Food Science

Question 1

Why food is cooked

Answer 1

To make is safe to eat
To  improve the shelf life
To develop flavour
To improve texture
To give variety in the diet

Question 2

Why food is cooked- to make it safe

Answer 2

Many food sources (meat, poultry, eggs) can contain harmful bacteria that make us sick. At a high temperature, this bacteria can be killed.

Some foods contain harmful toxins that are destroyed when cooked, eg red kidney beans.

Question 3

Why food is cooked - to improve shelf life

Answer 3

When cooked at high temperatures, bacteria and mould are destroyed. So food can be preserved in this way during the manufacturing process, eg. milk is pasteurised (heated to a high temp) to help it to stay fresh for longer.

Question 4

Why food is cooked - to develop flavour

Answer 4

Chemical reaction take place during cooking which changes the flavour. eg. caramelisation can occur when onions are cooked, making them sweeter.

Roasting meats and vegetables creates a more intense flavour, becomes more brown and crispy as more fat is added and as water evaporates.

Cooking also allows different flavours to combine eg. braising meat in a pot of liquid and vegetables.

Question 5

Why food is cooked- to improve texture

Answer 5

Cooking usually makes it easier to chew, swallow and digest our food.

Some foods turn softer when cooked, eg broccoli or carrots, rice and pasta swell as their starch molecules soften.

Meats become more tender as the solid fats melts and the proteins in the meat denature.

Other foods become firm when cooked eg proteins in egg whites coagulate, but can become ruberry when overcooked.

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Question 6

WHy food is cooked - to give variety

Answer 6

Food can be cooked in different ways, which creates a variety in the diet. eg can grill, roast make a stew all out of beef.

Question 7

Cinduction

Answer 7

Transfer of heat energy through thr vibration of particles.

IN a solid the particles are held tightly together, and when it vibrates they bump into the particles next to them.

When a pan is heated, heat energy from the hob causes particles in the pan to vibrate and gain heat energy. These particles then vibrate and collide with the neighbouring particles, transferring some heat energy. This process continues until the whole pan has been heated.

This happens again when food is placed into the pan - heat energy is transferred through the colliding of particles.

Metals are good conductors of heat so are used to make pans so the energy is transferred quickly.

Question 8

convection

Answer 8

This is the transfer of heat energy through gases or liquids.

When you heat up a liquid, the liquid near the heat source warms up quicker. the warmer liquid rises, and the colder liquid takes its place. Then the colder liquid is heated, begins to rise so cold liquid takes its place.

As this process continues you end up with a circulation of fluid (convection currents), and after a while this circulation of heat results in the whole fluid being heated.

Convections also occurs in ovens, the hot air rises, cooler air falls.

Question 9

Radiation

Answer 9

This is the transfer of heat energy through waves of radiation.

There is no direct contact between the heat source and the food.

Grills and toasters use radiation to cook food

They emit waves of radiation, which are absorbed by the food and heat it up.

Microwaves use radiation to heat up fat, sugar and water molecules in our food.

Question 10

Boiling

Answer 10

Cooking food in a pan of boling liquid, usually water.
eg, meat, potatoes, rice, pasta

Quite harsh and can’t be used on delicate foods as the bubbles would break up the food.

Overboiling foods like pasta can cause them to become too soft.

Healthy, as no fat is added. However, veg can lose colour, flavour and water soluble vitamins which are lost in the water.

Often not as tasty as roasted food, for example.

Boiling foods with a small amount of water with a lid uses less energy than other methods.

Question 11

Steaming

Answer 11

Cooking food with steam from boiling water or stock.

Can steam fish, rice, vegetables.

No fat is added, no direct contact with the water.

Veg keep more of their taste, texture, colour and nutrients than boiling, so it is the healthiest way to cook. Still not much flavour compared to frying or roasting.

Gentle way to cook, good method for delicate foods such as fish but not tough meats.

Question 12

Blanching

Answer 12

Part-cooking the food in boiling water for a short time before putting it in cold or iced water.

The cold water stops the cooking process, which helps preserve colour, texture and vitamins.

Can be used to remove harsh flavours, eg raw onions to give them a milder taste.

Blanching foods like tomatoes and almonds makes their skins shrivel up making the easier to remove.

Also used to prepare fruit and veg for freezing.

Question 13

Simmering

Answer 13

Similar to boiling, but more gentle as the temp is slightly lower than boiling point.

Common cooking method for soups or curries.

Preserves more nutrients than boiling.

