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How does Contamination Occur?

Before we start to explain how to control food safety, we need to understand how food becomes contaminated.
© International Culinary Studio

Before we start to explain how to control food safety, we need to explain how food becomes contaminated, as this is one of the key control methods of hazards.

Food becomes contaminated through a variety of ways, mainly through people, and this causes food bourne illnesses. Poor food hygiene leads to pathogens entering the food.

Contamination happens due to:

  • Poor or insufficient handwashing
  • Cross-contamination
  • Incorrect storage and cooking temperatures
  • Contamination of food by animal waste
  • Contamination by other means

Poor or insufficient handwashing

  • Pathogens are introduced to food by a human that is infected and then handles the food before washing their hands thoroughly and correctly.
  • These pathogens are transferred to the food from trace amounts of bacteria, virus or feacal matter that is present on their hands.

Please refer to our course on Personal Hygiene to find out more on the correct way to wash your hands.


  • Food, kitchen equipment and surfaces can become contaminated by raw food products such as meat and poultry or by touching them.
  • Microbes are transferred from one piece of food to another by using the same knife, cutting board or other utensil without proper handwashing, washing and sanitizing the surface or utensil in between uses.
  • Food that is fully cooked becomes re-contaminated when it touches other raw foods or drippings from raw foods that contain pathogens. For example if cooked food is placed onto a board that has been used to prepare raw food.

Incorrect storage and cooking temperatures

  • Pathogens usually need time to multiply to a larger number in the food before there are sufficient to make someone sick or cause disease.
  • Pathogens can multiply rapidly in food that is kept at incorrect temperatures. For example pathogens will multiply faster if a cooked dish of food is left out of the refrigerator. Food should be stored or held at the correct temperatures for example cold below 4°C / 39°F and hot food above 65°C/149°F.
  • Generally, refrigeration or freezing prevents most bacteria from growing.
  • Most parasites, viruses and most bacteria are killed when food is kept hot or maintained at the correct hot temperature.

Contamination of food by animal waste

  • Many foodborne microbes are present in healthy animals raised for consumption and so they are present in the meat when it is delivered.
  • Meat and poultry may become contaminated whilst being slaughtered when they come into contact with intestinal contents.

Contamination by other means

  • Food can become contaminated by chemicals used in the kitchen; cleaning and pest chemicals for example.
  • Foreign objects can enter the food.
  • Fresh fruits and vegetables can become contaminated if they are washed with water that is contaminated with animal manure or human faeces
  • Fruit and vegetables can also have residual poisonous chemicals if they are not washed correctly before use.

This interesting infographic from The Centre for Disease Control research shows how salmonella poisoning occurred and how these outbreaks could have been prevented through the control of hazards.

To download this Infographic or read more about the prevention, please go to the Centre for Disease Control here


Take some water-based paint and paint it onto your hand, palm and fingertips (make sure it is washable paint). Once you have done this, take a large piece of paper and touch your hand down as many times as you can onto the paper before you see no more paint.

How many times did you see the transfer of paint? This is a very good example of how bacteria and viruses are transferred when a person does not wash their hands correctly with soap and water. Each time they touch something more bacteria are transferred.

Hands and equipment such as knives, chopping boards and benches are no different, they keep on contaminating food until they are washed and sanitised!

© International Culinary Studio
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Introduction to HACCP for Food Safety

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