Time & Temperature

Remember from the video "Time & Temperature" are 2 of the 4 key conditions required for bacteria to multiply and survive. Understanding the key temperatures is very important to preventing the multiplication and survival of pathogenic bacteria.

The Germometer

The diagram below shows the key temperatures that are important for you to learn for food safety.

-18°C 

This is the legal minimum-maximum temperature the freezer should be. From -18°C and below pathogenic bacteria are dormant (sleeping) and do not multiply. At this temperature they are not dead they are just waiting for the right conditions to grow. (Remember warmth is one of the conditions bacteria need to multiply.)

TOP TIP: Checking your freezer temperatures in your work area twice daily will be part of your job role. When deliveries happen for frozen products, the delivery vehicle will be checked to make sure it is at least -15°C (the door opening will make the freezer vehicle to about -15° but not the food). Most freezers on board have alarms that alert when the temperature is below -18°C.

0°- 5°C

This is the legal temperature range of the food in the fridge. The cold of the fridge slows down the rate at which bacteria grows. We probe food in the fridge to make sure the core temperature is 5°C or less. However, it is ok if the digital display for the fridge reads 0°- 8°C. This takes into account the opening and closing of the door. 

TOP TIP:  To avoid cross-contaminating when probing your food in the fridge use a gel pack to probe instead. These are widely available and sit in your fridge all the time to allow you to check temperatures safely. Alternatively use a bacterial wipe on the probe before and after probing. 

Again the delivery vehicles of chilled food are checked and must not be over  8°C so you can be sure the food is safe. All your food fridges in galleys, behind bars, crew mess and pantries need to have temperatures checked twice daily and recorded. 

Again fridges on board have alarms that alert when the temperature is below 5°C.

It is important to note on board as well, that food arrives and is stored in a large central walk fridge and freezers. The food may then be moved elsewhere in the vessel to other preparation areas of galleys. The transfer time is just 15mins! It then must be stored in the fridge or freezer again or prepared quickly and cooked, or defrosted quickly, prepared and cooked.

5°- 63°C: 

This is the danger zone or high-risk zone. This is the range where bacteria grow rapidly with the most rapid growth being 20°-50° (think about the body core temperature of around 37°C). High-risk food (ready to eat) or raw food to be cooked must be kept out of this zone. So keeping preparation times to a minimum is important before cooking thoroughly or putting them back in the fridge. Food kept in the danger zone for 2 hours or more MUST be thrown away.

If you think about a high protein dish that is prepared, then cooked in advance, cooled and then reheated. This dish has gone through the danger zone 3 times. This increases the risk of bacterial multiplication, so is it better to cook and serve/eat straight away?

TOP TIP:  Always label any ready-to-eat food (high risk) with a time of display if held within the danger zone. An example of this is a cheese board. At room temperature it can only be displayed for 4 hours then the cheese must be discarded. Areas most at risk on board are buffets without temperature control (Hot and cold) or food left in the crew mess outside of the fridge for example. Keeping the amount of food displayed out of temperature to small plates and replenishing often will reduce waste.

63°C 

At 63°C most pathogens are starting to die (just above the danger zone). This is not the cooking temperature but is a very important temperature to learn for holding hot food during service as there is very slow multiplication above this temperature.  You can hold hot food for service in the crew mess or buffet stations above 63°C but only after thorough cooking. If you are holding food stir it frequently and probe test every 90 mins in the core of the food to make sure it is above 63°C.

TOP TIP: If you are holding food above 63°C make sure you make a note of the time you start displaying it and check the core temperature every 90 mins. Do not top up with fresh food, finish what is there and then replace it. 

75°C or above

This is the temperature most pathogens are dead and are now at a safe level and the food is safe to eat. This is the minimum cooking temperature unless you cook to 72°C for at least 2 minutes. 

100°C

Bacteria are killed at this temperature. This is the boiling point.

But it does not end there. Some pathogenic bacteria are very resilient and work hard to survive. They do this by forming spores. This is especially important to know when it comes to cooking, cooling and reheating food. The video in the next section explains spore formation. 

Toxins are poisons produced by some bacteria when they multiply and also when they die. Many are heat resistant and unaffected by freezing. They cause food poisoning with a short incubation period (time from eating to becoming ill). Toxins are produced when bacteria multiply, begin to die or start forming spores.

As you have now learnt cooking to 75°C or above is the most effective way of destroying bacteria (but not killing spores). It is however useful for you to recognise other ways food is treated to kill bacteria) or slow down multiplication. You do not need to have an in-depth knowledge of these processes.

Pasteurisation: (raw milk is pasteurised and fruit juices). Pasteurisation is a process where certain foods are quickly heated for a short time to kill bacteria that can make you sick. The temperature is relatively low for example raw milk is heated to 72°C for 15 seconds. Pasteurisation keeps foods safe and does not affect the nutrients found in foods. Spores and some toxins will survive pasteurisation so it's important that they are stored in the fridge.

Sterilisation: This is the destruction of all micro-organisms using higher temperatures exceeding 100°C. Examples of sterilised foods are canned fish, baby food in jars, canned or jarred vegetables, sauces in pouches, bottled milk, pet food in pouches, in trays, and baby food in pouches. The shelf life is prolonged but there can be a decline in the nutritional content.

UHT (Ultra Heat Treated): is a food processing technology that sterilises liquid food by heating it above 135 °C (275 °F) for 2 to 5 seconds. Foods include milk, milk products and soy/nut milk for example. The products will keep for several months without refrigeration.

Smoking: For example smoked fish and meat. Smoking is the process of flavouring, cooking, or preserving food by exposing it to the smoke from burning or smouldering plant materials like wood. Smoking of food is done at the commercial as well as the home level. The meats are hung or placed on racks in an enclosed area so that the smoke does not escape and instead penetrates foods. Commercial smoking is sometimes carried out with steam pipes that supplement the wood fire. Since smoke is antimicrobial and antioxidant it is used to preserve foods.

Vacuum Packing:  This process removes all the air out of the plastic packaging around the food and seals it. This slows down bacterial growth but anaerobic bacteria do not require oxygen so vacuum-packed food should be refrigerated.

Then of course there is the use of chemicals, acids and sugars to preserve food. Drying food by removing the water is useful for some products like milk and stocks for convenience and shelf life, but once rehydrated they must be treated like fresh products.