Question 14

Poaching

Answer 14

Cooking food in a pan of liquid below boiling point, around 80 degrees.

Can poach eggs, fruit and fish.

Gentle way to cook, helps keep food tender. Nutrients and flacours are transferred to the liquid lowering the nutritional content and tastiness of the food.

But if it is poached in a sauce this can give the food a variety of flavours.

Question 15

Braising

Answer 15

Slowly cooking the food in an ovenproof pot with a lid on which contains a liquid (water, stock or wine) and often herbs and vegetables.

Food is cooked in the pot through a mixture of simmering and steaming.

Good for bug tough joints of meat, gentle cooking helps to tenderise it,

Usually lightly fry the food before to brown and seal it, to help keep the juices inside and to give a caramelized flavour.

Flavours from the liquid and any vegetables in the pot are absorbed, adding flavour.

Question 16

Stir-frying

Answer 16

Often done in a wok, coted in a small amount of oil making it quite healthy.

Foods eg noodles, vegetables, tofu, small pieces of meat or fish.

Foods cook very quickly and needs to be moved around constantly to prevent burning. Since they’re cooked quickly, vegetables keep more of their nutrients.

Stir fried meals often have more vegetables and little meat, making them a healthy option.

Question 17

Shallow frying

Answer 17

Frying pan coated in a medium amount of fat or oil.

Can cook meat, fish, eggs, pancakes.

More fat is used so it is a less healthy way of cooking. Solid fats melt into the pan as the food cooks, increasing the amount of fat in the pan.

This gives a crispier texture than stir frying.

Question 18

Sweating

Answer 18

Releases moisture from food, making it more tender and sweet-tasting.

Most often used for vegetables, eg onions, and uses a small amount of oil over a low heat. the low heat allows the food to release moisture without browning

Food usually covered with a lid to help the moisture circulate.

Question 19

BAking

Answer 19

Cooks food using dry heat usually in an oven.

Bake bread, pastries, cakes, potatoes, whole fish.

Meat can be baked in meatloaf or casseroles.

Food cooks quicker on the top of the oven as hot air rises.

modern ovens are often fan assisted, which helps the hot air circulate around the oven. this means to food bakes more evenly as all parts of the oven are a similar temperature, and the oven heats up quicker meaning your food cooks quicker, using less energy,

Question 20

Advantages and disadvantages of baking

Answer 20

Advantages:
Wide variety of food can be baked.
Outside browns and crisps up which looks and tastes nice.
Quite healthy as no extra fat is added, and solid fats in the food often leave the food as it is baked.

Disadvantages:
Can take a long time.
Food can become dried out.
Requires a lot of energy to keep the oven at a high temperature for a long time.

Question 21

Grilling

Answer 21

Uses dry heat at a higher temperature than baking or roasting to cook food.

As food is grilled fats drip out of the food and the outside becomes golden and crisp.

Barbequing is similar to grilling, but heat radiates from hot coals and food is cooked at a lower temperature for longer.

Can grill smaller bits of meat, vegetables and cheese.

Question 22

Advantages and disadvantages of grilling

Answer 22

Advantages:
Food cooks quickly at a high temperature.
Fairly health as no fat is added and the fat in the food drips away when cooking.
Leaves the outside golden, which looks and tastes nice.
Gives a crispy texture.
Grilling on a barbecueue gives a smoky flavour which is popular.

Disadvantages:
High heat used makes it hard to cook the food evenly.
Easy to burn the food, or to end up with a cooked outside but raw inside, which could lead to food poisoning.
handling both raw and cooked meat on a barbecue could lead to cross-contamination.

Question 23

Roasting

Answer 23

Roasting uses dry heat from the oven.
This is usually done at a higher temperature than baking so foods cook and brown more quickly

Fat is often added to the outside of the food eg. Potatoes or veg, to help it brown and stay moist. Fat can be added or the fat that has melted from the food can be put back on top - this is called basting.

Normally roasts large cuts of meat, potatoes, vegetables and chestnuts.

Question 24

Advantages and disadvantages of roasting

Answer 24

Advantages:
Extra fat and a high temperature helps the food to brown and crisp the outside of the food, which looks and tastes delicious.
The fat from the roasted meat can be used to cook other food
Roasted food can be tasty and moist.
Roasting can produce meat with a rare centre, which lots of people like.

Disadvantages:
Roasted food isn’t that healthy as extra fat is often added.
It takes a long time and uses lots of energy.

Question 25

Dry frying

Answer 25

Cooking food in a pan without fat or oil
You can dry fry foods that contain natural fat eg minced meats and bacon. As the food heats up, the fats inside the food melt into the bad and begin to cook the food.

