Food & Cooking · Unit 14
Preserving and Fermenting
Making food last, and letting microbes improve it
Every preservation method does one of two things: remove what microbes need, or add something they cannot tolerate. Once that framework is clear the techniques stop being a list.
The unit covers why food spoils, drying and salting, cold and freezing, canning and bottling, and fermentation - the method that improves food rather than merely holding it still.
This unit breaks down into 18 short steps and 110 questions, starting at difficulty 3 and building to 4. Below you can see exactly what it covers, how the path is structured, and worked examples with explanations.
- Steps
- 18
- Questions
- 110
- Difficulty
- 3-4
What this unit covers
- Fermentation
- Cold and Freezing
- Why Food Spoils
- Canning and Bottling
- Drying and Salting
Where this fits
Best after Food Science or alongside it.
Where people slip
Fermentation is spoilage steered in a useful direction. The same microbial activity that ruins milk makes yoghurt, and the difference is which organisms are encouraged.
How the unit is structured
Preserving and Fermenting runs as 18 short steps that unlock in order. 13 are practice rounds and 5 are challenge rounds that pull together everything before them. Questions start at difficulty 3 and climb to 4 as you progress.
Challenge rounds
Example questions
30 real questions from this unit, with the answer and the reason behind it, grouped by what they practise. There are 110 in the unit altogether.
Canning and Bottling
- Choose all that applyLevel 3
1. Which help preserve food in a jar? Pick all that apply.
- Plenty of sugarcorrect
- Vinegarcorrect
- An airtight sealcorrect
- Leaving the lid off
Sugar, vinegar, salt and a proper seal all help.
- Fill the blankLevel 3
2. Pickles are preserved because vinegar makes the food too ____ for most microbes.
- acidiccorrect
- sweet
- warm
- soft
Acid conditions prevent growth.
- Multiple choiceLevel 3
3. What is inside a sealed tin that stops food spoiling?
- Heated food sealed away from air and microbescorrect
- Preservative powder
- Ice
- Nothing at all
The food is heated and sealed so no microbes or air can get in.
- Put in orderLevel 3
4. Put these jam-making steps in order.
Answer: Cook the fruit with sugar -> Test whether it sets -> Pour into clean jars -> Seal while hot
Cook fruit with sugar, test the set, pot it, seal it.
- Sort into groupsLevel 3
5. Sort each method by the principle it uses.
Answer: Drying = Removing water; Salting = Removing water; Canning = Destroying microbes with heat; Pasteurising = Destroying microbes with heat
Preservation works by removing what microbes need or destroying them.
- True or falseLevel 3
6. Jam keeps well partly because it contains a lot of sugar.
Answer: True
True. High sugar makes water unavailable to microbes.
Cold and Freezing
- Choose all that applyLevel 3
7. Which foods freeze well? Pick all that apply.
- Breadcorrect
- Raw meatcorrect
- Cooked stewscorrect
- A whole fresh lettuce
Bread, meat and cooked meals all freeze successfully.
- Fact or fibLevel 3
8. Freezing food kills all the bacteria in it.
Answer: False
False. It stops them multiplying, but many survive and revive when thawed.
- Fill the blankLevel 3
9. Ice turning straight into vapour without melting is called ____.
- sublimationcorrect
- condensation
- melting
- boiling
Sublimation drives freeze drying and freezer burn.
- Multiple choiceLevel 3
10. Why does a fridge keep food fresh for longer?
- Cold slows microbes and chemical changescorrect
- Cold kills all microbes instantly
- Cold adds preservatives
- It does not
Cold slows the growth of microbes and the chemical changes that spoil food.
- Sort into groupsLevel 3
11. Sort each food by where it is best stored.
Answer: Milk = In the fridge; Fresh meat = In the fridge; Dried pasta = In the cupboard; Tinned beans = In the cupboard
Different foods need different storage.
- Put in orderLevel 4
12. Put these steps of validating a preserved product in order.
Answer: Design the formulation -> Model expected microbial behaviour -> Run a challenge test -> Conduct storage trials -> Set the shelf life
Design, model, challenge test, storage trial, set shelf life.
Drying and Salting
- Build the sentenceLevel 3
13. Build a sentence about preserving.
Answer: Drying removes the water microbes need
Drying removes the water microbes need.
- Choose all that applyLevel 3
14. Which are dried foods? Pick all that apply.
- Raisinscorrect
- Dried pastacorrect
- Dried herbscorrect
- Fresh milk
Raisins, dried pasta and dried herbs all have water removed.
- Multiple choiceLevel 3
15. How does salt help preserve meat?
- It pulls water out of the foodcorrect
- It adds water
- It cools the meat
- It kills nothing
It pulls water out, leaving conditions where microbes struggle to grow.
- Picture questionLevel 3
16. 🍇 What has been done to this fruit to help it keep?
