Preserving
Food
Revise and Test
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Scientific Principles
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Food preservation stops food going bad.
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1. Complete the names of the main microorganisms responsible for the
contamination of food. b……., / y….., /
m….. .
Preservation changes the environment
that the food is in and therefore prevents
the growth of micro-organisms.
2. What conditions do micro-organisms
need to multiply and grow?
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3. What substances occur naturally in
food which also cause deterioration? *
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Reasons for
Preservation
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Throughout history people have
found ways to preserve food like
smoking or sun-drying this fish.
Ideally we would eat food fresh.
This is not possible as we need food
to last over a period of time and not
just when immediately available.
4. Give one reason for preserving
food. *
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Preservation Methods
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To preserve food like this fruit we need
to remove the conditions microorganisms need to survive and grow.
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5. How does each of these methods help
preserve food?
(a.) the use of high temperatures
(b.) the use of low temperatures
(c.) dehydration
(d.) adding chemicals
(e.) sealing / vacuum packing
(f.) irradiation using new technology. *
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The Use of Heat
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Nearly all bacteria, yeasts, moulds
and enzymes are destroyed by
heating to 100ºc.
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6. How does canning and bottling
preserve food?
7. What temperature is milk heated to
during pasteurisation which kills most
harmful bacteria? (a.) 20ºc, (b.) 59ºc,
(c.) 72ºc, (d.) 105ºc.
8. What two foods or drinks are
commonly preserved by ultra heat
treatment (UHT)? *
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The Use of Low Temperature
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Low temperatures remove warmth and
moisture that micro-organisms need for
growth.
Food can be frozen or chilled.
9. What effect does freezing have on
micro-organisms?
10. How does freezing remove the
moisture that micro-organisms need for
growth?
11. What effect does chilling have on
micro-organisms? *
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Drying
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Drying or dehydration removes the
moisture micro-organisms need for
growth and reproduction.
This is a very old method of
preservation where fruit, vegetables,
fish and meat can all be preserved by
drying.
12. Name one traditional method of
drying that has been used for
centuries.
13. Name one newer mechanical
method of drying that is used
commercially. *
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Chemical Methods
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Traditional methods of preserving food by
chemical methods include vinegar, salt, sugar,
alcohol and wood smoke.
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14. How do most chemical
preservatives work?
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15. Name one other more recent
chemical preservative. *
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Removal of Air
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Canning and bottling use air removal
to preserve as well as sterilise.
Removal of air is also used in vacuum
packing and modified atmosphere
packing.
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16. What is vacuum packing?
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17.What gases are removed in
modified atmosphere packing?
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18. Give two examples of foods that
are preserved by these methods. *
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Irradiation
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Irradiation is the process of
passing X rays from radioactive or
electron beams through food.
The energy similar to ultraviolet
light does not make the food
radioactive but irradiated food must
be clearly labelled.
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19. Give two uses of irradiation.
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20. Give two examples of foods that
are most suitable for irradiation. *
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Strawberries
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There are several ways to
preserve any one kind of food.
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Some methods will retain the
qualities of the fresh strawberry
in flavour, texture, colour,
appearance and nutritional value
while others will not.
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21. Give three different ways
that these strawberries could
have been preserved. *
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Effects on Food
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The characteristics and nutritional
value of food like this can be
changed by preservation.
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22. How would the character and
nutritional content of fruit be
changed by jamming?
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23. What methods of preservation
are most likely to change the taste
of food? *
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Suggested Answers
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1. Bacteria, yeasts and moulds.
2. Warmth, moisture, food and time to grow.
3. Enzymes.
4. Food safety, to eat at a later time, a glut of food in season/cheaper.
5. (a.) kills micro-organisms, (b.) makes them inactive, (c.) removes water, (d.)
to change acid/alkaline/moisture content, (e.) removes air (f.) kills microorganisms.
6. By heating to kill micro-organisms and then sealing to exclude air.
7. (c.) 72ºc.
8. Milk and fruit juices.
9. Stops growth of micro-organisms and slows down enzyme activity.
10. Turns water to ice crystals so water is no longer available.
11. Slows down growth of micro-organisms compared with room temperature.
12. Sun dried, oven dried.
13. Spray drying, hot air beds, freeze drying.
14. They reduce the moisture content of food by osmosis.
15. Antioxidants, sulphur dioxide, nitrates. *
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Suggested Answers continued
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16. The food is sealed in plastic and all the air is removed.
17. Carbon dioxide and nitrogen.
18. Bacon, cold meats, cheese, sausages, fish etc.
19. Stops vegetables from sprouting, destroys parasites and insects, delays
ripening, allows longer storage.
20. Bananas, mangoes, shellfish, strawberries, potatoes, spices, pulses.
21. Jamming, freezing, bottling, chilling, drying, irradiation, canning, in alcohol,
fruit juice, in jelly.
22. Preservation may alter the characteristics or qualities like texture or colour.
The nutritional value may change with lost vitamins but food energy is added
with the sugar content.
23. Pickling, drying, smoking, salting, adding sugar in jam, canning. *
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