Section 2: Food Science

Question 1

Why do we cook food to make it safe to eat? it’s

Answer 1

many food sources such as meat and eggs contain harmful bacteria that makes us ill and in high temperatures these bacteria are killed

some foods contain harmful toxins that are destroyed when cooked

Question 2

Why do we cook food to improve shelf life?

Answer 2

food can be preserved in the manufacturing process when cooked at high temps because bacteria and mould are destroyed

e.g milk is pasteurised so it lasts longer

Question 3

Why do we cook food to develop flavour?

Answer 3

chemical reactions take place when we cook food that change the flavour e.g caramelisation makes food sweeter

roasting adds more intense flavour to meat and veg

cooking allows us to combine different foods

Question 4

Why do we cook food to improve its texture?

Answer 4

can make food easier to swallow as some foods become softer when cooked e.g carrots but some foods also become firmer like eggs

change in texture can make food more pleasant to eat

Question 5

Why do we cook food to give a variety in diet?

Answer 5

e.g if you are craving beef you could have grilled steak, roast beef or beef stew etc to suit your preference

Question 6

What is conduction?

Answer 6

transfer of heat energy through the vibration of particles. when particles in a solid vibrate they collide with nearby particles and pass on heat energy from the pan until the heat has passed all the way through.

Question 7

What is convection?

Answer 7

transfer of heat energy through liquids or gases. when you heat up a liquid the liquid near the heat source heats faster and the warm liquid rises above its colder surroundings. the colder liquid is heated and begins to rise the process creates convection currents. this can occur in ovens.

Question 8

What is radiation?

Answer 8

transfer of heat energy through waves of radiation. no direct contact between food and heat source. cookers emit waves of radiation which are absorbed by the food so they can heat up. grills, toasters and microwaves use this.

Question 9

How and why is water used to boil food and which foods can be boiled?

Answer 9

how -heating food in a pan of boiling liquid.

why- healthy way to cook food as no fat is added however is eg is boiled for too long water soluble vitamins can be lost in water. also uses less energy than other methods.

foods- meat, potatoes, rice, pasta, veg

Question 10

How and why is water used to steam food and which foods can be steamed?

Answer 10

how- cooking with steam from boiling water

why-healthiest way to cook as nutrients of food like veg are not lost however can be tasteless. also gentle way to cook food.

foods- fish, rice, veg

Question 11

How and why is water used to blanche food and which foods can be blanched?

Answer 11

how- part-cooking good in boiling water for s short time before putting in cold water

why- cold water stops cooking process to preserve colour, texture and vitamins. also sued to remove harsh flavours e.g raw onion

foods- tomatoes, almonds

Question 12

How and why is water used to simmer food and which foods can be simmered?

Answer 12

how- boiling but more gently as temp is slightly lower than boiling point

why-preserves more nutrients than boiling

foods-soups and curries

Question 13

How and why is water used to poach food and which foods can be poached?

Answer 13

how- cooking food in pan of liquid below boiling point (80 degrees)

why- helps keep food tender however nutrients and flavours are transferred to liquid

foods- eggs, fruit, fish

Question 14

How and why is braising used to cook food and which foods can be braised?

Answer 14

how- slowly cooking food in ovenproof pot that contains liquid. food is cooked by a mixture of simmering and steaming.

why- great for big or tough joints of meat to help tenderise it.

foods- meat with herbs and veg

Question 15

How and why is stir frying used to cook food and which foods can be stir-fried?

Answer 15

how- tends to be done in a wok that is coated a small amount to oil

why- cooks food very quickly which means veg keep their nutrients

foods- noodles, veg, tofu or small pieces of meat and fish

Question 16

How and why is shallow frying used to cook food and which foods can be shallow fried?

Answer 16

how- frying pan coated in mdid amount of fat or oil

why- gives food a crispier texture but is very unhealthy as more fat is used than stir frying and solid fats in food melt into the pan

foods- meat, fish, eggs, pancakes

Question 17

How and why is sweating used to cook food and which foods can be this be done to?

