Chilling and Freezing: June 2015

Thursday, June 11, 2015

Chilling

Freezing

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

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

Wednesday, June 10, 2015

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.

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

Monday, June 8, 2015

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)

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

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