Section Two - The Science Of Food

Question 1

How does cooking food make it safe to eat?

Answer 1

Many food sources contain harmful bacteria these bacteria can be killed if food is cooked at a high temperature.

Question 2

How does cooking food allow it to have a longer shelf life?

Answer 2

When food are cooked at high temperature bacteria and mould are destroyed.
This is a method of preserving the food (pasteurising milk)

Question 3

How does cooking food make allow it to develop flavours?

Answer 3

Chemical reactions take place when cooking which can change flavour. E.g. caramelisation
Roasting meats and vegetables makes the food browner and crispier with more fat added to it and water evaporates from it
It also allows flavours from different foods to blend

Question 4

How does cooking food improve texture?

Answer 4

Makes it easier to chew and digest food
Veg become softer. Pasta swells as their starch molecules soften
Meats become tender, solid fats melt and proteins denature
Other foods firm, egg whites coagulate
It can make foods more pleasant to eat. Roast potatoes, baked bread

Question 5

How does cooking food add variety to the diet ?

Answer 5

Foods can be cooked in different ways to create variety.

Beef can be cooked in so many different ways

Question 6

What is conduction?

Answer 6

The transfer of heat through the vibration of particles.
Particles in the pan nearest to the flame begin to vibrate, they knock into the particles above them further away from the heat. This continues until the pan is hot. And food placed in the pan will have heat energy put into it through the pan.

Question 7

What is convection?

Answer 7

It is the transfer of heat energy through gases or liquids.
In a pan the water nearest the heat source will get heated first, it rises. Colder water takes its place and gets heated, it rises. This process repeats until all the water is hot

Question 8

What is radiation?

Answer 8

Radiation is the transfer of heat through waves of radiation
No direct contact between heat source and food.
They emit waves of radiation which are absorbed and heat the food up

Question 9

What is Boiling?

Answer 9

Boiling involves cooking food by heating it in a pan of boiling liquid, usually water.
Examples are meat, potato, rice, pasta and veg
Not all foods can be boiled as the bubbles would break apart the food
Healthy way of cooking, however water soluble vitamins in veg are lost
Boiled food is not usually as attractive or tasty

Question 10

What is steaming?

Answer 10

Steaming means cooking food with steam from boiling water or stock.
Examples are fish, rice and vegetables
This is the healthiest way of cooking as there is no direct contact with water so water soluble vitamins remain.
It is a delicate method that doesn’t add much flavour to the food

Question 11

What is blanching?

Answer 11

Blanching involves part cooking food in boiling water for a very short time before putting it in ice water.
It stops the cooking process and preserves colour, flavour and vitamins
Blanching causes the skins on tomatoes to shrivel.
Used to prepare fruit and veg for freezing.

Question 12

What is simmering?

Answer 12

Simmering is when food is cooked at a slightly lower temperature, just below boiling
Examples are soups and curries
Simmering preserves more nutrients than boiling

Question 13

What is poaching?

Answer 13

It involves cooking food in a pan below boiling point (80c)
Examples are eggs,fruit and fish.
It helps to keep the food tender
Like with boiling nutrients and flavour are lost to the water
If food is poached in an edible sauce it can enhance the flavour

Question 14

What is braising?

Answer 14

Involves slowly cooking food in an ovenproof pot that has the lid on and contains liquid.
Used for large joints of meat because the slow cooking tenderises it
Before it is braised food is usually lightly fried to seal in the flavours.
Flavours from the liquid are absorbed by the meat

Question 15

What is stir frying?

Answer 15

Stir frying tends to be done in a wok coated in a small amount of oil.
Examples are noodles, veg, tofu and small pieces of meat and fish
It cooks quickly so must be moved round frequently to stop it from burning.
Vegetables keep more nutrients, taste better with the added fat

Question 16

What is shallow-frying?

Answer 16

The pan is coated in a medium amount of oil
Examples are chops, bacon and sausages
It is a less healthy option than stir frying due to the oil, solid fats in the food also melt
Shallow frying also gives food a more crispy texture

Question 17

What is sweating?

