Section 2- Food science Flashcards
1
Q
Why is food cooked?
A
- to make it safe to eat
- to improve shelf life
- to develop flavours
- to improve texture (makes it easier to chew and swallow)
- to give variety in the diet
2
Q
What is conduction?
A
- transfer of heat energy through vibrations of particles
- in a solid the particles are held tightly together - when one particle vibrates it bumps into other particles and passes vibrations on
- when a pan is placed on a hob, heat energy from the hob causes particles in the plan to vibrate more and more and gain heat energy
- when these particles collide with nearby particles, they pass some of their extra heat energy onto them
- this process continues throughout the pan, until heat is passed all the way through
3
Q
What is convection?
A
- transfer of heat energy through gases or liquids
- heat up a liquid- the liquid near the heat source warms up faster
- the warmer liquid rises, colder liquid takes its place
- colder liquid is heated and when it starts to rise, colder liquid takes its place
- this process continues and you end up with a circulation of fluid (convection current)
4
Q
What is radiation?
A
- transfer of heat energy through waves of radiation
- unlike conduction and convection- no direct contact between the heat source and the food
- cookers like grills and toasters use radiation to cook food
- emit waves of radiation - when these waves reach the food, they are absorbed and heat the food up
- microwaves use radiation to heat up the fat, sugar and water molecules in out food
5
Q
What is boiling?
A
- involves cooking food by heating it in a pan of boiling liquid, usually water
- harsh method of cooking - cant be used on delicate foods
- healthy way to cook as no fat is added (if veg is boiled for too long, colour, flavour and water soluble vitamins are lost)
6
Q
What are some examples of food that uses boiling?
A
- meat
- potatoes
- rice
- pasta
- veg
7
Q
What is steaming?
A
- cooking food with steam from boiling water or stock
- no fat is added because their is no direct contact with water
- gentle method
8
Q
What are some examples of food that you can steam?
A
- fish
- rice
- vegetables
9
Q
What is blanching?
A
- involves part cooking food is boiling water for a short time before putting it in cold/iced water
- cold water stops cooking process (helps preserve colour, texture and vitamins)
- removes harsh flavours in foods
10
Q
What are some examples of food that needs blanching?
A
- onions
- prepare fruit and veg for freezing
- tomatoes and almonds makes skins shrivel up, making the skins much easier to remove
11
Q
What is simmering?
A
- like boiling but more gentle as the temperature is slightly lower than boiling point
- mainly for soups and curries
- preserves more nutrients than boiling
12
Q
What is poaching?
A
- involves cooking food in a pan of liquid below boiling point (around 80 degrees)
- gentle and keeps food tender
13
Q
What type of food involves poaching?
A
- eggs
- fruit
- fish
14
Q
What is braising?
A
- slowly cooking food in an ovenproof pot than has the lid on and contains liquid, and often herbs and vegetables
- mixture of steaming and simmering
- great for big or tough joints of meats, gentle cooking of meat helps tenderise it
15
Q
What is stir- frying?
A
- done in a wok coated in a small amount of oil, making it quite healthy
- noodles, vegetables, tofu and small pieces of meat and fish
- cooks very quickly and moved around the wok all the time
16
Q
What is shallow frying?
A
- uses a frying pan coated in a medium amount of fat or oil
- meat (bacon and sausages), fish, eggs, pancakes
- more fat is used so less healthy
- gives a crispier texture
17
Q
What is sweating?
A
- releases moisture from food making it more tender and sweet tasting
- vegetables like onions, small amount of oil on low heat
- hot air rises (top of of oven is hotter than bottom)
18
Q
What is baking?
A
- uses dry heat, usually in an oven
19
Q
What type of foods can be baked?
A
- bread
- pastries
- potatoes
- meats
20
Q
Why are modern electric ovens more useful?
A
- fan assisted
- food bakes more evenly because all parts of the oven are at a similar temperature
- oven heats up quicker and your food cooks quicker so they use less energy
21
Q
What is grilling?
