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Food Science 210 > Freezing > Flashcards

Flashcards in Freezing Deck (27):
1

why is super cooling needed?

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

2

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

-18; -30

3

3 stages of freezing curve?

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

4

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

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

5

what is freezing range?

between 0 and -5 degrees C

6

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

small; large

7

effects of slow freezing?

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

8

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

elasticity of cell structure in muscles

9

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

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

10

rate of freezing influenced by:

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

11

commercial freezers at ___C, domestic at ___C

-25; -18

12

what happens to ice crystals when re-freeze?

size increases

13

decrease in humidity in freezer leads to ______ on food surface

sublimation of ice (freezer burn)

14

what is sublimation?

ice-->vapour (solid-->gas)

15

relative humidity inside freezer should be kept above ___%

90

16

food is ____ prior to freezing

glazed

17

what is glazing?

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

18

types of heat transfer systems:

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

19

types of freezers

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

20

freezer used for ice cream manufacture

scraped surface

21

cryogenic freezing uses liquid ___ or ___

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

22

what is IQF?

Individual Quick Freezing

23

IQF used for:

frozen fruit processing

24

why do frozen concentrated juices exhibit low Vit C loss?

low pH, low O2, low water activity

25

how is ice wine made?

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

26

why is juice in ice wine difficult ferment by yeast?

high sugar content

27

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

freezing point