Nuts seeds and spices can also be cooked in this way, but this method is often called “dry roasting”. This helps to release oils oils and bring out more flavour in the food.

Using a medium heat is important at the start of cooking to allow the fats to melt without burning the food. Once the fat melts the temperature can be increased as the fat starts to fry the food.

Question 26

Advantages and disadvantages of dry frying.

Answer 26

Advantages:
No extra fats or oils added, making this method healthier than other frying methods.
Dry roasting can be used to give a more distinct aroma to nuts, seeds and spices.

Disadvantages:
Takes longer than other frying methods to cook meat thoroughly, as lower temperatures are needed at the start.
Can only be used for a small range of food types compared to other cooking methods.

Question 27

Protein desaturation

Answer 27

Proteins have a complex structure. When cooked, proteins denature - when the chemical bonds holding their structure together break down.

The proteins unravel and their shape changes- in most cases this is irreversible.

Proteins can be denatured through:
Physical agitation (whisking, besting and kneading)
Changes in temperature (heat)
Acids (lemon juice and marinades)
Acidic marinades denature the protein before cooking which makes the meat more ended before cooking.

Question 28

Coagulation

Answer 28

Once they have denatured, protein molecules collide with other protein molecules and coagulate (join together)

During this process, water becomes trapped between the protein molecules.

Coagulation changes the appearance and texture of the food eg egg which turns from a see through liquid into a white solid steak becomes brown, firmer and easier to eat as you cook it.

If food is over cooked and coagulation happens too much, the protein tightens. This forces water out of the molecules, making it dry and chewy.

Question 29

Foams

Answer 29

Foams (chocolate mousse, whipped cream, cappuccino foam) forms when gas becomes trapped inside liquid.

When liquids containing proteins are agitated, the proteins inside the liquid denature which causes them to stretch and air to become trapped in the liquid.

When the proteins coagulate, this air becomes trapped creating a foam.

Overwhisking causes these new protein bonds to brea- air escapes and the foam collapses.

Some foams form a solid structure when they are cooked, eg white foams become meringues.

Question 30

Gluten

Answer 30

Gluten is a protein found in wheat flours.

It is formed when water is mixed with the flour to make a dough, can be found in foods like bread, pasta, cakes and pastries.

Molecules of flute are coiled, which means they are able to stretch and bend which gives all doughs elasticity.

Strong flour forms more gluten than other types.

Doughs need to be needed to “work” the gluten, which causes gluten strands to get longer, stronger and stretchier.

When it reaches a high temperature, gluten coagulates and the dough stays stretched. this gives foods like well-risen bread a light, airy texture.

Question 31

Starch gelatinisation

Answer 31

Thickens liquids.
Gelatinisation helps to thicken foods that contain starch.
When starch granules are first mixed with liquid, they become suspended in it - stirring prevents them from sinking to the bottom.

When the granules are heated with water, the bonds between the starch molecules start to break, allowing water molecules to enter. As water is absorbed, the starch granules swell in size and soften.

Between 62 and 80 degrees c the granules burst open and release their starch into the liquid. This causes the liquid to thicken - how much it thickens depends on the ratio of starch to liquid in the mixtire.

When it cools the liquid solidifies and a solid gel is formed. used for making set desserts like custards or lemon pie filling.

Gelatinisation also happens when you cook starchy foods like pasta and rise - they swell, soften and release starch into the water as they cook.

Question 32

Dextrinisation

Answer 32

When starchy foods (bread, biscuits) are cooked with dry heat the starch molecules in the food break down into smaller molecules called dextrins.

This breakdown is called dextrinisation and gives the food a browner colour and a different taste.

The longer the food is cooked, the more starch is converted into dextrin and the darker and crispier the food becomes.

Question 33

Caramelisation

Answer 33

Sugar molecules break down when they reach a high temperature, which causes sugar to turn brown and change flavour. This is caramelisation.

As first, the liquid is runny and has a sweet taste.
Then it becomes more smooth, like caramel.
eventually, it turns harder as is coold.

Caramelised sugar can burn very quickly, turning black, brittle and bitter. To avoid this water is often added during the early stages of heating.

Caramelisation gives desserts such as creme brulee and apple pie extra sweetness. Savoury foods which contain sugars, such as onions. can also caramelize. The sugars are broken down and realeased, turning the food brown and adding sweetness.

Question 34

Aeration

Answer 34

When fats and butter are beaten with sugar (creaming), air becomes trapped in the mixture. the air makes the mixture fluffier and lighter in colour.

