Freezing

Question 1

why is super cooling needed?

Answer 1

ice crystals don’t form at exactly 0 degrees; need super cooling to arrange in lattice structure

Question 2

freezing refers to storage of food between ___ and __ degrees C

Answer 2

-18; -30

Question 3

3 stages of freezing curve?

Answer 3

removal of sensible heat (liquid), removal of latent heat (liquid and solid), removal of more sensible heat (solid)

Question 4

why is there continual decline in freezing point for food materials?

Answer 4

presence of solute depresses freezing point–>pure water freezes out, unfrozen region gets very concentrated, FP v even more

Question 5

what is freezing range?

Answer 5

between 0 and -5 degrees C

Question 6

slow freezing leads to formation of ___ number of ___ ice crystals

Answer 6

small; large

Question 7

effects of slow freezing?

Answer 7

1) damage cell structure, loss of structural integrity 2) pull water out of cell due to osmosis (cell dehydration)
3) cells can’t maintain rigidity when thawed

Question 8

why is disruptive effect of size of ice crystals minimal in MFP?

Answer 8

elasticity of cell structure in muscles

Question 9

why is there still some quality loss in muscle food when frozen?

Answer 9

denaturation of muscle proteins because during freezing, unfrozen region become [ ] with enzyme and acids which denature proteins

Question 10

rate of freezing influenced by:

Answer 10

temp differential, heat transfer rate, SA of food, product thickness, agitation of liquid

Question 11

commercial freezers at ___C, domestic at ___C

Answer 11

-25; -18

Question 12

what happens to ice crystals when re-freeze?

Answer 12

size increases

Question 13

decrease in humidity in freezer leads to ______ on food surface

Answer 13

sublimation of ice (freezer burn)

Question 14

what is sublimation?

Answer 14

ice–>vapour (solid–>gas)

Question 15

relative humidity inside freezer should be kept above ___%

Answer 15

90

Question 16

food is ____ prior to freezing

Answer 16

glazed

Question 17

what is glazing?

Answer 17

formation of water layer on food surface that turns into ice coat, protects food from moisture loss

Question 18

types of heat transfer systems:

Answer 18

air cooling, plate cooling, cryogenic cooling (can be direct or indirect)

Question 19

types of freezers

Answer 19

air-blast, tunnel, belt, fluidized bed, contact, scraped surface, cryogenic

Question 20

freezer used for ice cream manufacture

Answer 20

scraped surface

Question 21

cryogenic freezing uses liquid ___ or ___

Answer 21

nitrogen (-196C); ammonia (-33)

Question 22

what is IQF?

Answer 22

Individual Quick Freezing

Question 23

IQF used for:

Answer 23

frozen fruit processing

Question 24

why do frozen concentrated juices exhibit low Vit C loss?

Answer 24

low pH, low O2, low water activity

Question 25

how is ice wine made?

Answer 25

grapes left freeze naturally on vine, harvest below -8C and crushed, press frozen grapes to yield [ ] juice very sweet

Question 26

why is juice in ice wine difficult ferment by yeast?

Answer 26

high sugar content

Question 27

This is defined as the highest temp at which stable ice crystals appear

Answer 27

freezing point