Calibrating thermometers

1. Place some ice into a container with a small amount of cold water. The ice should not float if the right amount of water is used.
2. Mix into a slurry and insert the thermometer probe.
3. Leave it for about 3 minutes.
4. Check and note the temperature. It should read 0°C.
5. Do this 3 times and compare the temperatures recorded. If they vary by more than 1°C, the thermometer should be replaced or serviced.

1. Bring a saucepan of water to a continuous rolling boil on a stove.
2. Insert the thermometer probe and leave it for about 3 minutes.
3. Check and note the temperature. It should read 100°C (unless in an area of high altitude – see ‘Calibration in varied altitudes’ below).
4. Do this 3 times and compare the temperatures recorded. If they vary by more than 1°C, the thermometer should be replaced or serviced.

Some thermometers may come with a mechanical calibration unit. If so, follow the manufacturer’s directions on calibrating your thermometer. You may also be able to return your thermometer to the manufacturer. 

Australian mountain ranges do not have sufficient height to cause the problems in cooking seen on Everest or in Colorado due to reduced boiling points but they are high enough to interfere with thermometer calibration.

Water will boil at temperatures around 94°C at the highest towns in NSW, so if the expectation is 100°C, thermometers appear to exceed the +/- 1°C tolerance.  

Those calibrating thermometers and undertaking internal and external audits should note the reduced boiling point of water at higher altitude towns in the table below.

Table 1: Approximate boiling point of water for higher towns in NSW. 

Table 2: Boiling point of water at varying altitudes

Once the handheld thermometer is calibrated it can also be used to check the accuracy of any temperature gauges on equipment, such as coolrooms and freezers. This should be done at least 6 monthly.  

• Place the thermometer in the coolroom/freezer, with the thermometer probe placed as close to the gauge probe as possible, for at least 5 minutes (making sure not to open the door during this period).
• After this period, read the temperature on the thermometer (taking into account any difference noted during the calibration of the handheld thermometer).
• Read the temperature on the gauge and determine any difference between the handheld thermometer reading and the gauge, as above.
• Be sure to clean and sanitise the thermometer before taking the temperature of food. 

Prior to taking the temperature of food, thermometer probes must be cleaned, and then sanitised.

• Clean off any food waste or other visible contamination.
• Wash and dry the probe with warm water and detergent.
• Sanitise using an appropriate food grade sanitiser (for example, an alcohol wipe) or water 77°C or hotter for at least 30 seconds. Follow the manufacturer's instructions.
• Air dry or use a single-use towel.
• Insert the probe into the centre or thickest part of the food. For packaged products, place the probe between two packages.
• Read the temperature (and record it if applicable).

Always remember to:

• put the probe into the thickest part or the centre of the food  
• wash and sanitise the probe between every reading
• store the probe where all staff can access it
• make sure the thermometer is calibrated regularly
• fix the problem if food is not at the required temperature, for example, continue to heat it or throw it out.