Food temperature and thermometers

The food safety standards specify that potentially hazardous foods must be stored, displayed and transported at safe temperatures and, wherever possible, prepared at safe temperatures. However, you can also use time, rather than temperature, to keep food safe. This method is explained under 'The 2 hour/4 hour guide'.

Safe temperatures are 5°C or colder, or 60°C or hotter. Potentially hazardous food needs to be kept at these temperatures to prevent food-poisoning bacteria, which may be present in the food, from multiplying to dangerous levels. These bacteria can grow at temperatures between 5°C and 60°C, which is known as the temperature danger zone. The fastest rate of growth is at around 37°C, the temperature of the human body.

The food safety standards also require you to have a thermometer if you prepare, handle or sell potentially hazardous food. This will enable you to check that food is being kept at safe temperatures.

What foods are potentially hazardous?

Foods normally considered to be potentially hazardous are:

• raw meats, cooked meats and food containing meat, such as casseroles, curries, lasagne and meat pies
• dairy products and foods containing dairy products, such as milk, cream, custard and dairy-based desserts
• seafood (excluding live seafood) and food containing seafood, such as seafood salad
• processed fruits and vegetables, such as prepared salads and ready-to-eat fruit packs
• cooked rice and pasta
• processed foods containing eggs, beans, nuts or other protein-rich food, such as quiche and soya bean products
• foods that contain any of the above foods, such as sandwiches, rice salads and pasta salads.

Keeping food cold

When you are preparing food, make sure that you have enough refrigerator space or insulated boxes with ice bricks to store the food. It is important to remember that refrigerators do not work properly when they are overloaded or when food is packed tightly, because the cold air cannot circulate. Refrigerated food needs to be 5°C or colder to keep it safe.

If you are running out of room in your refrigerator, remove foods that are not potentially hazardous, such as soft drinks. The temperature of these foods is not critical and they can be kept cool in insulated containers with ice or ice blocks.

If you are transporting cold potentially hazardous food, keep it cold with insulated bags or boxes and ice bricks.

Cooling cooked foods

If cooked potentially hazardous food needs to be cooled to use later, its temperature should be reduced quickly to keep it safe. The cooling needs to happen in two stages to be sure the food is safe. First, the food's temperature must fall from 60°C to 21°C in less than two hours. Next, the food needs to cool further from 21°C to 5°C or colder within the next four hours. It is difficult to cool large volumes of food within these times unless you put the food into smaller portions or shallow containers.

Please note this 2-stage cooling process is separate to the 2 hour/4 hour guide below. If you have cooled food according to the 2-stage process, it is safe to store in the fridge to use later. If you then bring the food out of refrigeration, the clock 'starts again' and you can follow the 2 hour/4 hour guide.

Keeping food hot

If you are keeping food hot on cooktops, in ovens or in bain marie units, the equipment needs to be set high enough to ensure the food remains hot (60°C or hotter will ensure it is safe).

If you are transporting hot food, it needs to be kept hot, for example using insulated bags and hot packs.

If you are displaying food to serve within a short period (e.g. at a temporary stall), it is safe to use a temperature lower than 60°C if the food is used or sold within 4 hours. After that time it needs to be thrown out.

The 2 hour / 4 hour guide 

Potentially hazardous food should be kept at 5°C or colder or 60°C or hotter wherever possible to be sure it is safe. However, it is not always practical to do this, for example during food preparation, delivery or display. The food can be held safely between 5°C and 60°C for short periods - generally for less than four hours. This is because it generally takes more than four hours for food-poisoning bacteria to grow to dangerous levels. After four hours the food needs to be discarded.

The 2 hour/4 hour guide applies to ready-to-eat potentially hazardous food brought out of refrigeration. It provides guidance on how long this type of food can be held safely at temperatures between 5°C and 60°C and what should happen to it after certain times. The times include all time out of the fridge, so remember to add up the total time the food has been between 5°C and 60°C (e.g. time taken for sandwich preparation and display).

Why have a thermometer?

A thermometer is essential for ensuring food is kept at safe temperatures. If your organisation prepares, handles or sells any potentially hazardous food, it must have a thermometer accurate to ±1°C. This means when the thermometer shows a temperature of 5°C, the actual temperature will be between 4°C and 6°C. The thermometer needs to be available for use when foods are being prepared, stored, transported or displayed, so you may need more than one if foods are handled in different places.

How to clean and sanitise your thermometer

As the probe of the thermometer will be inserted into food, the probe must be cleaned and sanitised before it is used to measure the temperature of the food. This is especially important when the thermometer is used to measure the temperature of raw food and then ready-to-eat food, for example raw chicken and cooked chicken. To clean and sanitise your thermometer:

• wash the probe to remove any grease and food particles;
• sanitise the probe using alcohol wipes or very hot water; and
• thoroughly dry the probe using a disposable towel or let it air dry.

Checking temperatures of food

• Determine the warmest area of a coolroom or the coldest area of a hot display unit.
• Insert the clean, dry probe into the food.
• Remember that temperature readings are not instant - wait until the temperature has stabilised before reading.
• Stabilise the thermometer between measuring hot and cold foods by allowing the thermometer to come back to room temperature.
• If the food is packaged or frozen, place the length of the probe between two packages of the food.

Remember that the temperature at the centre or thickest part of food might be different from the surface temperature. For example, when cooked food is being cooled in the refrigerator, the centre of the food will take the longest to cool. So, when checking the temperature of this food, make sure that you check its centre.

How to check the accuracy of your thermometer

Thermometers have to be accurate to ensure that temperatures are correctly measured. Ask the company that supplied your thermometer how often the thermometer should be checked for accuracy. It is best to have your thermometer regularly checked and maintained by the supplier of the thermometer. However, if you would like to check the accuracy of your thermometer yourself, use the following method.

• 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.
• Mix into a slurry and insert the thermometer probe.
• Leave it for about three minutes.
• Check and note the temperature. It should read 0°C.
• Do this three times and compare the temperatures recorded.
• If they vary by more than 1°C, get your thermometer checked by the supplier.