Guide to home refrigeration and the correct storage of cooked and fresh food items.
It is fair to say that our everyday lives would be completely different if someone had not invented the refrigerator. We would have to spend a lot more of our time in the kitchen and a considerable amount of our time shopping for food.
The refrigerator is a machine that keeps our food cold, at a temperature where bacteria grows at a minimal rate, and therefore preserves our food for much longer.
Before the refrigerator was invented people used to keep food cold in cellars or in underground caves lined with snow or ice (if available). Otherwise, food was preserved using other methods such as smoking, salting, pickling or drying. Most of these methods of food preservation have been around since the time of the Roman Empire or before.
How a refrigerator works
The main function of the refrigerator is to keep fresh and perishable foods from spoiling as quickly due to the rapid growth of bacteria. This is attained when food is kept at a temperature that is lower than 40°F (4°C).
Without a refrigerator fresh milk would perish within hours, as would fresh meat or fish, if kept at room temperature.
A refrigerant gas such as ammonia or chlorofluorocarbon (CFC) is compressed and cooled so that it turns into a liquid. The liquid is then evaporated, a process that requires energy or heat from the surrounding area. The heat is drawn from the inside of the refrigerator, which thus loses energy, therefore decreasing the temperature inside that area. The whole process then starts again once the liquid becomes a gas and this is how the temperature of the refrigerator is maintained.
The normal temperature of a refrigerator is between 1°C - 5°C (-34°F - -41°F). Anything lower than this and it would be too cold and cause the contents of the fridge to freeze, whilst anything higher would mean that bacteria would multiply quicker and food would get spoilt faster.
The coldest area of the fridge is at the top, just under the chill tray or the freezer section and the warmest area is at the bottom, in the crisper drawers where vegetables should be stored and on the inside of the fridge door.
The refrigerator door should be kept closed at all times and should only be kept open for the shortest amount of time possible. Leaving the fridge door open or frequently opening and closing it will cause the temperature inside to rise, as warm air is being drawn in all the time, therefore making the fridge work harder and use up more energy and electricity to lower the temperature back down to where it should be.
Bacteria and food
There are different types of bacteria that can contaminate food but not all lead to illness.
Spoilage bacteria result in the deterioration of the appearance, texture and smell of a food after a certain amount of time. This usually occurs in fruit and vegetables such as when an apple starts to get soft and bruised or a carrot dries out and becomes soft, limp and discoloured.
Looking at a piece of fruit or a vegetable that is deteriorating may not be very appealing and you would probably not want to eat that item of food either. However, if you did, you would not become ill.
On the other hand, if you ate food that had been contaminated with other types of bacteria, such as Salmonella, it would be a different matter.
Many foods contain a small amount of bacteria when you buy them, which could have appeared through any of the processes of slaughtering, harvesting, packaging, shipping or transporting.
The most susceptible foods to contamination from harmful bacteria are raw meat and poultry, fresh fish and seafood and some vegetables. The bacteria are usually destroyed through the cooking process but only if the food is cooked through for long enough at a high enough temperature.
The temperature at which bacteria is destroyed varies from food to food. For example a whole chicken must be cooked to an internal temperature of 180°F (82°C) but beef steaks and lamb chops will only need to reach a temperature of 145°F (63°C) for all bacteria to be killed.
Bacteria such as Salmonella and E. Coli thrive between the temperatures of 40°F - 140°F (5°C - 60°C). This means that if perishable food is kept between these temperatures for a long period of time, the bacteria on the food will multiply rapidly, often to dangerous levels within a few hours. If this is food is eaten it can lead to food poisoning, illnesses and in extreme cases, hospitalisation or death.
Fresh meat, poultry, fish and seafood should be refrigerated as soon as possible after purchase and should never be left outside of the refrigerator at home.
As soon as food is refrigerated and kept at a temperature below the "dangerous zone", the growth of the harmful bacteria is minimal and the risk of contamination leading to illness is greatly reduced.
Refrigerating leftover cooked food
Just as it is vital to refrigerate fresh meat and poultry as soon as possible after purchase, it is just as important to refrigerate leftover cooked dishes, especially if they contain meat, poultry, fish, seafood, eggs, rice or cooked vegetables as soon as possible after preparation.
Whilst food is left out to cool before refrigeration, bacteria can multiply and contaminate the food, especially if left out for too long and in warm weather. It is therefore important to reduce the temperature of the food quickly.
