FN11: Food Spoilage & Microorganisms
Understanding how microorganisms cause food spoilage, the conditions they need to grow, and how to prevent spoilage in food storage and preparation.
Food Spoilage & Microorganisms
Understanding how microorganisms cause food spoilage, the conditions they need to grow, and how to prevent spoilage in food storage and preparation.
Key Fact: Food spoilage is caused by microorganisms (bacteria, yeasts, moulds) breaking down food.
Key Fact: Bacteria are the most common cause of food spoilage and food-borne illness.
Key Fact: Yeasts cause fermentation, producing alcohol and carbon dioxide — useful in bread-making but spoilage in other foods.
Key Fact: Moulds grow as visible fuzzy patches and can produce harmful mycotoxins.
Key Fact: The conditions microorganisms need to grow are summarised by FATTOM: Food, Acidity, Temperature, Time, Oxygen, Moisture.
Key Fact: The danger zone for bacterial growth is 5°C to 63°C; bacteria multiply fastest at around 37°C.
Key Fact: Signs of spoilage include: unpleasant smell, discolouration, slime, visible mould, gas bubbles, off-taste.
Key Fact: Enzymatic browning and oxidation are chemical changes (not microbial) that also spoil food appearance and quality.
Key Fact: Freezing at −18°C stops microbial growth but does not kill bacteria; they reactivate when thawed.
Key Fact: Pasteurisation heats food to 72°C for 15 seconds, killing most harmful bacteria without destroying flavour.
📋 Key Vocabulary and Concepts
For Food Spoilage & Microorganisms, you must know:
- Microorganism
- Bacteria
- Yeasts
- Moulds
- FATTOM
- Danger zone (5–63°C)
- Pasteurisation
- Mycotoxin
- Enzymatic browning
- Oxidation
- Pathogen
- Spore
❓ Practice Questions
Q: What does FATTOM stand for?
Q: What is the danger zone temperature range for bacterial growth?
Q: Name three signs of food spoilage.
Q: How does pasteurisation help prevent spoilage?
Q: Why does freezing at −18°C not kill bacteria?
Q: What is the difference between food spoilage and food poisoning?
Q: How do yeasts cause spoilage?
Q: What are mycotoxins and which microorganism produces them?
✅ Answers
- Food, Acidity, Temperature, Time, Oxygen, Moisture — the six conditions microorganisms need to grow.
- 5°C to 63°C. Bacteria multiply fastest at around 37°C (body temperature).
- Unpleasant smell, discolouration, slime, visible mould, gas bubbles, or off-taste (any three).
- It heats food to 72°C for 15 seconds, killing most harmful bacteria without significantly changing the food's flavour or nutritional value.
- Freezing stops bacterial growth by making water unavailable, but bacteria survive in a dormant state and can reactivate when the food is thawed.
- Spoilage makes food unpalatable (bad smell, taste, appearance) but may not always cause illness. Food poisoning is caused by consuming harmful bacteria or their toxins and causes illness.
- Yeasts ferment sugars, producing alcohol and carbon dioxide gas. This causes food to smell yeasty, taste sour, or develop gas bubbles.
- Mycotoxins are harmful chemical substances produced by moulds. They can cause illness even if the mould is removed.
🧭 Board Focus — AQA
Spec 8585. Written paper plus TWO NEAs: NEA1 Food investigation (a scientific food experiment report, ~15%) and NEA2 Food preparation task (a 3-hour practical, ~35%). AQA's NEA1 rewards the science — hypothesise, control variables, and link results to food science (gelatinisation, coagulation, denaturation).
Always check: specification details change — confirm paper structure and set texts against the current specification for your exam year.
🎯 Exam Tips
- Always refer to FATTOM when explaining how to prevent microbial growth — examiners look for this acronym.
- Distinguish clearly between spoilage (food becomes unpalatable) and food poisoning (food causes illness) — they are not the same.
