1. The Law
Bacteria - learn
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 can cause food poisoning.
In this course we will talk about the 3 main types of Bacteria.
Types of bacteria
Helpful Bacteria Spoilage Bacteria Pathogenic 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 just destroy 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 & Food-Borne Disease.
Pathogenic Bacteria are invisible to the naked eye.
You also 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.
This can happen when:
- If you touch raw food and then touch a high risk food without first washing your hands.
- Or when liquid or juices from raw food comes into contact with high risk foods. (defrosting turkey above a cooked quiche)
- Or you do not clean a work area between handling raw & 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:
FOOD – MOISTURE – WARMTH – TIME
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. But as soon as water/liquid is added, 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 then 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 and room temperature is usually within the Danger Zone.
Food that is kept at temperatures colder than 5°C or hotter than 63°C, bacterial growth slows down or stops.
However, most bacteria can survive cold temperatures, (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!
Very Important Point: 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
- Prepare the food ideally 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)
Always remember do not keep food in the Danger Zone any longer than necessary
Keep hot food really hot and cold food really cold
High & Low Risk Foods
These are foods that are normally high in protein & 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 can not cook them, you can not 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 a 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 & pasta
Remember that chilled & frozen storage slows down bacterial multiplication and 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 can resume.
THE DANGER ZONE Always remember the Danger Zone: 5°C to 63°C
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