A
- uses dry heat at a higher temperature than baking or roasting to cook food
- as food is grilled fat drips out of the food and the outside of the food becomes golden and crisp
- smaller bits of meat like steak and sausages, vegetables and cheeses like halloumi
22
Q
What are the advantages of grilling?
A
- foods quickly at a high temperature
- fairly healthy as no fat is added and fat from the food drips off when cooked
- grilling on a bbq gives food a smoky flavour
23
Q
What are the disadvantages of grilling?
A
- high heat makes it hard to cook food evenly
- easier to burn the food
- handling raw and cooked meats on a bbq may lead to cross contamination
24
Q
What is roasting?
A
- roasting uses dry heat from an oven
- done at a higher temperature than baking
- fat is added to the outside of the food
25
Q
What are examples of foods that have need roasting?
A
- large cuts of meat
- potatoes
- vegetables
26
Q
What are the advantages if roasting?
A
- extra fat and high temperature helps to brown and crisp the outside of the food
- fat from roasted meat can be used to cook other food (potatoes)
- can produce meat with an undercooked centre which people like
27
Q
What are the disadvantages of roasting?
A
- isnt always healthy as extra fat is often added
- takes a long time to roast food, uses a lot of energy
28
Q
What is dry frying?
A
- cooking food in a pan without fat or oil
- dry fry foods that contain natural fat (minced meat or bacon)
- nuts, seeds, spices
- uses a medium heat
29
Q
What are the advantages of dry frying?
A
- no extra fats or oils added making it more healthy
- gives a distinct aroma to nuts, seeds and spices
30
Q
What are the disadvantages of dry frying?
A
- takes longer than other frying methods to cook meat thoroughly because lower temps needed at the start
- only be used for a small range of foods
31
Q
What is aeration?
A
- when fats such as butter and beaten with sugar (creaming) air becomes trapped in the mixture
- air makes the mixture fluffier and lighter in colour
- aeration gives cakes and spongey and light texture when cooked
32
Q
What are the different ways foods can be aerated?
A
- whisking egg whites with a whisk
- quickly beating ingredients with a spoon
33
Q
What is shortening?
A
- rub fat into flour, cover flour particles with fat (gives flour particles a waterproof coating)
- coating prevents long gluten molecules forming when water is added to the flour
- dough cannot become stretchy and naked goods like shortbreads keep a short firm and crumbly texture
- also used when making filled pies and tarts
34
Q
What is plasticity?
A
- fats have plasticity as were able to spread and manipulate them
- possible because fats contain a mixture of triglycerides (melt over different temperatures, so fats gradually soften over a range of temperatures rather than just melting at just one)
- more plasticity=more easier to spread
35
Q
When is plasticity most useful?
A
- decorating cakes with buttercream
- rubbing fat into flour to make shortened dough
- spreadable butter on sandwiches and toast
- putting cream cheese on crackers
36
Q
What are emulsions?
A
- formed when oily watery liquids are shaken together
- milk, margarine and mayo are all examples of emulsions
37
Q
What are the two ends in an emulsifier?
A
- hydrophilic (attracted to water)
- hydrophobic (repulsed by water)
38
Q
What happens when you add an emulsifier?
A
- 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
39
Q
What is an example of an emulsion?
A
- mayonnaise is a stable emulsion of egg yolk, oil and vinegar
- when making stable emulsions you need to ensure you add the oil or eater gradually and that you mix the ingredients for long enough
- hollandaise sauce (made from butter, water, egg yolks)
40
Q
What are the steps to make a hollandaise sauce?
A
- melt the butter in a pan
- mix the egg yolks and lemon juice in a bowl
- gently warm this mixture by placing the bowl over a pan of simmering water
- slowly add the melted butter to the mixture, constantly whisking
- keep whisking the sauce until its all mixed up together smoothly
41
Q
What is an example of a chemical raising agent used to produce carbon dioxide?