Answer 17

how- small amount of oil over low heat so food release moisture without burning

why- makes foods more tender and sweet-tasting

foods- vegetables such as onions

Question 18

What are examples of dry methods of cooking?

Answer 18

baking, grilling, roasting and dry frying

Question 19

How and why is baking used to cook food and which foods can be baked?

Answer 19

how- using dry heat usually from an oven

why- food cooks quicker due to convection, foods cook evenly

foods- breads, pastries, potatoes, whole fish

Question 20

What are the advantages and disadvantages of baking foods?

Answer 20

advantages-
The outside of the food browns and crisps up, which looks and tastes nice.
It’s quite healthy because no extra fat is added,

disadvantages-
can take a long time.
Food can become dried out.
It uses a lot of energy as it requires the oven to be kept at a high temperature for a long time.

Question 21

How and why is grilling used to cook food and which foods can be grilled?

Answer 21

how- uses a dry heat at a higher temperature than baking or roasting to cook food

why- fats drip out of the food and the outside of the food becomes golden and crisp.

foods- as: smaller bits of meat, vegetables and cheeses (like halloumi or goats’ cheese).

Question 22

What are the advantages and disadvantages of grilling food?

Answer 22

advantages-
-It’s fairly healthy
-the golden outside of the food looks and tastes nice and can have a lovely crispy texture.
-Grilling on a barbecue gives food a smoky flavour which is very popular.

disadvantages-
-high heat used when grilling can make it hard to cook the food evenly.
-It’s easy to burn the food
-handling both raw and cooked meat may lead to cross-contamination

Question 23

How and why is roasting used to cook food and which foods can be roasted?

Answer 23

how- uses dry heat from the oven at very high temperatures so foods can brown quickly

why- fat is added to the outside of the food to keep it moist

foods- large cuts of meat, potatoes, veg

Question 24

What are the advantages and disadvantages of roasting food?

Answer 24

advantages-
-Extra fat and a high temperature helps to brown and crisp food which tastes and looks better
-tasty and moist

disadvantages-
-isn’t always that healthy, as extra fat is often added.
-takes a long time to roast food and uses a lot of energy.

Question 25

How and why is dry frying used to cook food and which foods can be dry fried?

Answer 25

how- cooking food in a pan without fat or oil. use medium heat so food doesn’t burn. conduction.

why- This helps to release oils and bring out more flavour in the food.

foods- foods that contain natural fat, e.g. minced meats and bacon. Nuts, seeds and spices can.

Question 26

What are the advantages and disadvantages of dry frying food?

Answer 26

advantages-
-No extra fats or oils are added so healthier
-can be used to give a more distinct aroma to nuts, seeds and spices.

disadvantages-
-takes longer than other frying methods because lower temperatures are needed at the start.
-can only be used for a small range of food types

Question 27

How do proteins denature during preparation and cooking and what is it caused by?

Answer 27

they have a complex structure so when cooked the chemical bonds holding them together break down

caused by- changes in temp, acids, physical agitation (whisking, beating)

Question 28

How does protein coagulate?

Answer 28

once denatured, protein molecules collide and coagulate together. water becomes trapped in molecules. changes appearance and texture of food e.g eggs turn to white solid instead of see through liquid

Question 29

How are foams formed when air is trapped in food (aeration)?

Answer 29

gas becomes trapped in liquid. proteins inside liquid denature when agitated causing them to be stretched so air is trapped.

Question 30

How does gluten allow doughs to stretch and rise?

Answer 30

formed when water is mixed with the flour. molecules of gluten are coiled which gives doughs elasticity. doughs need to be kneaded to work the gluten.

Question 31

How does starch gelatinisation thicken liquids?

Answer 31

starch granules are mixed with liquid and become suspended. when heated with water starch molecules break allowing water molecules to enter. starch granules burst into liquid around 60-80 degrees making it thicker.
e.g custards, lemon pie filling, pasta, rice

Question 32

What is dextrinisation?

