers should be calibrated regularly, especially at the following intervals:
At the start of a new shift
After being dropped or bumped
After moving between hot to cold or cold to hot items
How to calibrate your thermometer
Thermometers can be calibrated by one of two methods: ice-point method or the boiling-point method. Water freezes at 32℉( 0℃). When placed in icy water, the thermometer read out should be 32℉( 0℃). Water boils at 212℉(100℃). When placed in boiling water, the thermometer should readout 212℉(100℃). The chart below demonstrates how each method works.
While both calibration methods are permissible, the ice-point method is used more often than the boiling-point method because it is considered safer and easier. Bimetallic thermometers have a calibration nut located on the underside indicator head. This is what is adjusted to get the proper read out. To calibrate the thermocouple or thermistor thermometer, follow the manufacturer instructions. Also note that the boiling point of water can vary based on your area’s elevation. Please check the boiling point of water for your area and use that temperature as your baseline.
Taking Food Temperatures
Now that we have established the proper thermometer to use, when & how to calibrate a thermometer and the critical limits for accuracy, it is time to actually check food temperature. To take the temperature of a food item the stem or probe should be inserted into the thickest part of the item ensuring that the probe or stem is not touching the food storage container or bottom of the cooking surface. Once placed, allow the indicator time to settle before recording the temperature. The best practice is to allow for 15 seconds to pass for both digital and analog readings. It may also be useful to check the temperature of another area of the food item to double-check for consistency.