Food safety
Microbes and spoilage, food preservation methods and food additives.
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Before you begin
Food goes off when microbes grow in it. This topic explains how microbes spoil food, how preservation methods slow them down, and what food additives are used for.
Be comfortable with: the idea that living things need water, food and suitable conditions to grow.
Learning goals
- Microbes
- Microbial action on food
- Reducing microbial activity
- Lowering pH
- Reducing oxygen
- Reducing water
- Using high temperature
- Using low temperature
- Preservatives
- Nutritional supplements
- Texture and appearance modifiers
Syllabus statements covered
- state what microbes are
- describe the action of microbes on food (e.g. bacteria on milk, mould on bread)
- state that stopping or reducing microbial activity may prevent food spoilage
- describe the following methods of preventing food spoilage and give example(s) for each of them: — lowering pH (pickling)
- describe the following methods of preventing food spoilage and give example(s) for each of them: — reducing oxygen supply (bottling and vacuum packaging)
- describe the following methods of preventing food spoilage and give example(s) for each of them: — reducing water content (freeze-drying, dehydration and use of chemical preservatives)
- describe the following methods of preventing food spoilage and give example(s) for each of them: — using high temperature (sterilisation, pasteurisation and canning)
- describe the following methods of preventing food spoilage and give example(s) for each of them: — using low temperature (freezing)
- explain the use of the following food additives and give examples for each of them: — preservatives (e.g. salt, sugar, sulfur dioxide, vinegar)
- explain the use of the following food additives and give examples for each of them: — nutritional supplements (e.g. minerals, vitamins)
- explain the use of the following food additives and give examples for each of them: — texture and appearance modifiers (e.g. food colourings, starch)
Lessons
Work through them in order.
- Microbes and food spoilageExplain changes caused by bacteria in milk and mould on bread, useful roles of microbes, and the limits of visible safety evidence.
- Food preservation methodsCompare how pH, oxygen, available water and temperature affect microbes, and explain the limits of each preservation method.
- Food additives and their purposesClassify uses of additives as preservatives, nutritional supplements or modifiers, using their stated purposes.
Practise and check
Or choose
Topic reference
Quick reference
| Method | How it slows microbes |
|---|---|
| pickling | more acidic |
| vacuum packing | less oxygen |
| drying | less water |
| pasteurisation | heat reduces microbes |
| freezing | low temperature |
| Additive group | Purpose |
|---|---|
| preservatives | delay spoilage |
| nutritional supplements | add nutrients |
| modifiers | change appearance or texture |
Core knowledge to remember
- Microbes are too small to see without a microscope; a visible mould patch is a large colony.
- Not all microbes are harmful: some are used to make bread and yoghurt.
- Cooling slows microbes but does not kill them all.
- Food can look normal and still be unsafe.
Common mistakes
- Saying all microbes are harmful.
- Saying freezing or refrigeration kills all microbes.
- Saying every additive is a preservative.
- Testing whether food is safe by tasting or smelling it.