Freezing

Question 1

What is the most satisfactory method for long term food preservation?

Answer 1

Freezing

Question 2

What is the temperature bracket that food being frozen at low-temperature levels uses?

Answer 2

18-30 degrees celsius

Question 3

Why does freezing work so effectively at preserving food?

Answer 3

Because it removes free water that is required for microbial growth

Question 4

How does freezing affect food quality?

Answer 4

Minimal nutritional impact, longterm freezing can impact the quality

Question 5

If freezing is so expensive, why do companies use this process for foods?

Answer 5

To maintain shelf-life and decrease spoilage.

Question 6

What must happen to uncooked produce to maximize food quality?

Answer 6

They must be blanched prior to freezing.

Question 7

Describe the freezing curve.

Answer 7

The plot of temperature vs. time

Question 8

What are the 3 distinct stages of freezing?

Answer 8

1. Removal of sensible heat until freezing temperature
2. Removal of latent heat leading to the formation of ice
3. Further removal of sensible heat for storage

Question 9

Why must produce cool pst 0 degrees?

Answer 9

For crystal formation

Question 10

How come crystal formation causes an increase in temperature?

Answer 10

Because there is energy being released to form the crystals

Question 11

How can one decrease the temperature for freezing?

Answer 11

By adding a solute such as salt.

Question 12

How does salt decrease the freezing temperature?

Answer 12

Because as the ice is forming the rest of the concentration is being taken up by salt to the freezing point must go down.

Question 13

Is there a clear freezing point for foods?

Answer 13

No, there is a range

Question 14

What is the freezing point defined as?

Answer 14

The highest temperature at which ice crystals will form.

Question 15

How does the rate of freezing impact crystal growth?

Answer 15

Slower freezing leads to a limited amount of ice crystals which grow to be quite large.

Question 16

How does rapid freezing effect foods?

Answer 16

There is a higher number of smaller ice crystals. This maintains cell rigidity and minimizes loss of water.

Question 17

Why might the quality of frozen foods go down slowly?

Answer 17

Because of the denaturation of muscle proteins as the unforzen region becomes concentrated with enzymes, proteins denature and affect the function.

Question 18

How can protein denaturation be prevented?

Answer 18

Rapid freezing so the ice crystal formation zone passes quickly

Question 19

What is the ice crystal formation zone?

Answer 19

0-5 degrees

Question 20

What factors effect rate of freezing? (5)

Answer 20

1. temperature difference between food and cooling medium
2. Heat transfer rate of cooling medium
3. Surface area of food
4. Product thickness
5. Agitation of product (mixing)

Question 21

What is the concern with a freezer which fluctuates in temperature?

Answer 21

Upon refreezing the ice crystal size increases and disrupts cell walls losing texture.

Question 22

What may cause freezer burn?

Answer 22

A decrease in humidity may lead to sublimation (solid to gas) of ice. this discolours food and denature protein. Texture is lost and rancidity develops.

Question 23

What should relative temperature humidity be kept at and why?

Answer 23

90% to reduce air movement across food products.

Question 24

What is glazing and how does it protect food?

Answer 24

The formation of a layer of water prior to freezing protects food from moisture loss.

Question 25

Why is food packaging useful when freezing food?

Answer 25

To prevent freezer burn and oxidation.

Question 26

How can freezing equipment be classified?

Answer 26

By type of heat transfer system used and whether or not it is direct/indirect contact cooling.

Question 27

Describe an air-blast and tunnel freezer.

Answer 27

freeze animal carcasses

Question 28

Describe a belt freezer

Answer 28

Provides uniform freezing, very controlled process

Question 29

Describe a fluidized bed freezer

Answer 29

The dancing one

Question 30

Describe the contact freezer

Answer 30

who knows

Question 31

Describe the scraped-surface freezer

Answer 31

Food is surrounded by a cold surface, this is widely used fro ice cream manufacturing.

Question 32

Describe cryogenic freezing

Answer 32

Cooling rapidly with liquid nitrogen

Question 33

Describe individual quick freezing

Answer 33

Food are frozen rapidly and individually for ease of consumer use. This is mostly used for frozen fruit. Dehydration is a concern so water is sprayed before freezing.

Question 34

Are nutrients lost during freezing in vegetables?

Answer 34

A small amount are when blanching and freezing.

Question 35

What nutrients are lost in fruits during freezing?

Answer 35

Vit. C, vitamin losses in the syrup upon thawing (unless you consume it).

Question 36

How is iced wine made?

Answer 36

Made from grapes that have been left to freeze naturally on the vine and are harvested below -8 degrees and crushed. It is much sweeter than regular wine but the high sugar content makes it difficult to ferment.