Monitoring temperatures

Monitoring temperatures

Cabinet thermometer readings should be checked regularly, using an accurate digital or infrared thermometer, and recorded at least twice a day. Indicating or recording thermometers are essential and premises with a large number of units will need automatic monitoring equipment and alarms to warn of unacceptable temperatures. If readings indicate air temperatures above prescribed limits, then the temperature of a food simulator or between-pack temperatures should be taken. If concern remains then probing of the food should be undertaken.

Many food businesses will maintain detailed temperature records, either written or on data logger printouts. For small catering or retail units that keep daily diary it may be sufficient just to record any problems and corrective action taken, fro example, in the event of a refrigerator breakdown. It will be necessary to verify or confirm that temperature monitoring has been carried out correctly. One method of verification of temperature records will be as part of planned audits of food safety procedures. Accurate temperature records may contribute to a due-diligence defence.


Using digital probe thermometers

The use of accurate, tip-sensitive thermometers is the best way to check the temperature of cold or hot food. Probes must be cleaned and disinfected before and after use to remove the risk of microbiological and allergenic cross-contamination. Probes should be cleaned before using disinfecting wipes and a contact time of 30 seconds is recommended. Alternatively, hot water above 82°C may be used to disinfect the probe. To ensure probes are accurate, they should be validated (calibrated) weekly/monthly depending on use. Validation involves using melting ice, when the temperature should read 0°C, and boiling water, when the temperature should read 100°C. Alternatively, test caps may be used. An error of plus or minus 1°C is acceptable. Common mistakes involving the us of probe thermometers include:

  • failing to clean and disinfect before use;
  • not allowing sufficient time for an accurate reading;
  • not taking the core temperature;
  • not using a calibrated thermometer;and
  • taking a false reading because the probe is touching a bone or the side of a container.

Infrared themometers

Infrared thermometers, which work by measuring the amount of radiant energy, can be used to scan foods very rapidly. Any identified problems can be checked immediately with a digital thermometer. Additional advantages include the fact that it is non-destructive testing and there is no risk of cross-contamination. It is particularly useful for scanning retail cabinets, frozen food, deliveries and dispatch as large consignments can be checked for hot spots.

Temperature data loggers

Data loggers and printers will provide a variety of useful information about refrigerated storage including current temperature, maximum, minimum and trends of temperature over a specified period. Should temperatures rise above a predetermined level they can also trigger an alarm.


 Cooking is used to make food palatable and safe for immediate consumption. Core temperatures of 75°C are usually adequate to destroy food poisoning bacteria although some preformed toxins and spores will not be destroyed. Lower temperatures for longer times may be equally effective. A disinfected digital probe thermometer should be used to check correct core temperatures have been achieved, especially for poultry and rolled joints. Colour and texture changes ( no pink buts), and ‘juices of poultry running clear’ are useful indicators of correct cooking.

Cooked food should, unless it is immediately cooled, be kept hot at or above the legal temperature of 63°C or served for immediate consumption. This temperature prevents the germination of spores or the multiplication of bacteria. Hot food on display in a buffet is allowed to fall below 63°C for a maximum period on one occasion of up to 2 hours.

Microwaves are often used for cooking and reheating food. The main advantage is that cooking is quick. However, there is a danger of cold spots, if manufactures instructions are not followed. Bacteria will survive in these cold spots.

If bloody chicken is served to a customer this indicates under cooking. The chicken should be replaced and action taken to prevent recurrence. The usual could be inadequate cooking time for the size of the chicken or a defective oven. Regular maintenance of the oven will reduce the likelihood of this latter problem. The temperature of the chicken should be checked after cooking to ensure 75°C or equivalent has been achieved.