Food can be ruined by bacteria, enzymes, moulds and yeasts. Some will spoil food by making it unappetising, whilst others can cause diseases and food poisoning.


10 main causes of food poisoning...

Cause: Prevention:
Preparing food too far in advance. Prepare food as close to consumption as possible.
Food cooled too slowly before being refrigerated. Food must be refrigerated within one and a half hours.
Food not reheated enough to kill bacteria. Reheat food until it is piping hot all the way through.
Contaminated food eaten. Do not consume food after its eat-by date, and store correctly.
Food undercooked. Cook food thoroughly - use a temperature probe.
Poultry not thawed properly. Make sure no ice crystals remain.
Cooked food cross-contaminated by raw food. Use separate equipment for raw and cooked food.
Hot food kept warm at less than 63 degrees Celsius. Check food with a temperature probe.
Food handlers passing on infection. Remove jewellery, wear aprons, wash hands, report illnesses, etc.
Left-overs reheated. Use quickly, store below 5 degrees Celsius, reheat thoroughly.

Many of the changes in food are caused by micro-organisms and enzymes and you will need to know about their characteristics.


There are 3 types of micro-organisms...

1. Moulds:

Reproduce by spores, which travel in the air. Can produce mycotoxins, which can be poisonous. Bread, jam and cheese may become mouldy.

2. Yeasts:

Break down sugars in food to produce carbon dioxide and alcohol. Useful in wine and beer production.

3. Bacteria:

Most bacteria are not dangerous. Pathogenic bacteria are bacteria that can cause illness in humans. Bacteria are not visible to the naked eye.

This table shows the most common types of food poisoning bacteria:

Bacteria: Incubation: Symptoms: Found in: Important points:
Bacillus cereus 1-6 hours Nausea, vomiting, diarrhoea. Cooked rice, especially if kept warm. Cool pasta and rice quickly.
Camploybacter 2-10 days Diarrhoea, abdominal pain. Meat, shellfish, milk, untreated water. Most commonly reported cause of food poisoning.
Clostridium botulinum 12-48 hours Paralysis. Can be fatal. Canned food especially fish, meat and vegetables. Water and soil. Rare form of poisoning. Bacteria produce spores, which survive high temperatures.
Clostridium perfringens 10-24 hours Diarrhoea, abdominal pain. Raw meat, cooked meat and products. Soil. Very common cause of poisoning. Most active at 45-50 degrees Celsius.
Escherichia coli (E-Coli) 1-2 days Diarrhoea with blood, vomiting. Raw meat, untreated milk and dairy products. Drink bottled water when abroad.
Listeria monocytogenes Up to 70 days Flu symptoms, blood poisoning, meningitis. Soft cheeses made with unpasteurised milk, pate, cook/chill foods. Dangerous to pregnant women.
Salmonella 12-48 hours Diarrhoea, fever, vomiting, abdominal pain. Meat, raw eggs, cream, seafood. Babies, the elderly and pregnant women should not eat raw eggs. Poultry must be defrosted well before cooking.
Staphyloccus aureus 1-8 hours Vomiting, diarrhoea. Meat and meat products, eggs. Nose, throat and cuts of food handlers. Personal hygiene is very important.

Micro-organisms are usually only visible under a microscope. They are found in water, soil, air and rubbish and on animals, humans and equipment. They can be transferred to food by poor hygienic practices - for example, by humans, flies and rodents. Some foods may already contain micro-organisms - for example, salmonella in chicken.


Enzymes can cause undesirable changes in foods that make them unsightly. This is called browning and is caused by the action of an enzyme called polyphenol oxide in the presence of oxygen. Enzymatic browning can be reduced by:

1. High temperatures: For example, blanching cut vegetables in boiling water.

2. Acidic conditions: For example, dipping cut fruit into lemon juice.

3. Other methods: These are used in commercial food processing.

    [*]Diarrhoea. [*]Vomiting. [*]Abdominal pain can be very unpleasant and can even cause hospitalisation, or death, for vulnerable groups such as...
      - babies. - young children. - the elderly. - people whose immune systems are damaged.

This was introduced to try to reduce the number of food poisoning cases in the UK. Its regulations cover food production from the original food grower or producer right through to the people who manufacture, serve or sell it. If its regulations were not met, the following could be imposed:

  • Fines
  • Imprisonment
  • Closure of premises
  • Compensation to consumers

In 1995, the Food Safety (Temperature Control) Regulations were introduced, which specified the specific temperatures at which food (such as chilled goods) should be stored.

Both of these Acts are enforced by Environmental Health Officers (EHOs) who are employed by Local Authorities and who can inspect premises without giving prior notice.