Answer 32

when starchy foods are exposed to dry heat. starch molecules in food break down into smaller molecules called dextrins. gives food browner colour and crisper texture.
e.g bread

Question 33

How does sugar caramelise when it is heated?

Answer 33

sugar molecules break down when they reach a high temperature causing the sugar to brown and change flavour.
e.g caramelisation makes creme brûlée and apple pie sweeter

Question 34

What is done to make sure caramelised sugar doesn’t burn too quickly?

Answer 34

water is added at early stage of heating.

Question 35

What does aeration do to food?

Answer 35

makes food a lighter colour, fluffier in texture, spongy when cakes

Question 36

How does shortening food give food a crumbly texture?

Answer 36

rubbing fat into flour gives it a waterproof coating which prevents long gluten molecules forming when water is added to flour. this means dough can not stretch.
e.g filled pies, tarts

Question 37

What is plasticity?

Answer 37

when we are able to spread and manipulate foods like fats. this is because they have triglycerides which all melt at different temperatures so gradually soften over a range of temps. the more unsaturated fatty acids a fat or oil contains the more plasticity it has.

Question 38

What can plasticity be used for?

Answer 38

decorating cakes with buttercream, spreading butter on toast

Question 39

What is emulsification and what does this occur in?

Answer 39

when oily and watery liquids are shaken together. oil and water don’t mix together so emulsions separate out unless you use an emulsifier.

e.g milk, margarine, mayonnaise

Question 40

What is are the two types of emulsifier?

Answer 40

hydrophilic - attracted to water
hydrophobic- repulsed by water

Question 41

What happens when you add an emulsifier to food?

Answer 41

water molecules bond to the hydrophilic side and the oil molecules bond to the hydrophobic side. This holds the oil and water together in a stable emulsion.

Question 42

Which natural emulsifier do egg yolks contain?

Answer 42

lecithin

Question 43

How is hollandaise sauce made?

Answer 43

1. Melt the butter in a pan.
2. Mix the egg yolks and lemon juice in a bowl.
3. Gently warm this mixture by placing the bowl over a pan of simmering water.
4. Slowly add the melted butter to the mixture, constantly whisking as you do.
5. Keep whisking the sauce until it’s all mixed together smoothly.
   When

Question 44

What is a chemical raising agent?

Answer 44

When it’s heated, bicarbonate of soda breaks down to produce carbon dioxide bubbles that expand to make the mixture rise. used in things like gingerbread and choc cake
e.g baking powder, baking soda

Question 45

What is a biological raising agent?

Answer 45

Yeast is a biological raising agent used in bread dough.
It’s a microorganism that causes fermentation - a process that releases alcohol and carbon dioxide.

Question 46

Why is dough proved (left in warm place to allow fermentation)?

Answer 46

when the carbon dioxide is released and trapped in the dough, causing it to rise - fermentation stops during baking as the yeast is killed by the heat.

Question 47

How is steam used as a raising agent?

Answer 47

When you use a hot oven to cook a mixture that contains a lot of liquid water leaves the mixture as steam. As the steam rises it raises the mixture up. As the water leaves, the food bakes and becomes more solid.

Question 48

What is a mechanical raising agent?

Answer 48

add air into mixtures by hand.
e.g. beating, whisking, creaming.

Question 49

What is fermentation of yeast used to make?

Answer 49

alcoholic beverages

Question 50

What happens during the fermentation process?

Answer 50

yeast converts sugar into carbon dioxide and ethanol. e.g. the sugars in grapes are used to ferment wine.

Question 51

How are fermented meats made?

Answer 51

combination of salt, sugar, flavourings and a ‘starter culture of bacteria’. the bacteria ferment the sugar and produce lactic acid which lowers the PH of the meat. proteins in the meat denature and coagulate forcing water out of the meat.

Question 52

Why are fermented meats safer to eat for longer?

Answer 52

low Ph and lack of moisture which makes it harder for pathogenic bacteria to grow