1. © ORCA Education Limited 2005
Preserving Food
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© ORCA Education Limited 2005

2. Scientific PrinciplesA
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Food preservation stops food going bad.
1. Complete the names of the main micro-organisms 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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SAY Micro-organisms are usually associated with food spoilage but they can also be beneficial and are used safely in the manufacture of many different foods such as yogurt, cheese, wine, bread and Quorn. Lactic acid bacteria cultures are used to make cheese and yogurt as these are not harmful. Moulds are injected into cheese to produce blue-veined cheeses like Danish Blue and Stilton. Yeast of course, is essential in the manufacture of bread and alcoholic drinks. Quorn is made by using micro-organisms in a fermentation process similar to making yogurt or beer.^PAUSE=1300^
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3. What substances occur naturally in food which also cause deterioration? *

3. 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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4. Preservation Methods A
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To preserve food like this fruit we need to remove the conditions micro-organisms need to survive and grow.
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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5. The Use of Heat A
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Nearly all bacteria, yeasts, moulds and enzymes are destroyed by heating to 100ºc.
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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SAY Heat is a very popular way to preserve food and canning is one of the most widely used. Food can be kept for several years but once opened must be treated as fresh food. However, the process does alter the characteristics of the food. Tinned peas are quite different to fresh. Heat treatment by pasteurisation extends shelf life and makes the food safer to eat and is used for milk, cream, orange juice and beer. ^PAUSE=1300^
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6. 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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SAY Frozen food is sometimes more nutritious than fresh food as it is often frozen within hours of being harvested. However, some foods need to be frozen very quickly as slow freezing will produce large ice crystals that will break down the walls of cells in the food and you will end up with a mushy mess. Manufactures use several kinds of methods to freeze food quickly such as blast freezing or immersion freezing so that your frozen raspberries are perfect when defrosted! ^PAUSE=1300^
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7. Drying A
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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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SAY When you have a cup of instant coffee, you may well be drinking a product that has been through the process of accelerated freeze drying. This method of drying food is very good as there is little damage to the food product and reconstitution is also usually good. It is also used for mashed potato and many instant meals. Many different foods can be dried including milk, fish, meat, vegetables, pulses, soups and herbs. Flavour and texture is sometimes changed dramatically, for instance, grapes are dried to become raisons and sultanas. Dried food is often a concentrated source of nutrients although fruits and vegetables lose their vitamin C ^PAUSE=1300^
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8. Chemical Methods A
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Traditional methods of preserving food by chemical methods include vinegar, salt, sugar, alcohol and wood smoke.
14. How do most chemical preservatives work?
15. Name one other more recent chemical preservative. *
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9. Removal of Air A
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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.
16. What is vacuum packing?
17.What gases are removed in modified atmosphere packing?
18. Give two examples of foods that are preserved by these methods. *
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SAY Crisps and salad vegetables are examples of modified atmosphere packaging. Vacuum packing and modified atmospheric packing extends the shelf life of food as it delays the growth of micro-organisms. They are packed in sealed plastic film and must be stored in a cool place. Some foods like bacon also have chemical preservatives such as sodium nitrite added to them so they can keep longer. The food looks, smells and tastes just like fresh food.^PAUSE=1300^
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10. Irradiation A
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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.
19. Give two uses of irradiation.
20. Give two examples of foods that are most suitable for irradiation. *
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11. Strawberries A
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There are several ways to preserve any one kind of food.
Some methods will retain the qualities of the fresh strawberry in flavour, texture, colour, appearance and nutritional value while others will not.
21. Give three different ways that these strawberries could have been preserved. *
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12. Effects on Food A
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The characteristics and nutritional value of food like this can be changed by preservation.
22. How would the character and nutritional content of fruit be changed by jamming?
23. What methods of preservation are most likely to change the taste of food? *
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13. Suggested Answers 1. Bacteria, yeasts and moulds.
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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 micro-organisms.
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. *

14. Suggested Answers continued
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Suggested Answers continued
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. *