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4) Food Processing > Lecture 11: Commercial Freezing Methods and Equipment > Flashcards

Lecture 11: Commercial Freezing Methods and Equipment Flashcards

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1
Q

what is the goal of freezing methods?

A

to achieve rapid freezing

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2
Q

what are ways to achieve rapid freezing?

A
  1. use a medium with high h
  2. use a rapidly moving med
  3. use very low temp
  4. use thin profiles
  5. agitate particles
  6. use cryogenic conditions
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3
Q

what are factors that are helpful for achieving rapid freezing?

A

high h
large delta T
large A
low d

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4
Q

what are the two types of freezing, in terms of contact?

A

indirect and direct

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5
Q

what are 4 types of freezing methods? are they direct or indirecT?

A
  1. air freezing (direct)
  2. plate freezing (indirect)
  3. liquid immersion (direct)
  4. cyrogenic freezing (direct)
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6
Q

describe the air freezing method

A
  • most simple
  • direct contact of cooling medium with product and package
  • air temp: -18C to -40C
  • natural circulation or forced circulation air
  • room or tunnel
  • batch or continuous
  • mechnical refrigeration or cyrogenics
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7
Q

what is freezer burn? what is it caused by?

A
  • dessication/dehydration that causes discoloration and texture change
  • problem during frozen storage
  • especially for larger samples (eg. meat carcass) and un-packaged products
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8
Q

what is glazing?

A
  • coating of ice on surface of frozen food
  • prevents moisture loss from product
  • mostly done during frozen storage of the product rather than during freezing
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9
Q

what is sharp freezing?

A
  • slow and still air –> very slow freezing
  • not a common method used today
  • discovered in 1920’s by Lloyd Groff Copeman
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10
Q

what is air blast freezing? what benefits does it have?

A
  • forced air circulation with powerful fans

benefits:

  • high velocity increases turbulence of air so the heat transfer rate increases (large h)
  • conserves energy
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11
Q

what is tunnel freezing?

A
  • variation of air blasting freezing
  • tunnel insulated
  • has a conveyor through an air blast tunnel
  • product has a counter-current flow (co-current or bi-directional is also possible)
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12
Q

what is fluidized bed freezing?

how does the freezing rate compare to other methods?

what foods is this commonly used for?

A
  • version of air blast freezing
  • good for light weight products
    food is placed on a pourous bed. Powerful fans are used to force cold air to lift the product
  • much faster freezing rate
  • can be batch or continuous
  • used for peas, beans, carrot cubes, etc…
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13
Q

what is through flow freezing?

how does the freezing rate compare to other methods?

what foods is this commonly used for?

A
  • variation of fluidized bed system
  • also called packed bed freezing system
  • high air velocity, but insufficient to lift particles
  • fast freezing rates due to high air velocity and intimate contact
  • used for fish fillets and nuggets
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14
Q

what are the 5 techniques for air freezing?

A
  1. sharp freezing
  2. air blast freezing
  3. tunnel
  4. fluidized bed freezing
  5. through flow freezing
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15
Q

what is plate freezing?

what foods is it commonly used for?

A
  • packaged product is in indirect contact with cooling medium
  • good transfer rates due to good contact
  • contact plates are cooled by cold brine or refrigerant
  • temp: -30-50degC
  • common for sea fish freezing
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16
Q

what is liquid immersion freezing?

how does the cooling rate compare to the other methods?

how is heat transferred?

A
  • immersion of product into liquid media
  • intimate contact = provides fast and efficient cooling
  • heat transfer goes from liquid to solid and air to solid
17
Q

why is liquid immersion freezingnot common for non-packaged product?

A

due to residue concerns

18
Q

what does the freezing media in liquid immersion freezing consist of?

A 
propylene
glycol
glycerol
sodum chloride
calcium chloride
sugar syrup
19
Q

what is cyrogenic freezing?

A
  • very low temp
  • heat transfer from boiling of refrigerant
  • combined latent heat and sensible heat potential
  • direct contact between product and package
20
Q

describe cryogens used in cryogenic freezing

A

consists of liquid N2 and Co2

very low boiling/sublimintation temp

high latent heat

4) Food Processing (18 decks)

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