Cold Preservation and Processing

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Cold Preservationand Processing

• Chapter 9

2
Historical Perspective

• 1875 - first mechanical ammonia refrigeration
  system invented
• 1920s - Clarence Birdseye initiated frozen food
  packaging

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Storage Temperatures

• Cool storage 16 to -2oC (60 to 28oF)
• Refrigerators 4.5 to 7oC (40 to 45oF)
• Frozen storage 0 to -18oC (32 to 0oF)

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Microbial Growth

• Best above 10oC (50oF)
• Some growth at sub-freezing temps as long as
  water is available
• Little growth below -9.5oC (15 oF)

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RefrigeratedStorage
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Cool Storage Is

• Gentlest method of food preservation
• Few adverse effects on
• Taste
• Texture
• Nutritive value
• Color
• Short time preservation

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Timeliness of Refrigeration

• ASAP after harvest/slaughter
• Remove heat rapidly through use of
• Moving air
• Hydrocooling
• Vacuum cooling
• Liquid nitrogen

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Requirement ofRefrigerated Storage

• Low temperatures
• Air circulation
• Humidity control (80 to 95)
• Modified gas atmospheres

9
Factors AffectingCooling Requirements

• Cold storage room insulation
• Frequency of door opening
• Heat load of food product
• Quantity of hot product loaded daily
• Respiration rate of food product
• C6H12O66O2 Þ 6CO26H2Oheat

10
Controlled Atmosphere Storage

• Standard cold storage temperatures humidity
• Reduced O2 levels
• Elevated CO2 levels
• Why?

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C6H12O66O2 Þ6CO26H2Oheat
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Types of ControlledAtmosphere Storage

• Drive-in cold storage rooms
• Packaged
• Fruits
• Vegetables
• Meats
• Hypobaric (reduced pressure) storage
• Reduces air (and O2) availability

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Changes in Food During Refrigerated Storage

• Chill injury
• Flavor/odor absorption
• Loss of
• Firmness
• Color
• Flavor
• Sugar/acid

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FrozenStorage
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Initial Freezing Point

• Pure water freezes at 0oC (32oF)
• With dissolved salt, sugar or other components,
  water would freeze at
• higher temperatures?
• or
• lower temperatures?

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Initial Freezing Point

• Pure water freezes at 0oC (32oF)
• With dissolved salt, sugar or other components,
  water would freeze at
• higher temperatures?
• or
• lower temperatures?

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TRIVIA

• Why is salt added to ice in a ice cream freezer?
• How cold is ice when it begins to freeze?
• How cold will ice get?

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Freezing Curve
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Changes During Freezing

• Concentration effects
• precipitation, salting-out, dehydration
• Ice crystal damage
• cell rupture, emulsion disruption
• Slow freeze large ice crystals
• Want a rapid freeze to -18oC (0oF)

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Intermittent Thawing

• Increases ice crystal size
• Damaged cell very susceptible to enzymatic
  degradation

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Freezing Methods

• Freezing in air
• Still-air sharp freezer
• Blast freezer
• Fluidized-bed freezer

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Tunnel Freezer
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Freezing Methods

• Indirect contact freezing
• Single plate
• Double plate
• Pressure plate
• Slush freezer
• (In all cases, food or food packages are in
  direct contact with a surface that is cooled by a
  refrigerant)

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Freezing Methods

• Immersion freezing
• Heat exchange fluid
• Compressed gas
• Refrigerant spray
• Very fast freezing using liquid nitrogen
• IQF Individually Quick Frozen

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Liquid Nitrogen Spray Freezing Unit
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Packaging

• Protect against dehydration
• Strong flexible
• Protect against light air
• Liquid tight