What are microorganisms and enzymes, and how do they cause food to spoil or be useful?
Microorganisms (bacteria, yeasts and moulds) and enzymes: the conditions they need to grow, how they spoil food, and how some are used helpfully in food production.
A focused answer on microorganisms and enzymes for OCR GCSE Food Preparation and Nutrition (J309), covering bacteria, yeasts and moulds, the conditions they need to grow, how enzymes and microorganisms spoil food, and the helpful uses of microorganisms.
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What this dot point is asking
OCR wants you to know the microorganisms found in food (bacteria, yeasts and moulds), the conditions they need to grow, how they and enzymes spoil food, and how some microorganisms are used helpfully. This is the foundation for the rest of the food safety content.
The three types of microorganism
- Bacteria are the main cause of food poisoning and much spoilage. In good conditions a single bacterium can divide about every minutes, so numbers rise very fast.
- Yeasts ferment sugars, producing carbon dioxide and alcohol. They spoil sugary and acidic foods (fruit juice, jam) but are also used helpfully in bread and brewing.
- Moulds grow as visible fuzzy patches on the surface of food (bread, cheese, fruit) and spread by spores in the air. Some moulds produce toxins, so mouldy food should usually be thrown away.
The conditions microorganisms need
This is why we chill food (remove warmth), dry or preserve it (remove moisture), and do not leave it out for long (reduce time). Some bacteria need oxygen (aerobic) and some grow without it (anaerobic), which matters for vacuum-packed and canned foods.
How enzymes spoil food
Enzyme action can be slowed by chilling (cold slows enzymes) and stopped by blanching (brief heating destroys the enzyme), which is why vegetables are blanched before freezing so they do not deteriorate in the freezer.
Helpful uses of microorganisms
Not all microorganisms are harmful. Yeast ferments bread dough (producing carbon dioxide to make it rise) and is used in brewing. Bacteria are used to make yoghurt (Lactobacillus turns lactose into lactic acid, souring and thickening the milk) and cheese. Mould ripens blue cheeses such as Stilton and the rinds of brie and camembert. These useful microorganisms are encouraged under controlled conditions.
Try this
Q1. State the temperature range of the danger zone. [1 mark]
- Cue. 5 to 63 degrees C.
Q2. Name one microorganism used helpfully in food production and what it does. [2 marks]
- Cue. Yeast raises bread (carbon dioxide), or bacteria make yoghurt (lactic acid), or mould ripens blue cheese.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20186 marksExplain the conditions that bacteria need to grow, and describe how a cook can use this knowledge to keep food safe.Show worked answer →
A 6-mark free-response question linking the conditions to control measures.
Bacteria need warmth, moisture, food and time to grow (some also need or avoid oxygen). They multiply fastest in the danger zone, between 5 and 63 degrees C, and ideally around body temperature (37 degrees C); in good conditions one bacterium can divide about every 20 minutes.
A cook uses this to keep food safe: keep high-risk food out of the danger zone by storing it in the fridge below 5 degrees C or holding hot food above 63 degrees C; remove the warmth (cooling and chilling quickly); reduce the time food spends at room temperature; remove moisture (drying); and cook food thoroughly so the centre reaches above 75 degrees C to destroy bacteria.
Top-band answers (5 to 6 marks) state the four conditions, name the danger zone and give several control measures linked to removing a condition.
OCR 20204 marksDescribe two ways that microorganisms are used helpfully in food production.Show worked answer →
A 4-mark structured question.
Any two helpful uses: yeast is used to ferment bread dough, producing carbon dioxide that makes the dough rise, and to ferment sugars into alcohol; bacteria are used to make yoghurt (Lactobacillus turns the lactose in milk into lactic acid, thickening and souring it) and cheese; mould is used to ripen blue cheeses such as Stilton and the rind of brie and camembert.
Markers reward two correct examples with the microorganism and what it does, for example yeast raising bread and bacteria making yoghurt.
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