- It has been driedcorrect
- It has been frozen
- It has been boiled
- It has been fried
Drying removes the water microbes would need.
- True or falseLevel 3
17. Salted fish and meat were important foods before refrigeration.
Answer: True
True. Salting let food be stored and carried for months.
- Fact or fibLevel 4
18. Combining several mild preservation methods can be as effective as one severe one.
Answer: True
True. This is the basis of hurdle technology.
Fermentation
- Build the sentenceLevel 3
19. Build a sentence about helpful microbes.
Answer: Helpful bacteria make acid that preserves food
Helpful bacteria make acid that preserves food.
- Choose all that applyLevel 3
20. Which foods are made by fermentation? Pick all that apply.
- Yoghurtcorrect
- Cheesecorrect
- Sourdough breadcorrect
- Boiled rice
Yoghurt, cheese and sourdough bread are all fermented.
- Fill the blankLevel 3
21. A defined mix of microbes added to control fermentation is a ____ culture.
- startercorrect
- finishing
- cleaning
- salt
Starter cultures standardise the process.
- Match the pairsLevel 3
22. Match each food to how it is preserved.
Answer: Raisin = Dried; Bacon = Salted or cured; Pickle = In vinegar; Frozen peas = Frozen
Different methods suit different foods.
- Multiple choiceLevel 3
23. What is yoghurt made by doing to milk?
- Adding helpful bacteria to thicken and sour itcorrect
- Freezing it
- Boiling it dry
- Adding flour
Helpful bacteria are added and they turn milk thick and tangy.
- Put in orderLevel 3
24. Put these sauerkraut steps in order.
Answer: Shred the cabbage -> Mix with salt -> Pack tightly into a jar -> Keep it under the brine -> Leave to ferment
Shred, salt, pack, submerge, ferment.
Why Food Spoils
- Build the sentenceLevel 3
25. Build a sentence about spoilage.
Answer: Microbes need water warmth and nutrients to grow
Microbes need water warmth and nutrients to grow.
- Choose all that applyLevel 3
26. Which are signs food has spoiled? Pick all that apply.
- A bad smellcorrect
- A slimy surfacecorrect
- Visible mouldcorrect
- A best-before date next week
Bad smell, slime and visible mould all indicate spoilage.
- Fact or fibLevel 3
27. If food looks and smells fine it is definitely safe to eat.
Answer: False
False. Many dangerous bacteria produce no visible or detectable change.
- Multiple choiceLevel 3
28. What makes food go mouldy?
- A fungus growing on the foodcorrect
- The food turning to stone
- Too much cold
- Nothing living
Mould is a fungus that grows on food when conditions suit it.
- Odd one outLevel 3
29. Which of these does NOT help food keep longer?
- Leaving it uncovered in a warm roomcorrect
- Refrigerating it
- Drying it
- Sealing it in a jar
Leaving food uncovered in a warm room speeds spoilage.
- True or falseLevel 3
30. You should not eat food that smells bad or looks mouldy.
Answer: True
True. Those are signs it is no longer safe or pleasant.
Where these questions come from. Each unit starts as a plan of the concepts it should cover and the difficulty it should span. Questions are written against that plan with AI assistance, then checked by a validator that rejects anything without a single defensible answer, an explanation, or plausible wrong options. How we write questions sets out the whole process, and corrections are fixed in the bank and reach the site and the app the same day.
How you practise
This unit mixes 12 different question formats, so you are recalling and applying rather than recognising the same layout every time.
- Build the sentence
- Choose all that apply
- Fact or fib
- Fill the blank
- Match the pairs
- Multiple choice
- Odd one out
- Picture question
- Put in order
- Sort into groups
- True or false
- Type the answer
Practise Preserving and Fermenting
110 questions across 18 steps. Start with step one and crawl at your own pace.
Play this unitRead about Preserving and Fermenting
Explainers from our blog on what this unit covers. Each one ends with real questions from the bank.
- How Does Pickling Preserve Food? Salt, Acid and the Microbes on Your SidePickling keeps food by making it too acidic for the microbes that spoil it, with vinegar or by letting bacteria make the acid. The two methods, and the science.September 15, 2026 · 5 min read
- What Is Fermentation in Food?How microbes preserve and transform ingredients, the main types, and why fermented foods taste the way they do.August 28, 2026 · 6 min read
More units in Food & Cooking
- What We EatFood groups, meals and where our food comes from
- Fruit and VegetablesGrowing, picking and eating plants
- In the KitchenTools, hygiene and staying safe while you cook
- From Farm to PlateThe journey food takes before it reaches you
- Grains and BreadThe crops that feed the world and the loaves they become
- Dairy and EggsMilk, cheese, butter and the remarkable egg
- Meat, Fish and ProteinProtein foods, how they cook and how they are caught or raised
- Herbs and SpicesFlavour, aroma and the trade that moved the world