1. © ORCA Education Limited 2005
Preparing Food
Revise and Test
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© ORCA Education Limited 2005

2. Reasons to Cook Food A There are many reasons why we cook food.
Answers
There are many reasons why we cook food.
It makes food easier to eat, reduces bulk so more can be eaten and makes food easier to digest.
1. How does cooking make food more appetising?
2. How does cooking make food safe to eat? *
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3. The Transfer of Heat A Heat energy is used for cooking.
Answers
Heat energy is used for cooking.
It can be transferred in three ways.
3. Fill in the correct missing words: radiation,/ convection, / conduction.
(a.) In ……… heat is transferred directly from one molecule to another.
(b.) With ……….., liquids and gases create currents transferring heat to the food.
(c.) In ………. heat travels from one object to another in waves or rays e.g. barbeque, grill or microwave.*
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SAY When baking bread in the oven, there are two methods of transfer. Movement of air molecules in the oven set up convection currents and so one method is convection, but also heat energy is transferred from heated air to the baking tin and then to the cake and so the other method is conduction. Grilling meat would be radiation from the gas flame or electric element. Whereas convection and conduction are methods where heat is transferred through a medium which can be a gas, liquid or solid, radiation passes through space or a vacuum by means of electromagnetic rays. Cooking can be very scientific! ^PAUSE=1300^
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4. Moist Methods of CookingA
Answers
Moist methods involve heat being applied through liquid such as water, milk, steam, stock, wine, etc.
This method uses relatively low temperatures over a long period.
pressure cooking
stewing & braising
poaching
4. Suggest the moist method of cooking for the following foods. (There may be more than one).
(a.) white fish
(b.) potatoes
(c.) brisket of beef
(d.) eggs
(e.) meat pudding
(f.) apples. *
simmering
steaming
boiling
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SAY You need to consider the physical and working characteristics of the food when deciding which method of cooking to use. For instance, meat and fish are both food commodities that can be cooked using a moist method. Both have a substance called collagen which holds the bundles of muscle fibres together but these dissolve when heated to gelatine but meat also has elastin which binds the muscle together which does not dissolve. This holds meat together while being cooked while fish flakes and tenderises in a short time. That is why meat can be cooked over a long period and fish, being rather delicate, is best cooked by using a gentle but quick method. Root vegetables such as turnip and swede go well in a casserole to make them soft and digestable whereas leafy green vegetables need to be cooked quickly in small amounts of water to prevent vitamin loss. ^PAUSE=1300^
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5. Dry Methods of Cooking A
Answers
In dry cooking as with these sausages in a commercial oven, heat is applied directly onto food.
High temperatures are often used in dry cooking which have particular effects on the appearance and characteristics of food.
5. Give two examples of methods of dry cooking.
6. What effect does dry cooking have on bread? *
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SAY Aar! The aroma of baking bread! Dry cooking produces the most wonderful aromas. Baking bread and roast meat. The smells from cooking makes food very tempting. Dry methods of cooking involve high temperatures of up to two hundred and forty celcius for foods that need quick cooking like puff pastry or for browning meat or vegetables. In an oven it is possible to to cook at cool temperatures for foods that need cooking slowly such as rich fruit cake. Dry cooking gives food a special flavour although it can lead to food drying out. The nutritional value of protein, carbohydrates, fats and minerals are not affected but some vitamin C and thiamin are lost as they are heat sensitive.
Barbecueing food over charcoal like kebabs, burgers and meat, gives added flavour to the food especiaaly if basted in a moist marinade.USE=1300^
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6. Frying A Heat is applied through fats or oils.
Answers
Heat is applied through fats or oils.
There are four types of frying that depend on the amount of fat used and the speed of cooking.
7. Name two of these types of frying.
8. What is the main effect of frying on the nutritive value of food? *
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SAY Stir frying involves very little oil and the ingredients are finely chopped and cooked quickly so that few nutrients are lost.
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7. Microwave Cookery A
Answers
9. From the list of foods below, which food cannot be cooked by microwaves and explain why not.
Cake
Pizza
Roast chicken
Jacket potato
Peas
Whole egg.
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SAY Some foods are not so appertizing when cooked in a microwave. It is not possible to make food crisp in an ordinary microwave so food may not develop their characteristic flavours, colours or textures. Chicken will remain pale and cakes will not be golden brown and crisp on top. There are many advantages which include that they cook food quickly, they are idea for prepared foods and there is less destruction of nutrients. Vegetables are ideal as there colour and flavour can be improved. ^PAUSE=1300^
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10. Which of the above foods can be cooked in a microwave oven but this may not be appropriate? Say why not. *