A
- when its heated bicarbonate of soda breaks down to produce carbon dioxide bubbles that expand to make the mixture rise
- unpleasant alkaline taste, used with a strong flavour (gingerbread)
- baking power is a mixture of bicarbonate of soda and cream or tarter (neutralisation reaction takes place when baking powder is heated which gets rid of the soapy taste)
- self raising flour = mixture of plain flour and baking powder
42
Q
What is an example of a biological raising agent to produce carbon dioxide?
A
- yeast is used a biological raising agent used in bread dough
- microorganism that causes fermentation (process of releasing alcohol and carbon dioxide)
- doughs containing yeast and proved (when carbon dioxide is released and trapped in the dough, causing it to rise- fermentation stops during baking as yeast is killed by the heat)
- dough is baked carbon dioxide expands causing the bread to rise even more
43
Q
How is steam used as a raising agent?
A
- hot oven to cook a mixture that contains a lot of liquid - water leaves the mixture as steam - as steam rises it raises the mixture up
- as the water leaves the food bakes and become more solid
44
Q
What is a mechanical raising agent?
A
- add air to mixtures with elbow grease
air can be folded into mixtures and doughs by:
- to fold a cake mixture, you carefully use a spoon or spatula to repeatedly pour the liquid mixture over itself (trapping air each time)
- pastry doughs can be folded into layers trapping air in between the layers each time you fold
- beating - spoon or fork to mix ingredients
- whisking
45
Q
What happens to proteins as food is cooked?
A
- denature
- chemical bonds holding their structure together break down
46
Q
How can proteins be denatured?
A
- physical agitation (whisking, beating)
- changes in temperature
- acids (lemon juice and marinades)
47
Q
What happens after proteins have been denatued?
A
- protein molecules collide with other protein molecules and coagulate
- water becomes trapped between the protein molecules
- coagulation also changes the appearance and texture of the food
48
Q
How are foams formed when air is trapped?
A
- foams (e.g chocolate mousse, whipped cream) form when gas becomes trapped (aeration) inside liquid
- when liquids containing proteins are agitated the proteins inside the liquid denature - causing them to stretch and air becomes trapped in the liquid
- when proteins coagulate air becomes trapped creating a foam
- over whisking causes these new protein bonds to break as air escapes and the foam collapses
49
Q
How does gluten allow doughs to stretch and rise?
A
- gluten is a protein found in wheat flour
- formed when water is mixed with the flour to make a dough and can be found in foods like bread, pasta, cakes and pastries
- molecules of gluten are coiled (stretch and bend giving doughs elasticity)
- doughs need to be kneaded to work the gluten , causing the strands to get longer, stronger and stretchier
- when it reaches a high temp, gluten coagulates and the dough stays stretched
50
Q
How does starch gelatinisation thicken liquids?
A
- gelatinisation helps to thicken foods that contain starch (sauces, custards and gravies)
- starch granules are mixed with the liquid- become suspended in it (if you don’t stir the liquid the granules sink to the bottom)
- granules are heated with water, bonds between starch molecules start to break allowing water molecules to enter - water is absorbed and starch granules swell in size and soften
- between 62 degrees and 80 degrees starch granules burst open and release their starch into the liquid
51
Q
How does dextrinization occur when starch is exposed to dry heat?
A
- starchy foods like bread or biscuits are cooked with dry heat
- starch molecules in the food break down smaller molecules called dextrin’s
- breakdown is called dextrinization and it gives food a browner colour and crispier texture
- longer the food is cooked the more starch is converted into dextrin
52
Q
How does sugar caramelise when its heated?
A
- sugar molecules break down when they reach a high temperature - causing sugar to turn brown and change flavour (caramelisation)
- can burn very quickly
53
Q
How can you avoid caramelised sugar burning?
A
- water is added during the early stage of heating
54
Q
What are the three steps sugar goes through as it caramelises?
A
- liquid is runny and has a sweet taste
- time passes it become more like a smooth caramel
- it turns harder and as it cools it becomes more like a candy
