1. The Law
2. Microbiological Hazards - Bacteria
10. Food Pests
Microbiological Hazards - Bacteria - learn
Bacteria are life forms that are invisible to the naked eye, but live on and in our bodies and food. There are thousands of different types of
A member of a large group of unicellular microorganisms lacking organelles and an organized nucleus, including some that can cause disease. and many of them are useful bacteria. A few are very harmful and can cause illness and encourage food to perish.
When food is contaminated it is impossible to see unless you look through a microscope. You can't see, taste or smell bacteria.
Types of bacteria
It is important to remember though, that not all types of bacteria are
causing or capable of causing harm. , most types of bacteria are beneficial to humans and we would find it difficult to live without them. For this course we are splitting bacteria into three groups; ‘helpful’ bacteria, ‘spoilage’ bacteria, and ‘pathogenic’ bacteria
Helpful Bacteria - Helpful bacteria allows us to grow crops, produce food including yoghurt, cheese and fizzy drinks. It allows us to digest the food we eat, create medical drugs, and even treat sewage to make safe.
Spoilage Bacteria – Spoilage bacteria makes food
Suffer complete ruin or decay. . A good example of this is the green mould you will see on bread that is a few days old.
Pathogenic Bacteria – Pathogenic bacteria is the name given to bacteria that can transmit illness such as food poisoning & food-borne disease.
Sources of Bacterial contamination
The state of being contaminated. occur? The simplest or least processed food can go through several stages before reaching the customer and there are some products that go through many stages before they are sold.
The contamination can go right back to the first process in the chain, such as growing, slaughtering, harvesting, processing, packing, delivering, storing, preparing, cooking, displaying, serving and selling.
Bacterial Contamination can occur when:
- Raw foods are contaminated by bacteria found in the natural environment.
- Pathogenic bacteria are transferred from raw food to high risk food at any stage of food handling.
- Cross contamination occurs, ie when bacteria is carried by the food handler’s hands, utensils or from raw food to high risk food.
Bacterial contamination occurs when raw food comes into contact with high risk food. If you touch raw food and then touch a high risk food without first washing your hands, you can easily spread bacteria. Also when liquid or juices from raw food comes into contact with high risk food.
Vehicles of contamination
Bacteria can only travel very small distances on their own, so they need something or someone to help them, anything that helps bacteria to travel is called a 'vehicle of contamination'.
People, animals, equipment, utensils are the most common vehicles of contamination.
Vehicles of contamination move pathogenic bacteria from a contaminated source, such as raw meat, to a place where the conditions are ideal for multiplication.
Preventing bacterial contamination
Bacterial contamination is responsible for most cases of food poisoning and food-borne disease. It takes just a small number of pathogenic bacteria such as Campylobacter or E.coli 0157 to cause a food-borne disease.
It is particularly important to ensure that:
- Raw and high risk foods are kept apart at all times
- This includes storage, transporting, preparation, display and point of sale
- All surfaces that come into contact with raw food are thoroughly cleaned and disinfected after use
One good way to help prevent
Indirect bacterial contamination (infection) of food, caused by contact with an infected raw food or non-food source. is to use colour coded preparation equipment, such as chopping boards and knives. Each colour is designated for a particular use; red for raw red meat, green for vegetables. This is a good idea as it helps remind food handlers to prepare raw and high risk foods using separate equipment.
What do bacteria need to multiply?
When food poisoning bacteria spend enough time on the right types of food at ambient, (room), temperatures, they can quickly multiply to dangerous levels.
The four main requirements bacteria need to multiply are 1 Food 2 Moisture 3 Warmth and 4 Time.
1. Food - 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.
Examples are meat, poultry, eggs, shellfish, milk and dairy products, cooked rice, pasta and any product made from the foods listed. All these foods are subject to bacterial growth even after they have been cooked and served cold later. Such ready to eat items are classified as High-Risk Foods.
2. Moisture - Food poisoning bacteria must have moisture to stay alive. Bacteria will not multiply in dried foods, but as soon as liquid is added to food like powdered milk, dried eggs, pasta, rice, then the products will provide ideal conditions for bacteria to multiply. However if enough sugar or salt have been added to foods such as bacon, biscuits, jam and confectionery, this will absorb the available moisture in the food so the bacteria cannot multiply as easily.
Example. 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.
3. Warmth - Most food poisoning bacteria multiply at temperatures between 5°C and 63°C, known as the ‘Danger Zone’.
A comfortable ambient temperature, generally taken as between 20-25°C. is usually within the Danger Zone.
The ideal temperature for bacteria to multiply is 37°C, this is the average human body temperature. When food 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 and resume multiplication when conditions are more suitable, ie back in the Danger Zone.
Freezing will make bacteria dormant and kill many; however, it does not kill them all. When frozen food is thawed it comes back into the Danger Zone and bacterial multiplication starts again.
4. Time - When food poisoning bacteria are left in warm conditions, (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. In a process known as ‘Binary Fission’, 1000 bacteria within 1 hour & 40 minutes will multiply to over 1 million bacteria!
If you stop or remove one of the 4 requirements (Food, Moisture, Warmth or Time) you will stop the growth of bacteria.
Bacteria and the Danger Zone
Cooking at high temperatures kills most bacteria, provided that the food is cooked for long enough.
You must cook food for at least two minutes at 75°C right through to the centre or the thickest part of the food.
Some types of bacteria can survive even higher cooking temperatures and other harsh conditions like dehydration or disinfection. The reason why is that they form spores, a protective coating or shell to protect themselves.
Bacteria do not multiply when they are in spore form, but as soon as conditions improve, back into the Danger Zone, the bacteria emerge from their spores and will resume multiplication.
Food is likely to be in the Danger Zone if:
- It is kept at room temperature
- Heated slowly or cooled slowly
- Left in the sun, such as in a shop window
- A hot sauce is poured onto cold food
The key to safe food is to ensure that the time taken from preparation, cooking through to 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.
Always remember the Danger Zone
is 5°C to 63°C.
High risk foods
High risk foods are usually high in protein & moisture. They must be stored separately in either fridge or freezer, and are most commonly associated with food poisoning outbreaks.
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.
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
- Baby Foods, (once opened).
Remember that chilled & frozen storage slows down bacterial multiplication, and time from preparation through 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, pasta, rice, flour, crisps, canned foods. However, you need to be aware that once they are brought back into the Danger Zone, they can attract moisture and bacterial multiplication starts again.
You may also cook a dry food such as rice, pasta, gravy, custard powder. Once you have added water, (moisture), bacterial multiplication can resume.
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