food science

Question 1

what is convection

Answer 1

transfer of heat through liquids and gases

Question 2

equipment that cooks with radiation

Answer 2

grill, toaster, microwave

Question 3

how do microwaves heat food

Answer 3

radiation

• heat energy is transferred by waves of energy hitting food, water molecules absorb the waves which heats them up

Question 4

heat transfer in an oven

Answer 4

heating element emits radiation, hot air rises and pushes cool air down which creates a convection current, heat then transferred through food by conduction

Question 5

heat transfers in simmering sauce on a hob

Answer 5

to base of pan by conduction, pan heats sauce at base by conduction, heat transferred through the sauce by convection

Question 6

benefits of blanching

Answer 6

the cold water preserves colour, texture and vitamins

Question 7

why is food cooked

Answer 7

• to make it safe to eat - kills pathogenic bacteria and harmful toxins
• improves shelf life - bacteria and mould are destroyed
• develops flavour - chemical reactions change the flavour, cooking can allow different flavours to combine
• improves texture - easier to chew, swallow and digest
• gives variety in the diet

Question 8

poaching

Answer 8

cooking food in a pan of liquid below boiling point (usually around 80˚C)

food can be poached in a flavoured source to add variety and flavour
- if not, it can lose flavour to the liquid

Question 9

braising

Answer 9

slowly cooking food in an ovenproof pot with the lid on that contains liquid

• the food is cooked by both simmering and steaming
• helps tenderise big/tough joints of meat
• meat is usually fried to light brown to seal it before braising, helps keep juices in the meat and give a caramelised flavour
• flavours in the pot are absorbed by the meat

Question 10

pros and cons of baking

Answer 10

+ wide variety of foods
+ crisps and browns outside of the food, which tastes and looks nice
+ quite healthy bc no extra fat is added, and solid fats in the food often leave once baked

• can take a long time
• food can get dried out
• uses a lot of energy, the oven has to stay at a high temp for a long time

Question 11

pros and cons of grilling

Answer 11

+ food cooks quick at a high temp
+ no fat is added, so fairly healthy
+ fat drips out of the food and the outside becomes golden and crisp
+ grilling on the barbecue can give a popular, smoky flavour

• the high heat makes it difficult to cook evenly
• easy to burn the outside and have the inside still raw
• handling raw and cooked meat on a barbecue can lead to cross-contamination

Question 12

modern electric ovens

Answer 12

fan assisted/convection ovens

• circulate air
• the food bakes more evenly bc the oven is all at the same temperature
• use less energy - the oven heats quicker and the food cooks quicker

Question 13

roasting

Answer 13

+ extra fat and high temp - browns and crisps outside but keeps inside moist which is yum
+ fat from roasted meat can be used to cook other foods
+ tasty and moist
+ can produce a rare centre - which lots of people like

• extra fat is added - not super healthy
• takes a long time to cook, uses a lot of energy

Question 14

pros and cons of dry frying

Answer 14

+ no fats added - healthier
+ can give a more distinct aroma to nuts, seeds and spices

• takes longer - lower temps are needed at the start to melt fats
• can only be used for a small range of foods (should contain natural fat)

Question 15

proteins denaturing

Answer 15

when food is cooked proteins denature - the chemical bonds holding their structure together break down
it is usually irreversibe

they can denature in several ways:
• physical agitation (whisking, beating, kneading)
• temperature change (heat)
• acids

Question 16

protein coagulation

Answer 16

(post denaturing)

• protein molecules collide with other protein molecules and coagulate (join together)
• water gets trapped between the protein molecules
• coagulation changes the appearance and texture of food
• overcooking food - coagulation happens too much and the protein tightens, this forces water out of the molecules making it dry and chewy

Question 17

forming foams

Answer 17

• proteins inside the liquid denature from agitation
• they coagulate and form a foam
• over whisking causes the bonds to break - air escapes and the foam collapses
• some foams can form a solid structure when cooked

Question 18

gluten

Answer 18

gluten - a protein found in wheat flours

• forms when water is mixed with wheat flour to form a dough
• gluten molecules are coiled - they can stretch and bend which gives doughs elasticity
• kneading doughs works the gluten - causes gluten strands to get longer, stronger and stretchier
• at high temps, gluten coagulates and the dough stays stretched - gives food like bread a well-risen, airy texture

Question 19

gelatinisation

Answer 19

• when starch granules are first mixed with a liquid they become suspended - without stirring they will sink to the bottom
• heating the granules with water - bonds between starch molecules begin breaking, allowing water to enter. water is absorbed so starch granules swell and soften
• between 62˚C and 80˚C the granules burst open, releasing their starch into the liquid, causing the liquid to thicken
• when it cools, the liquid solidifies and a solid gel is formed

Question 20

dextrinisation

Answer 20

when starchy foods are cooked with dry heat

• the starch molecules break down into dextrins

Question 21

caramelisation

Answer 21

sugar molecules break down at high temps causing the sugar to turn brown and change flavour

1) runny and sweet
2) more like a smooth caramel
3) becomes harder and more like a candy as it cools

Question 22

shortening

Answer 22

• flour particles are coated in fat, giving them a waterproof coating
• the coating prevents long gluten molecules forming when water is added

some fats are called shortening when they have 100% fat content (no water), stopping gluten formation and preventing steam from raising the food

Question 23

plasticity of fats

Answer 23

• fats contain a mixture of different triglycerides which melt any different temperatures - so they soften over a range of temps vs melting at one
• easy to spread - made of a mixture of triglycerides with low melting points
• the more unsaturated fatty acids that a fat/oil contains, the more plasticity that it’ll have

Question 24

emulsifiers

Answer 24

emulsions are formed when oily and watery liquids are shaken together but won’t become stable without an emulsifier

• molecules in an emulsifier have a hydrophilic and hydrophobic end

emulsions can be oil-in-water (milk, mayonnaise, dressings)
or water-in-oil (margarine, butter)

Question 25

chemical raising agent

Answer 25

bicarbonate of soda

• breaks down to form CO2 bubbles when heated, these expand to make the mixture rise
• alkaline taste, needs to be used with a strong flavour to mask it (chocolate cake)

baking powder = a mix of bicarbonate of soda and cream of tartar,
• a neutralisation reaction takes place when baking powder is heated so it doesn’t taste weird

self-raising flours - contain a mix of plain flour and baking powder

Question 26

biological raising agent

Answer 26

yeast

• it’s a microorganism that causes fermentation - releasing CO2 and alcohol
• doughs with yeast are often proved to allow fermentation
• fermentation stops during baking as the yeast is killed by the heat
• the CO2 expands during baking, causing further rise

Question 27

mechanical raising agents

Answer 27

folding cake mixture
folding pastry doughs
beating
sieving 
creaming