Answer 17

It releases moisture from food making it sweeter and more tender.
A small amount of oil is put into a pan with the vegetables. It is put over a low heat where it sweats

Question 18

What is baking? What are the benefits and disadvantages to it?

Answer 18

It cooks food using dry heat.
Examples are bread, pastries, cake, fish and meats
Modern electric ovens circulate the air using a fan which keeps the whole oven at a similar temperature, it heats the oven up faster
Its healthy, tastes better, crisps up
It takes a long time, can dry out and uses a lot of energy as the oven has to remain on for a long time

Question 19

What is grilling? What are the advantage and disadvantaged?

Answer 19

It uses a dry heat at a higher temperature when baking or roasting.
As it grills fats drip out of the food becoming golden and crispy
Example are meats, vegetable and cheeses
Foods cook quickly, fairly healthy, it looks and tastes nice, smoky flavour
Hard to cook evenly, burning easy, handling raw and cooked meat on a bbq could lead to cross contamination, easy too cook out but not in.

Question 20

What is roasting? What are the advantages and disadvantages?

Answer 20

Like baking roasting uses dry heat from ovens.
It is usually done at higher temperatures than baking and fat is added e.g. oil or fat from chicken put back on chicken (basting)
Extra fat and high temperatures crisp and brown which tastes great, the fat from roasted meat can be used to cook other food (potatoes)
Roasted food isn’t always healthy as extra fat is often added, it takes a long time and uses a lot of energy

Question 21

What is dry frying?

Answer 21

It means cooking food in a pan without oil or fat.
Dry fry food like bacon which contain natural fat which cooks food
Dry roast seeds, nuts and spices
No extra fats or oils are added making this method healthier
Dry roasting can improve the taste of spices
It takes longer, it can only be used for foods with a high fat content

Question 22

What does it mean for proteins to denature? Examples of methods?

Answer 22

It means chemical bonds holding their structure together break down, the proteins unravel and their shape changes mostly irreversible.
Whisking, beating and kneading, physical agitation
Heat, changes in temperature
Acids, lemon juice and marinades

Question 23

What does it mean for protein molecules to coagulate?

Answer 23

Once denatured the protein molecules collide with other protein molecules and coagulate.
During this water becomes trapped between the molecules.
It changes the texture, taste and appearance of food, egg whites and steak
Over coagulation turns the food rubbery and dry.

Question 24

How are foams formed through coagulation?

Answer 24

Foams are formed when gas becomes trapped within the liquid.
When the proteins coagulate (egg white) air becomes trapped in the proteins.
Over whisking causes the air to escape
Egg whites become meringue

Question 25

What is gluten?

Answer 25

Gluten is a protein found in wheat flours It is formed when water is mixed with the flour to make dough. Molecules of gluten are coiled which allows them to stretch and bend When the dough is baked the gluten stays coagulated and the dough stays stretched, it gives well risen bread a light, airy texture.

Question 26

What is gelatinisation?

Answer 26

It helps to thicken foods that contain starch e.g. sauces, custards and gravies. When starch granules are first mixed with liquid they becomes suspended in it. When they are heated with water the starch granules swell in size and soften. Between 62 and 80 degrees the granules burst and release their starch. This thickens the liquid. How thick depends on the ratio of water to starch. When it cools it solidifies and a solid gel is formed.

Question 27

What is dextrinisation?

Answer 27

When starchy food are cooked with dry heat.toasting. The starch molecules in the food breaks down into smaller molecules called dextrins. It gives the food a browner, crispier texture as well as a different taste

Question 28

What is caramelisation?

Answer 28

Sugar molecules break down when they reach a high temperature, it causes sugar to break down and change flavour. The sugar goes through various stages, it changes from a very sweet runny liquid to a smooth caramel eventually developing a hard candy like texture it can burn easily.

Question 29

What is aeration?

Answer 29

When fats such as butter are beaten with sugar air becomes trapped in the mixture. This air makes the mixture fluffier and lighter. It gives cakes a spongy light texture. Whisking or quickly beating with a spoon

Question 30

What is shortening?

