Why does food go off, and what makes micro-organisms grow?
Food spoilage, the micro-organisms that cause it (bacteria, yeasts and moulds), the conditions micro-organisms need to grow, enzymic browning, and the signs that food has spoiled.
A focused CCEA GCSE Food and Nutrition answer on food spoilage, covering the micro-organisms responsible (bacteria, yeasts and moulds), the conditions they need to grow, enzymic browning, and the signs that food has gone off.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
CCEA wants you to know why food spoils, the micro-organisms that cause it (bacteria, yeasts and moulds), the conditions they need to grow, what enzymic browning is, and how to recognise that food has spoiled.
What food spoilage is
The micro-organisms
| Micro-organism | What it does |
|---|---|
| Bacteria | Multiply quickly; cause spoilage and food poisoning |
| Yeasts | Ferment sugars, producing alcohol and gas; spoil sweet foods |
| Moulds | Grow as visible fuzzy patches; spoil bread, cheese and fruit |
Conditions micro-organisms need
Removing any one of these conditions slows or stops growth, which is the basis of safe storage and preservation.
Enzymic browning
It can be slowed by coating the cut surface in lemon juice (acid) or water (to keep out oxygen), or by blanching to destroy the enzyme.
Signs of spoilage
Look for an off or sour smell, a change in colour, a slimy surface, visible mould, a bad taste, or food going soft or bubbling. These warn that food should not be eaten.
Linking to the rest of the course
Understanding spoilage explains food preservation (which removes the conditions micro-organisms need) and food safety (controlling bacteria to prevent food poisoning), and connects to date marks on labels.
Examples in context
- Example 1. Why the fridge keeps milk longer
- Cooling milk to below 5 degrees removes the warmth bacteria need to multiply quickly, so it stays fresh for days rather than hours. This applies the growth conditions to a familiar storage choice.
- Example 2. Salting and drying to stop spoilage
- Salted or dried foods such as cured ham or dried fruit keep for a long time because removing moisture stops micro-organisms growing. This links a growth condition (moisture) to traditional preservation.
- Example 3. Stopping apples browning on a fruit platter
- Brushing cut apple with lemon juice slows enzymic browning, because the acid and the coating reduce the reaction with oxygen. This shows a practical fix based on understanding the cause.
Try this
Q1. Name the three types of micro-organism that spoil food. [3 marks]
- Cue. Bacteria, yeasts and moulds.
Q2. State two conditions that micro-organisms need to grow. [2 marks]
- Cue. Warmth and moisture (also food and time, and often oxygen).
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA past-style6 marksDescribe the conditions that micro-organisms need to grow and explain how this knowledge helps us store food safely.Show worked answer →
Six marks: the conditions, then how storage uses them.
Micro-organisms such as bacteria need warmth, moisture, food (nutrients) and time to grow; many also need oxygen, and they grow best at a suitable pH (around neutral).
We store food to remove one or more of these conditions. Keeping food cold in the fridge (below 5 degrees) or frozen slows or stops growth by removing warmth. Drying or adding salt or sugar removes the moisture they need. Vacuum packing removes oxygen. Using food within its date and not leaving it out removes time and warmth.
Markers reward at least three correct conditions and clear links to safe storage.
CCEA past-style4 marksName the three types of micro-organism that spoil food and give one sign that food has spoiled.Show worked answer →
Four marks: three micro-organisms plus a sign.
The three types are bacteria, yeasts and moulds. Bacteria can cause both spoilage and food poisoning; yeasts ferment sugary foods; moulds grow as fuzzy patches on the surface.
Signs of spoilage include an off or sour smell, a change in colour, a slimy surface, visible mould, a bad taste, or the food going soft or bubbling. (Any one.)
Markers reward the three micro-organisms and one valid sign of spoilage.
Related dot points
- The principles of food preservation and the main methods, including freezing, chilling, canning, bottling, drying, salting, pickling and using sugar, and how each prevents micro-organisms from growing.
A focused CCEA GCSE Food and Nutrition answer on food preservation, covering the principles behind it and the main methods (freezing, chilling, canning, drying, salting, pickling and sugar) and how each stops micro-organisms growing.
- The principles of food safety and hygiene, including personal and kitchen hygiene, preventing cross-contamination, temperature control and the danger zone, food-poisoning bacteria, safe storage, and date marks.
A focused CCEA GCSE Food and Nutrition answer on food safety and hygiene, covering personal and kitchen hygiene, cross-contamination, temperature control and the danger zone, food-poisoning bacteria, safe storage and date marks.
- The reasons for cooking food, the methods of heat transfer (conduction, convection and radiation), the main cooking methods, and the effects of cooking on the appearance, texture and nutritional value of food.
A focused CCEA GCSE Food and Nutrition answer on cooking food, covering the reasons we cook, heat transfer by conduction, convection and radiation, the main cooking methods, and the effects of cooking on appearance, texture and nutrients.
- The functional and chemical properties of ingredients, including aeration, coagulation, gelatinisation, shortening, emulsification, denaturation, dextrinisation and caramelisation.
A focused CCEA GCSE Food and Nutrition answer on the functional and chemical properties of ingredients, covering aeration, coagulation, gelatinisation, shortening, emulsification, denaturation, dextrinisation and caramelisation, with examples in real dishes.
- Food labelling, including mandatory and voluntary information, nutrition information, traffic-light labelling, allergen information, and date marks, and how labels help consumers make informed choices.
A focused CCEA GCSE Food and Nutrition answer on food labelling, covering the mandatory and voluntary information on labels, nutrition panels, traffic-light labelling, allergen information and date marks, and how labels help consumers choose.