- When asked about storage, always state the specific temperature: fridge at 0–5°C, freezer at −18°C or below.
- Use scientific vocabulary: say 'microorganisms' or 'pathogenic bacteria' rather than 'germs' or 'bugs'.
📝 Exam Technique
Food Preparation & Nutrition Exam Tips — Food Spoilage & Microorganisms:
1. For Food Spoilage & Microorganisms questions, show every step of your working clearly — method marks count even if the final answer is wrong
2. Check your answer makes sense in context (estimation, units, reasonableness)
3. Use correct mathematical notation and state formulae before substituting values
4. If a Food Spoilage & Microorganisms question asks you to 'prove' or 'show', write a logical chain of reasoning with a conclusion line
5. For problem-solving, identify the topic first, then recall the relevant method
1. For Food Spoilage & Microorganisms questions, show every step of your working clearly — method marks count even if the final answer is wrong
2. Check your answer makes sense in context (estimation, units, reasonableness)
3. Use correct mathematical notation and state formulae before substituting values
4. If a Food Spoilage & Microorganisms question asks you to 'prove' or 'show', write a logical chain of reasoning with a conclusion line
5. For problem-solving, identify the topic first, then recall the relevant method
⚠️ Common Errors
✗ Freezing kills all bacteria in food. ✓ Freezing stops bacterial growth but does not kill them; bacteria survive in a dormant state and can multiply again when thawed.
✗ All bacteria cause food spoilage. ✓ Many bacteria are harmless or even beneficial (e.g. in yoghurt production). Only some bacteria cause spoilage or food poisoning.
✗ If food looks and smells fine, it is safe to eat. ✓ Pathogenic bacteria may not produce any visible signs of spoilage — food can look and smell fine but still cause food poisoning.
✗ Mouldy food is safe to eat if you cut the mould off. ✓ Moulds can produce mycotoxins that spread through the food. Soft foods with mould should be discarded entirely.
✍️ Model Answer
Full-Mark Response
Explain the conditions that microorganisms need to grow and how understanding these conditions helps prevent food spoilage. (6 marks)
Microorganisms need six conditions to grow, remembered by the acronym FATTOM: Food (nutrients as an energy source), Acidity (most bacteria prefer pH 6.6–7.5; acidic conditions below pH 4.5 inhibit growth), Temperature (the danger zone of 5–63°C promotes rapid growth, with fastest reproduction at 37°C), Time (bacteria can double every 20 minutes in ideal conditions), Oxygen (aerobic bacteria need oxygen, though some are anaerobic), and Moisture (bacteria require water to survive and reproduce). Understanding these conditions allows us to control food safety: refrigeration below 5°C slows growth, cooking above 63°C kills most bacteria, reducing moisture through drying or adding sugar/salt prevents microbial activity, and acidic preservation (pickling in vinegar) creates an unfavourable pH. Limiting time in the danger zone — by cooling food quickly and not leaving it at room temperature for more than 90 minutes — is also critical. Each control targets one or more FATTOM conditions to prevent spoilage and food-borne illness.
📊 AO Deep Dive
Assessment Objective Analysis
AO1 (Knowledge & Understanding): Demonstrate knowledge and understanding of food spoilage & microorganisms, including nutritional principles, food science, and food safety regulations.
AO2 (Application): Apply knowledge and understanding of food spoilage & microorganisms to practical cooking contexts, recipe adaptation, and food choice decisions.
AO3 (Analysis & Evaluation): Analyse and evaluate food spoilage & microorganisms in relation to nutritional needs, food safety, sustainability, and cultural factors. Justify decisions with reasoned arguments and evidence.
📝 Exam Questions by Topic
- AQA Past Papers - Topic Questions -- AQA
- Edexcel Past Papers - Topic Questions -- Edexcel
- OCR Past Papers - Topic Questions -- OCR
- Eduqas Past Papers - Topic Questions -- Eduqas
🎬 Video Resources
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