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

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 

Chilling methods (Part 1)

1. Refrigerator system

Refrigeration is essential for the production, storage and distribution of chilled foods. The benefit of chilled storage is the extension of shelf life of the food product in good condition by slowing down the rate of deterioration. What must be emphasised for chilling is that it cannot improve the quality of a good product and it can only slow down the processes of spoilage but not stop the processes.

The video below shows how the refrigerator at your house works.

There are many factors that influence the rate at which the heat is extracted out from food product during chilling such as:

• The size and shape of the pack and container (affect the rate of heat transfer to the cooling air)
• The temperature and speed of the air
• Weight
• Density
• Water content
• Specific heat capacity
• Thermal conductivity
• Latent heat content
• Initial food temperature