FSA Explains: The science behind our Christmas advice

turkey cooked in the oven


Cross-contamination is what happens when bacteria or other microorganisms are unintentionally transferred from one object to another.

The most common example is bacterial transfer between raw and cooked food – this is thought to be the cause of most cases of foodborne infections. For example, when you’re preparing raw chicken, bacteria can spread to your chopping board and knife. If you then use the same board and knife to prepare a ready-to-eat product such as bread, this could cause food poisoning. That’s why it’s so important that you either use separate knives and chopping boards, or wash them thoroughly between tasks.

Cross-contamination can also happen when you wash raw turkey and that's why we advise against it.

The ‘Danger Zone’

We advise that the safest way to defrost food is in the fridge overnight. Bacteria will grow at temperatures above 8°C and below 63°C; this is known as the ‘Danger Zone’ for microbial growth. By defrosting in the fridge, which should ideally be at 5°C or below, the food should never enter the ‘Danger Zone’. Some bugs such as listeria monocytogenes can grow at lower temperatures than 8°C.


Cooking methods

Food cooked in an oven cooks through three heat transfer methods:

  • Radiant or direct heat, where the flames at the back of a gas oven or the element in an electric oven cook the food.
  • Conduction, where the heat travels through the shelf, into the baking tray / dish and then into the food.
  • Convection, where the air within the oven is heated and travels over and through the food (particularly important in fan-assisted ovens – this is why they cook food faster).

If the bird is stuffed, the convection cooking method is severely hampered. That’s why we advise that birds be cooked unstuffed, with any stuffing cooked in a separate tray or dish.

Different cooking times for poultry

We advise that you cook geese and ducks at higher temperatures than chicken. This is in order to help render the fat. Unlike chickens, ducks and geese are waterfowl and have a thick layer of fat under the skin to keep them warm and aid their buoyancy. To remove this, the birds must be cooked at higher temperatures.