food science

Question 1

define conduction

Answer 1

transfer of heat energy through the vibration of particles

Question 2

define convection

Answer 2

transfer of heat energy through gases or liquids

Question 3

define radiation

Answer 3

transfer of heat energy through waves of radiation

Question 4

why is boiling a healthy way to cook?

Answer 4

no fat is added

Question 5

how is heat transferred when boiling? (2)

Answer 5

• conduction from the pan to the liquid and through the food
• convection through the liquid

Question 6

how is heat transferred when steaming?

Answer 6

• conduction from pan to the water and through the food
• convection through the steam

Question 7

how is heat transferred when poaching?

Answer 7

• conduction from pan to the liquid and through the food
• convection through the liquid

Question 8

how is heat transferred when braising?

Answer 8

• conduction from dish to liquid and through the food
• convection through the liquid and steam

Question 9

how is heat transferred when frying?

Answer 9

conduction from pan to fat and through the food

Question 10

how is heat transferred in an oven?

Answer 10

radiation and convection and through food by conduction

Question 11

how is heat transferred when grilling?

Answer 11

radiation from grill/hot grills or conduction if using griddle pam

Question 12

how is heat transferred when dry frying?

Answer 12

conduction from cooker to pan and also through food

Question 13

define denature

Answer 13

chemical bonds holding their structure together break down

Question 14

how do proteins denature during preparation and cooking? (2)

Answer 14

1. proteins denature when cooked
2. proteins unravel and their shape changes

Question 15

3 ways proteins can denature

Answer 15

acid
change in temperature
physical agitation (whisking/beating)

Question 16

explain the process of coagulation (3)

Answer 16

• after proteins have denatured, protein molecules collide with other protein molecules and coagulate
• water becomes trapped between protein molecules
• coagulation also changes appearance + texture of food

Question 17

how are foams formed when air is trapped? (3)

Answer 17

• occurs when gas becomes trapped inside liquid
• when liquids containing protein are agitated the proteins inside the liquid denature causing them to stretch and air becomes trapped in the liquid
• when the proteins coagulate air becomes trapped creating a foam

Question 18

how does gluten allow dough to stretch and rise? (2)

Answer 18

• dough needs to be kneaded to work the gluten causing gluten strands to get longer and stretchier
• when it reaches a high temp., gluten coagulates and the dough stays stretched

Question 19

how does gelatinisation help thicken liquids? (6)

Answer 19

• starch granules are first mixed with a liquid they become suspended in it
• when the granules are heated with water the bonds between starch molecules start to break allowing water molecules to enter.
• As water is absorbed starch granules swell in size and soften
• at 62-80C starch granules burst open and release their starch into liquid
• this causes the liquid to thicken
• once cooled the liquid solidifies and a solid gel is formed

Question 20

how does dextrinisation occur when starch is exposed to dry heat? (2)

Answer 20

• when starchy foods are cooked with dry heat the starch molecules in the food break down into smaller molecules called dextrins
• this is called dextrinisation

Question 21

how does sugar caramelise when its heated?

Answer 21

sugar molecules break down when they reach a high temperature causing sugar to turn brown and change flavour

Question 22

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