In this chapter
This chapter introduces you to the concept of bacteria, highlighting the four essential factors for bacterial growth, and the concept of high and low risk foods.
There are thousands of different types of bacteria and many of them are useful bacteria. We need many of them to live.
A few are very harmful and some can cause food poisoning.
In this course we will talk about the 3 main types of Bacteria.
Types of bacteria
Helpful Bacteria - Allows us to:
- Digest the food we eat
- Produce food including yoghurt, cheese and fizzy drinks
Spoilage Bacteria - A good example of this is the green mould you will see on bread that is a few days old. Never destroy just the slice with mould and use the rest. You must destroy the whole loaf.
Pathogenic Bacteria - This is the name for bacteria that can transmit illness such as, Food Poisoning and Foodborne Disease.
Pathogenic Bacteria are invisible to the naked eye.
You cannot see, taste or smell them which make them particularly difficult to control.
How Does Bacterial Contamination Happen?
Cross-contamination is a major cause of bacterial contamination.
This is when pathogenic bacteria are transferred from raw foods to cooked foods.
It can happen:
- If you touch raw food and then touch a high-risk food without first washing your hands.
- When liquid or juices from raw food comes into contact with high-risk foods, (defrosting a turkey above a cooked quiche).
- You do not clean a work area between handling raw and cooked foods.
One good way to help prevent cross-contamination is to use colour-coded preparation equipment, such as chopping boards and knives.
Bacteria need help to move to another food, anything that helps bacteria to travel is called a 'vehicle of contamination'.
People, animals, equipment, utensils are the most common vehicles of contamination.
What do Bacteria Need to Multiply?
These are the four main requirements bacteria need to multiply:
Bacteria are like all living things, they need nutrients (food) to survive.
Different types of food poisoning bacteria can live on a range of foods but most prefer food that is moist and high in protein.
For example: Meat, poultry, eggs, shellfish, milk and dairy products, cooked rice, pasta and any product made from the foods listed.
Food poisoning bacteria must have moisture to stay alive.
Bacteria will not multiply in dried foods such as dried pasta, rice, biscuits. As soon as water/liquid is added however, bacterial multiplication starts again.
A good example of this is a pack of biscuits.
When you open the packet, the biscuits will be very dry. However, just watch what happens to the biscuits if you leave them opened for a few days. They will go “soggy” as they take moisture from the air. Once this happens, bacterial multiplication starts again.
Most food poisoning bacteria multiply at temperatures between 5°C and 63°C.
This range of temperatures is called the Danger Zone. Room temperature is usually within the Danger Zone.
Bacterial growth slows down or stops in food that is kept at temperatures colder than 5°C or hotter than 63°C.
Most bacteria can survive cold temperatures though, (in a fridge or freezer), and resume multiplication when they are back in the Danger Zone.
When food poisoning bacteria are left in the Danger Zone, on the right type of food with adequate moisture, they will reproduce quickly.
Time is a critical point in preventing the multiplication of bacteria
Most types of food poisoning bacteria take around 10 to 20 minutes to multiply
This is called Binary Fission
100,000 bacteria within 2 hours will multiply to over 6.4 million bacteria!
Key Point 1
If you stop or remove one of the 4 requirements you will stop the growth of bacteria.
Bacteria and the Danger Zone
The key to safe food is to ensure that the time taken from preparation - cooking - serving is kept to a minimum
- Ideally prepare the food within 30 minutes (if not, put it back in the fridge)
- Cook the food for 2 minutes at 75°C (to the centre or thickest part)
- Serve the food within 20 minutes (or hot-hold at above 63°C)
Key Point 2
Do not keep food in the Danger Zone any longer than necessary
Keep hot food really hot and cold food really cold
These are foods that are normally high in protein and moisture and can easily allow bacterial multiplication.
Many high-risk foods are “ready to eat” and as a result they may not be cooked before serving. If you cannot cook them, you cannot destroy any bacteria that may be present.
As a result, you must only leave these food types in the Danger Zone for the shortest amount of time possible and only take out of the fridge or freezer when you are going to use them.
Examples of High Risk Foods are:
- Cooked meat & poultry
- Pates, savoury spreads, gravy, stews, meat pies, stock
- Milk, cream, custards, cakes with cream, ice cream, dairy products
- Soft Cheese
- Egg based products, mayonnaise, mousse, quiches
- Shellfish, mussels, oysters
- Cooked rice and pasta
Remember that chilled and frozen storage slows down bacterial multiplication and the time from preparation to service is critical.
Low Risk Foods
By removing moisture, (with sugar or salt), or by using a vinegar, (pickle), you are effectively taking away one of the four main elements that bacteria need to survive.
It is rare for these foods to be associated with food poisoning outbreaks.
Examples of Low Risk Foods are:
- Jam, biscuits, dried foods, cereal, dried pasta, dried rice, flour, crisps, canned foods.
Please remember: Once you have added water, (moisture), bacterial multiplication will resume.
Key Point 3
The DANGER ZONE - always remember the Danger Zone is 5°C to 63°C
By the end of this chapter you should have developed the following understanding and insights:
- An awareness of the terms helpful, spoilage and pathogenic bacteria
- An awareness of the fact that you cannot see, taste or smell the presence of bacteria
- An understanding of the main requirements bacteria need to multiply
- An awareness of the terms high risk and low risk foods