8. Preserving Nutrients A
Answers
Vegetables and fruit contain the water soluble vitamins B and C which dissolve into cooking water.
This loss can be minimised by careful preparation and cooking.
11. Give three ways to minimise this loss when preparing, cooking and serving a green leaf vegetable.*
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9. Macro-Nutrients & Heat
Answers
Macronutrients are protein, carbohydrates and fats.
Heat changes their structure and characteristics
12. What is the term used when protein is permanently changed by heat?
13. What is the term used when protein sets during cooking e.g. when an egg cooks?
14. What happens to starch grains during the process of gelatinization and why is this useful?
15. What happens if fat is heated to very high temperatures? *
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10. Acids in Cooking A
Answers
Acids can change the flavour, appearance, texture and nutritional value of food.
16. Name one use of citric acid (lemon juice) in cooking.
17. In what foods would you use acetic acid (vinegar)?
18. Why is lactic acid used in cheese making? *
Ascorbic acid is added to flour to improve the dough for making bread. It helps develop the gluten formed when protein and water is mixed. The gluten of flour can stretch and when heated, coagulates, holding pockets of air which gives bread its texture.

11. Alkalis A Alkalis are used in cooking as raising agents.
Answers
Alkalis are used in cooking as raising agents.
There are 3 types of chemical raising agents:
Bicarbonate of soda
Bicarbonate of soda with acid
Baking powder.
19. Why are raising agents used?
20. Why is bicarbonate of soda used only for strong flavoured mixtures e.g. gingerbread?
21. Which raising agent would you use for scones and why? *
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SAY Bicarbonate of soda produces soda, steam and carbon dioxide but leaves a strong alkaline taste. Bicarbonate of soda and acid (sour milk or cream of tartar) which prevents the alkaline taste. Baking powder which is a mixture of bicarbonate of soda and acid and therefore convenient to use.
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12. Suggested Answers
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1. It improves and enhances flavour, gives aroma, texture, smell, improves appearance, tenderises, gives variety.
2. It kills harmful bacteria, and preserves to stop decay.
3. (a.) conduction, (b.) convection, (c.) radiation.
4a. Poaching, b. boiling/simmering, pressure cooker c. stewing d. simmering/boiling/poaching e. pressure cooker, steaming, f. stewing.
5. Baking, roasting, grilling, toasting, barbecuing.
6. Crispy top, browning or dextrinisation of starch, moist inside, brings out flavour, appetising aroma.
7. Dry frying, shallow frying, deep fat frying, stir frying.
8. Some fat is absorbed increasing energy value.
9. Whole egg. It will explode.
10. Roast chicken (unappetising appearance), cake lacks crispy top, pizza can go soggy etc.
11. Tearing, not cutting leaves, cook with lid on, minimum amount of water and time, use vegetable water for gravy, steam not boil, eat immediately. *

13. Suggested Answers continued
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Suggested Answers continued
12. Denaturation.
13. Coagulation.
14. They burst, absorb water and thicken the liquid for sauce etc.
15. Will start to decompose and burst into flames called the flash point.
16. Helps jam set, prevents enzymatic browning, coagulates protein in cold desserts.
17. In pickling, to marinate meat in salad dressing.
18. It is used in the cheese making process to coagulate milk.
19. Gives a light, airy texture.
20. It leaves an unpleasant soda taste and a yellow discolouration.
21. Bicarbonate of soda and acid (e.g. sour milk), as baking powder is not strong enough. *