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FDSC200 > Week12C1 > Flashcards

Week12C1 Flashcards

1
Q

Does freezing reduce the water activity of food?

A

Heating, freeze drying, freeze concentration, and osmotic concentration methods are used to reduce water activity of foods.

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2
Q

T or F : in home freezers there is a good circulation of air.

A

F

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3
Q

T or F : in commercial freezing the air is either still or moving

A

T

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4
Q

What is the common freezing method used in home refrigerator

A

Sharp/still freezing

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5
Q

What is the temperature of still air freezing

A

-23˚C to -30˚C

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6
Q

What is the kind of product mostly suited for the still air freezing

A

rate insensitive products

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7
Q

_____ uses high velocity air to speed the freezing rate

A

blast freezing

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8
Q

T or F : blast freezing is a continuous method

A

False, but it can be with specialized equipment

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9
Q

In the ____ method, product placed on trays or mesh belt and run counter current to high-velocity cold air - continuous process

A

tunnel freezer

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10
Q

What are the problems associated with the tunnel freezer method

A

maintaining control over product dehydration (freezer burn).

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11
Q

What is a freezer burn?

A

food injury due to the sublimation or evaporation of ice during freezing that leads to localized dehydration.

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12
Q

Which method is best suited for the flat-packed products

A

indirect contact plate freezer

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13
Q

Name the 7 freezing methods seen in class?

A
  1. Sharp / still air
  2. blast
  3. Tunnel
  4. Indirect contact plate freezer
  5. Scraped surface heat exchanger
  6. Immersion freezing
  7. Cryogenic freezing
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14
Q

T or F : in plate freezing, the cooling medium is air and it is in direct contact with the food

A

false, the contact is indirect

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15
Q

What is the exterior jacket or coolant used in the scraped surface heat exchanger

A

ethylene glycol

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16
Q

T or F : the scraped surface heat exchanger is a continuous method

A

true

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17
Q

What is the method in which the air is not the cooling medium

A

scraped surface heat exchanger
immersion freezing
cryogenic freezing

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18
Q

Name the continuous freezing methods seen in class

A 
blast freezer (can be)
tunnel freezing
scraped surface heat exchanger
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19
Q

Describe the immersion freezing

A

The packaged product are immersed in the refigerated medium such as ethylene glycol, sugar or salt solution.

20
Q

What is the method that is best suited for irregular shaped products?

A

Immersion freezing or cryogenics

21
Q

Which method is best suited for shrink wrapped turkey or chicken or fish

A

immersion freezing.

22
Q

Why do we use salt and sugar solution as the cooling medium

A

because they lower the freezing point

23
Q

What is the freezing point of ethylene glycol?

A

-67˚C

24
Q

What is the freezing point of liquid nitrogen and liquid CO2

A

nitro : -196˚C

CO2 : -79˚C

25
Q

What is the cooling medium in the case of cryogenic freezing

A

the cooling medium is the cryogenic liquid

26
Q

What is a cryogenic liquid?

A

a liquid with a boiling temperature that is under -180˚C

27
Q

How much heat is needed to be removed from products freezed with liquid nitrogen

A

386 kilojoules/kg of PRODUCT

28
Q

what is the latent heat of evaporation for the change od state from 195˚C to 196˚C in nitrogen?

A

200kj/kg OF PRODUCT

29
Q

Define temperature differential?

A

the difference in temperature from the food product and the cooling agent. IT is the temperature driving force in heat exchanger systems (freezing for example)

30
Q

What is the freezing point of carbon dioxide?

A

-79˚C and under

31
Q

What is the BP of carbon dioxide

A

-79˚C and over

32
Q

What is the BP of liquid nitrogen

A

-196˚C

33
Q

What is the freezing point of liquid nitrogen?

A

-196˚C

34
Q

T or F : the boiling point and freezing points of cryogenic liquids are nearly equal

A

true

35
Q

Why is dry CO2 considered a cryogenic liquid if its boiling point is 79˚C?

A

because it can absorb twice as much energy as liquid nitrogen, making up for the temperature differential.

36
Q

What is the temperature at which super freezers are operating?

A

-60˚C

37
Q

What are the different categories of processed foods preserved by reduced water activity?

A
  1. dehydrated
  2. concentrated
  3. intermidiate moisture
38
Q

T or F : concentration was one of the earliest preservation method used by man

A

false, it is drying, and it was originally based on solar energy.

39
Q

What is the the lowest moisture content that can be reached with the simple solar drying?

A

15%

40
Q

What are the disadvantages of solar drying?

A

15% reduced water content
uncontrolled (weather)
contamination

41
Q

What is the moisture content that can be reached with the food dehydration?

A

1-5%

42
Q

Name one challenge associated with the foods made by dehydration

A

the reconstitution of the food product.

43
Q

What is the key to efficient dehydration?

A

maximizing the heat/mass transfer

44
Q

what are the parameters affecting the dehydration?

A
  1. surface area
  2. product profile
  3. temperature differential
  4. RH (influenced by the medium)
45
Q

There is an ____ relationship between the surface area and the particle size

A

exponential

46
Q

T or F : hot air is capable of retaining more moisture and so is better for the mass transfer in the case of drying

A

true.

47
Q

What will happen if the RH of the food product and the air is the same

A

the food product will not loose moisture

FDSC200 (23 decks)

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