Nowadays many refrigerators can cope with warm or hot food being placed inside shortly after preparation.
However, it is always best to reduce the temperature of the leftover cooked food as quickly as possible by dividing it into portions and storing it in shallow, airtight containers. When placed in the refrigerator these smaller portions will cool down much faster.
Cooked meat, poultry or shellfish can be wrapped tightly in cling film or aluminium foil to prevent drying out or moisture loss.
When reheating leftover food, ensure that it reaches a temperature of at least 140°F (60°C) so that any bacteria can be destroyed.
Where to place certain foods in the refrigerator
It is always a good idea to organise the contents of your fridge properly so that you know where everything is. This means that when you open the refrigerator door to remove an item, you can go exactly to that place, grab the product and immediately close the door, thus saving time, electricity and money.
Although your fridge may be tidy and organised, do you know exactly where certain foods should be stored for maximum shelf life and safety? Below are guidelines for the correct placement of certain foods in the refrigerator in order to ensure the above.
- Firstly, do not overfill the shelves of your refrigerator, as this can prevent the circulation of cold air flowing all around, leaving some products at a slightly higher temperature than they should be.
- Keep similar foods together on the same shelf, so you know where to look for them.
- Store small items, yoghurts, butter, cheese, dips, small desserts and snacks on the top shelf at eye level.
- Place any cooked foods and leftover dishes above raw meat, poultry or seafood.
- Store all raw meat, poultry, fish and seafood products on the bottom shelf of the refrigerator. Leave these products in their original packaging and also place inside a plastic bag to prevent any leaking juices dripping on other foods.
- Store fruit and vegetables separately. Vegetables should be stored in the warmest part of the refrigerator (bottom drawers), as they require a storage temperature of about 50°F (10°C). (For more information see our guide to shelf life of food).
- Do not store eggs in the egg trays on the inside of the refrigerator door. The temperature here is higher than other parts of the fridge and fluctuates with frequent door opening. Keep eggs in their original carton and place near the top of the fridge.
- Store fruit drinks, bottled drinks, products in jars, sauces, condiments and generally products with a longer shelf life on the shelves and in the compartments on the inside of the refrigerator door.
- Ensure that all bottles and jars are closed and that all opened products are tightly wrapped in cling film or aluminium foil in order to prevent the food from drying out, spoiling or passing on odours to other foods.
Defrosting frozen products in the refrigerator
Frozen products should never ever be left out on the counter to defrost at room temperature, nor should they be submerged in warm water either. Either of these could lead to contamination by harmful bacteria due to the food being left at temperatures at which bacteria thrive and rapidly multiply.
The safest way to defrost food is by leaving it inside the refrigerator, preferably wrapped in a plastic bag if dealing with frozen meat, poultry, fish or seafood or with a plate underneath the product to contain thawed water and any leaking juices from the food.
Defrosting large joints of meat or a whole chicken or turkey requires a lot of time and therefore careful planning is needed to make sure that the item has defrosted completely by the time you need to cook it.
Most products will defrost completely if you leave them in the refrigerator overnight.
Looking after your refrigerator
As well as taking care of the food that you store your refrigerator in order to make sure that it lasts for as long as possible, you should also look after your fridge. If your fridge is clean and safe, your food will also be the same.
You should regularly clean your refrigerator. Clean your fridge on a day when it is looking a bit empty, so that you do not have to remove loads of different items and try to store them all safely during cleaning.
Place perishable goods in the freezer to keep them cold but fruit and vegetables may be left out at room temperature.
Whilst you have everything out of the refrigerator, take advantage of this time to throw away any products that are out of date or any leftovers that you are not going to use.
Fill a sink with warm soapy water, remove all trays, drawers and racks from the inside of the refrigerator and wash them in the sink. Don't forget to also wash the inside of the refrigerator along the sides and bottom, with the warm soapy water too.
Once the drawers and trays have been dried, they can be repositioned along with the contents of the fridge.
It is very important to clean up any spillages or food that has dropped onto the shelves, as they could come into contact with other foods and spoil or contaminate them. The same can be said about the frequent removal of food that is decaying or past its prime, which may pass on bad odours to perfectly fresh foods that are fine to eat.
Looking after your fresh food and your refrigerator will bring about many benefits. Correct refrigeration of perishable food and a refrigerator that is well looked after will mean that your food will be safer to eat, it will stay fresher for longer therefore saving you time and money and it will be healthier, as valuable nutrients are maintained within the product.