food science

Question 1

why do we cook food to make it safe for us?

Answer 1

1. many food sources can contain harmful bacteria that can make us ill , it can be killed if food is cooked long enough at a high temp
2. some foods contain harmful toxins destroyed when food is cooked, e.g. red kidney beans have to be soaked, boiled and simmered before being safe to eat

Question 2

why do we cook food to improve shelf life?

Answer 2

1. when foods are cooked at high temps, bacteria and mould destroyed
2. one way food preserved during manufacturing process
3. e.g. milk is pasteurised, helps it stay fresh for longer

Question 3

why do we cook food to develop flavours?

Answer 3

1. chemical reactions take place during cooking that changes flavour of food e.g. caramelisation
2. roasting meats and veg creates more intense flavours food becomes browner and crispier with more fat added as water evaporates from iknside of food
3. also flavours of different foods combine

Question 4

why do we cook foods to improve texture?

Answer 4

1. cooking usually makes it easier for us to chew, swallow and digest food
2. some foods softer when cooked, e.g. rice and pasta swell as starch molecules soften
3. meats become more tender as solid fats in food melt and protein softens
4. other foods become firm when cooked e.g. proteins in egg whites coagulate turns food opaque and more solid
5. meats tough and egg whites rubbery if over cooked
6. change in texture makes food more pleasant to eat

Question 5

why do we cook food to give variety in the diet?

Answer 5

1. foods cooked in different ways to create variety
2. e.g. beef= grilled steak, roast beef, beef stew, pan-fried minced beef or barbequed burger

Question 6

what is conduction?

Answer 6

1. the transfer of heat energy through the vibration of particles
2. in solid particles held closely together, when when particle vibrates it vibrates those around it and passes on the vibration
3. when pan on hob, heat energy from hob causes particles in the pan to vibrate more and gain heat energy
4. when particles collide with others pass some extra heat energy onto them
5. this process continues throughout pan till heat passed all the way through
6. when food placed into hot pan, heat energy transferred from particles in the pan to particles in food in similar way till food cooked all the way through
7. energy from cooker quickly transferred to pan and contents when using metal pan as its good conductor of heat

Question 7

what is convection?

Answer 7

1. transfer of heat energy through gasses and liquids
2. when you heat a liquid the liquid near the heat source warms faster
3. warmer liquid rises above colder surroundings
4. as warm liquid rises, cold liquid takes its place
5. as this process continues, you end up with a circulation of fluid (convection currents) - after a while, this circulation of heat results in whole fluid being heated
6. convection also occurs in ovens - hot air rises and cooler air falls

Question 8

what is radiation?

Answer 8

1. transfer of heat energy through waves of radiation
2. unlike conduction and convection , there is no direct contact between heat source and food
3. cookers like grills and toasters use radiation
4. they emit waves of radiation - when waves reach food they are absorbed and heat the food
5. microwaves use radiation to heat fat, sugar and water molecules in our food

Question 9

what is boiling?

Answer 9

-cooking food by heating in a pan of boiling liquid
-foods that are boiled include: meat, potatoes, rice, pasta and veg
-quite harsh cooking method cant be used on delicate food as bubbles would break up foods
-over-boiling can make foods like pasta too soft
-boiling is healthy cooking as no fat added, however if boiled too long colour, flavour and water soluble vitamins are lost in the water
-not as tasty and attractive as other cooking methods
-less energy with little water and lid han other cooking methods