This aeration gives cakes a spongy and light texture when cooked.

Foods can be aerated through whisking (eg. egg whites) or quickly beating with a spoon.

Question 35

Shortening

Answer 35

When you rub fat into flour, you coat the flour particles with fat, giving it a waterproof coatin.

This prevents long gluten molecules forming when water is added, which means the dough cannot become stretchy and baked goods (shortbread) remain a short texture.

Shortening is used when making filled pies and tarts so the base doesn’t rise and instead forms a solid case.

Some fats are called shortening, which contain 100% fat content (no water) to stop gluten formation and to prevent steam from raising the food.

Question 36

Plasticity

Answer 36

Ability to be spread and shaped - fats have plasticity.

They contain a mixture of different trigcerides, which all melt at different temperatures, so fats gradually soften over a range of temperatures rather than melting at just one.

The more plasticity a fat has, the easier it is to spread

The more unsaturated fatty acids a fat has the more plasticity it will have.

Question 37

Uses of plasticity

Answer 37

Decorating cakes with buttercream
Rubbing fat into flout to shorten the dough.
Spreading butter on sandwiches or toast
Putting cream cheese on crackers.

Some vegetable fats are ‘easy to spread’ because they contain a mixture of triglycerides with low melting points meaning you can spread it as soon as you take it out of the fridge.

Question 38

Emulsification

Answer 38

Emulsions are formed when oily and watery liquids are shaken together (the droplets of one spread out through the other).

Milk, margarine and mayonaise are all examples of emulsions.

Usually, oil and water don’t mis, so they separate out unless you use an emulsifier.

Emulsions can be oil in water eg. milk, mayonaise or water in oil, eg margarine. butter

Question 39

What are emulsifiers

Answer 39

Molecules in an emulsifier have two different ends - one is hydrophilic (acttracted to water) and one is hydrophobic (repulsed by water).

When you add an emulsifier, the 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, preventing them from separating.

Question 40

Egg yolks - emulsification

Answer 40

Egg yolks contain a natural emulsifier - lecithin (also found in soya). this is used as the emulsifier in margarine and mayonaise.

Mayonaise is a stable emulsion of egg yolk, oil and vinegar. when making stable emulsions you must make sure you add the oil or water gradually and mix the ingredients for long enough.

Question 41

Emulsions in sauces or salad dressings

Answer 41

Often used in sauces or salad dressings.

Hollandaise sauce is an amulsion sauce - made from butter, water, egg yolks and lemon juice.

When making oil-in-water emulsion, you must add the liquid and emulsifier first, then slowly add the fat/ oil while mixing vigorously.

Question 42

Hollandaise sauce recipe

Answer 42

Melt the butter in a pan.

Mix the egg yolks and lemon juice in a bowl.

gently warm the mixture by placing the bowl over a pan of simmering water.

Slowly add the melted butter, constantly whisking as you do.

Keep whisking until it is all mixed together smoothly.

Question 43

Chemical raising agents

Answer 43

Bicarbonate of soda- when heated produces carbon dioxide bubbles that expand to make the mixture rise.
Has an unpleasant alkaline taste, so needs to be used with a strong flavour to mask it eg. ginger.

Baking powder- mixture of bicarbonate of soda (alkali) and cream of tartar (acid). A neutralisation reaction takes place which gets rid of the alkaline taste.

Self raising flour contains a mixture of plain flour and baking powder.

Question 44

Biological raising agents - yeast

Answer 44

its a microorganism that causes fermentation - a process that releases alcohol and carbon dioxide.

Doughs containing yeast are often proved - left in a warm place to allow fermentation to take place. This is 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.

When the dough is baked, the carbon dioxide explands, causing the bread to rise more, and any alcohol produced by the yeast evaporates.

Question 45

Raising agents - steam

Answer 45

using a hot oven to cook a food which contains lots of liquid (batters, puff pastry, coux pastry) 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. it is important to keep the oven door closed so the cold air from outside will not cause the mixture to sink/

Question 46

Raising agents - mechanical

Answer 46

Air can be folded into mixtures and doughs.

You can fold it in eg. into a cake mixture, by carefully using a spoon or spatula to pour the mixture over itself, trapping air each time.

Pastry doughs can be folded into layers, trapping air between the layers.

Beating/whisking is more vigourous and quickly drives air into the mixture.

WHen you sieve flour air becomes trapped between the individual flour particles.

Air is added when creaming, and between flour particles when you rub fat in,