Answer 30

When you rub fat into flour you cover the flour particles with a waterproof coating. It prevents long gluten molecules forming when water is added to flour. It means that dough cannot become stretchy and baked good like shortbread remain crumbly

Question 31

What is plasticity?

Answer 31

It means we are able to spread and manipulate them. This is possible because fats contain a mixture of different triglycerides which melt at different temperatures, so fats gradually soften over a range of temperatures. Unsaturated fats are more liquid. It is useful for decorating cakes with icing or shortening dough

Question 32

What is emulsification?

Answer 32

They are formed when oily and watery liquids are shaken together. Milk, margarine and mayonnaise are examples They separate out after a while unless a emulsifier is used When you add an emulsifier the water molecules bond to one end and the oil bonds to the other end keeping them in a stable emulsion.

Question 33

How can you use emulsions for sauces and salad dressings?

Answer 33

Hollandaise sauce is an example of an emulsion sauce. Melt the butter in the pan Mix the egg yolks and lemon juice in a bowl Gently warm the mix by placing the bowl over a pan of simmering water Slowly add the melted butter constantly whisking Keep whisking the sauce until smooth

Question 34

If making a oil in water emulsion you should...

Answer 34

Add the liquid and emulsifier first before very slowly adding the oil/fat while mixing vigorously

Question 35

How does bicarbonate of soda work as a chemical raising agent?

Answer 35

When its heated it breaks down to produce carbon dioxide bubbles that expand to make the mixture rise. It has a strong alkaline taste so is used in things like cake Baking powder is a mix of bicarb of soda and cream of tartar. A neutralisation reaction takes place when its heated.

Question 36

How does yeast work as a biological raising agent?

Answer 36

Used in bread dough. It is a bacteria that causes fermentation- a process that releases alcohol and co2 When a dough is left to prove it is when the carbon dioxide is released and trapped in the dough, causing it to rise it stops during baking as the yeast is killed by the heart. when the dough is baked the carbon dioxide expands and alcohol evaporates

Question 37

An example of a raising agent that adds steam to the mixture?

Answer 37

When you use a very hot oven to cook a mixture that deliberately contains a lot of liquid water leaves the mixture as steam, as the steam rises it raises the mixture up. The food bakes and becomes solid. Keeping the door closed is essential to keeping the mixture plump as cold air causes the mix to sink.

Question 38

What is a mechanical example of adding air to a mix?

Answer 38

Air can be folded into mixtures in two different ways: - to fold a cake mixture you repeatedly pour the mix over itself - pastry doughs can be folded over each other trapping air in the layers Beating is a more vigorous method where you use a spoon or fork to quickly drive air into a mixture. Sieving flour traps sir in the flour particles, creaming traps air too

Question 39

How does yeast make alcoholic beverages?

Answer 39

During the fermentation process, yeast converts sugar into carbon dioxide and ethanol, the co2 can be left to add fizz but can also be removed

Question 40

How does yeast get used to make bread?

Answer 40

Yeast is added to flour and water to form a dough. Salt is added for flavour, but also to strengthen the gluten in the dough The gas produced is what causes the bread to rise

Question 41

Why do people add mould to cheese?

Answer 41

The blue bits on blue cheese are due to moulds that have been added. The mould gives the cheese a creamy texture and a distinctive sharp, tangy taste.

Question 42

How are bacteria used in yogurt n' cheese?

Answer 42

The bacteria ferment lactose and produce lactic acid The lactic acid acts on the protein in the milk to thicken it and gives it a sour or tangy taste Probiotics are a supplement in some yogurts which are said to give health benefits

Question 43

How are bacteria used to make fermented meats?

Answer 43

Raw meat is mixed with a combo of ingredients including salt, sugar, flavourings and a starter culture of bacteria. The bacteria ferment the sugar and produce lactic acid this lowers the ph causing the proteins in the meat ti denature and coagulate forcing the water out, the low oh and water mean bad bacteria cant grow