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Chilling

• Chilled Food
• Principles of chilling
• Effect of chilling
• Chilling methods (Part 1)
• Chilling Methods (Parts 2)
• Chilling Methods (Part 3)
• Chilled storage and retail display
• Transportation

Freezing

• Frozen Food
• Effect of freezing
• Freezing Methods
• Processing and Packaging

Chilling Methods (Part 3)

6. Ice

•  Use of ice / water mixture
• Effective heat transfer
• Process is a hydrocooling
• Chill product in bulk in short time
• Constant temperature

7. Vacuum

•  Used to solid product with large surface area to volume ratio
• Product is chilled in a vacuum chamber
• Heat is removed through evaporative cooling
• Rapid and economical
• Capital cost is high

8. Cryogenic

• Liquid nitrogen or solid carbon dioxide is used
• Heat is needed to boil the refrigerant 
• Cooling rate is high

Chilling Methods (Parts 2)

2. Moving Air

• versatility
• applicable to products of irregular shapes
• faster cooling as air speed increase

    2.1 Batch Air Cooler

    2.2 Continuous Air Cooler

• designed to produce even air velocity
• refrigeration capacity can be varied
• products are chilled through conveyer or continuous rack of trays
• cooled air is distributed either horizontally or vertically

    2.3 Wet air / bank cooling

• designed to overcome dehydration of product
• saturated wet cooled air
• more economical
• reduce weight loss
• great chilling efficiency
• large space is required for ice storage and operation

     

3. Direct contact

• heat transfer is based on direct of between product and metal surface

   3.1 Plate heat exchange

   3.2 Jacketed heat exchange

• cool the liquid in jacket vessel 
• cooling medium are circulated through the jacket of the vessel or through coil immersed in liquid
• vessel are provided with agitator to improve heat transfer
• low heat efficiency. Vacuum closed vessel reduce cooling time

4. Heat exchanger

   4.1 Belt heat exchanger

• effective for thin products
• continuous process
• easy cleaning
• reduce evaporation loss

   4.2 Continuous heat exchanger

5. Immersion / spray

• product are dipped into cold liquid
• high rate heat exchange
• reduce dehydratioon
• cool water or brine solution is used
• cold liquid can also be spray into food

Effect of freezing

Effect on microorganisms

• Microbial growth is stopped
• Kill spoilage microorganisms
• Kill 10% - 60% microbial in food

Effect on chemical changes and quality

• Colour loss (browning)
• Enzyme still active
• Slower rates of enzymatic & non-enzymatic reaction
• Fermentation activity decreases
• Acetaldehyde formation

Effect on physical changes and quality

• Affect the overall behavior of foods
• Free water frozen while bound water is unfreezable
• Formation of ice crystal in food
• Moisture loss (dehydration)

Freeze Burn

Frozen food require care for optimum quality. It is important to maintain the storage temperature and avoid any undesirable changes in food to occur.

Processing and Packaging

Pre-treatment

1. Blanching

• Immersion or steaming
• Providing good condition for freezing
• Improve eating quality
• Destruction of microorganisms
• Wilting vegetables
• Reduction of undesirable materials
• Inactivation of various enzymes
• Extension of shelf life

2. Heat treatment

• Low temperature long time
• Decrease cell damage and excessive softness
• Firmer texture

3. Dipping treatment

• Dipping / soaking in solution: brine, ascorbic acid, citric acid, sugar, etc
• Reduce browning
• Reduce enzymatic reaction
• Provide glazing that protect products from dehydration and oxidation

4. Bacterial 

ice nucleators

• Elevate nucleation temperature
• Reduce freezing time
• Increase freezing rate
• Improve quality

5. Antifreeze proteins (AFPs)

• Lower freezing temperature
• Bind to the ice crystal
• Retarding recrystallization

6. Osmotic concentration

• Soaking food items in concentrate solution such as sugar solution
• Partial removal of moisture from foods
• Improving product quality
• Reducing refrigeration load

7. Cryoprotection

• Protection of protein freeze denaturation
• Preserving functional properties of proteins
• Examples: Sorbitol, sucrose, polydextrose, maltodextrins
• Produce smooth textures in Surimi (crabstick)

8. Irradiation

• Treating with ionizing radiation generated by radioactive materials
• Retard spoilage microorganisms

Post-treatment

Thawing

• Essential to maximise quality retention
• Thawing through refrigerator, microwave oven, cooking
  

Chilled storage and retail display

Chilled storage

Control atmosphere storage rooms

• Design to store fruits such as apple

• Room is equipped with gas-tight seals

• Lower oxygen and high carbon dioxide and nitrogen

Retail display

1. Unwrapped products

    - forced-circulation cabinet

   - gravity cabinet

2. Wrapped products

   - multi - deck display cabinet (open)

 

   - multi - deck display cabinet (close)

Transportation

1. Overland transport

Different refrigeration system is used:

• mechanical
• eutectic plates
• liquid nitrogen (total-loss refrigerant)   

Various vehicle types

• small van
• long container trucks
• train 

2. Sea transport

• good refrigeration system allowed fresh products to be 
• transported up to 40 days
• meat products can be kept up to 23 weeks at -2°C with 
• correct packaging
• containers used can be insulated or refrigerated
• mainly for semi-process / process food
• bulky amount of product

3. Air transport 

• useful for highly perishable products such as fruit and vegetables
• mark-up and profit rule as deciding factors
• products are not refrigerated during transport
• insulated containers are used
• dry ice can also be used