This document discusses methods of chilling fish to preserve quality. It describes wet icing as the most common chilling method, where ice is placed in direct contact with fish to draw heat away. Other methods include ice slurries, refrigerated air, dry ice, and gel ice mats. Proper chilling ensures fish is kept at 0-4°C to slow spoilage. Mechanical refrigerators and cryogenic systems are chilling equipment that uses refrigerants like ammonia or carbon dioxide to draw heat from fish. Insulation materials like polystyrene and polyurethane are used in containers to slow heat transfer and maintain temperature. Chilling preserves quality with minimal nutritional or textural effects on fish.

1. 1
Y.Bavaneethan.
Lecturer
Department of Food Technology
SLGTI. SriLanka.
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2. INTRODUCTION
• Fish is highly perishable,
– proper handling must start from the moment it is
harvested until it reaches the consumer’s table.
– Lowering the temperature (chilling, refrigeration
and freezing) is the key factor in maintaining the
quality of fresh fish.
• Chilling is the most common practice in keeping the
freshness of fish.
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3. CHILLING
• Means the reduction of temperature to some
point below (-2 to -40C for superchilling) or
above (between 0 to 50C) the freezing point of
water in the fish muscles.
• Chilling does not stop spoilage but slows it
down considerably.
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4. METHODS OF CHILLING
• 1. WET ICE (ICING)
- Icing is most common and useful way of
chilling the fish catch.
- Cooling is effected by the direct contact
between the melted ice and the fish.
- When ice is placed in close contact with the
fish;
- heat transferred from the warm fish to the ice
resulting to the melting of ice; in turn the fish is
cooled down by the melted ice.
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5. WET ICE (ICING)
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6. The following considerations must be taken
when icing fish:
1. Sufficient ice must be used to maintain fish
temperature at 00C.
– For long term preservation more ice than fish is needed,
atleast usual 1:1 ice: fish ratio.
2. The arrangement of ice and fish must be in such a
way that accumulated water, blood and slimes can be
drained easily.
3. Ice and fish should be placed alternately to avoid
localized heating. Fish must be sufficiently
surrounded with ice on sides, top and bottom.
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7. 4. When packing mixed fish, big fish must be placed at
the bottom and small fish on top.
– Fish with delicate skin should be packed on top
of fish with scales.
5. Gutted fish must be filled up with ice in the belly
cavity,
– must be arranged with belly down in a slanting
position inside the container.
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8. • 2. Chilled by Ice Slurry
- This is also termed as “Slush ice” which is a mixture
of seawater and crushed ice used for the chilling of
fish catch.
Advantages of CSW(Chilled Sea Water) over icing:
• CSW chills fish much faster than wet ice.
• Fish in CSW do not suffer from physical damage due
to crushing or pressure from other fish.
• Fish in CSW are washed in the slurry.
• CSW chilled fish do not necessarily keep longer than
wet iced fish.
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9. ICE SLURRY
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10. Other Methods
3.Refrigerated Air
• Air chilling is commonly employed in big commercial
production. Chilled air is circulated by a finned
evaporator and fan situated at one end of the fish
room.
• These units are often referred to as air blowers.
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11. Outdoor Air Cooled Process
Chilling Refrigeration Models
( APS )
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12. Refrigerated Air at refrigerator box
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13. 4. Dry Ice
• Dry ice is solid carbon dioxide. Cooling is effected by the
evaporation of the dry ice.
• Due to its very low temperature (-78.90C), dry ice should
not be used in direct contact with fish to avoid cold burns.
COLD BURN
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14. • This method of chilling is preferred for air shipment of
fish, as this does not caused leakage.
• The use of dry ice is subject to restrictions because it
expands from a solid form into a gas and it may expel
oxygen, posing a hazard to the safety of airplanes
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15. 5. Gel Ice Mat
• Gel ice made by freezing a water-based gel.
The advantage of gel ice is that all water is
bound with no chance of water leakage during
thawing . Gel mat chilling is suitable for air
transport of fish.
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16. Chilling Equipments
• Chilling equipment is classified by the method
used to remove heat, into:
– mechanical refrigerators
– cryogenic systems.
• Batch or continuous operation is possible with
both types of equipment.
1. Mechanical refrigerators
• Mechanical refrigerators have four basic
elements:
– evaporator, compressor, condenser and expansion
valve.
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18. • The refrigerator material (Copper) should have:
– low thermal conductivity
– high rates of heat transfer
– high thermal efficiencies
• Refrigerant circulates between the four elements of the
refrigerator.
1. liquid refrigerant evaporates under reduced pressure, and
absorbs latent heat of vaporization and cools the
medium(food).
2. Refrigerant vapour passes from the evaporator to the
compressor where the pressure is increased.
3. The vapour then passes to the condenser where the high
pressure is maintained and the vapour is condensed.
4. The liquid passes through the expansion valve where the
pressure is reduced to restart the refrigeration cycle.12/4/2017 Y.BAVANEETHAN 18

19. – low boiling point and high latent heat of vaporization
– dense vapour to reduce the size of the compressor
– low toxicity and non-flammable
– low miscibility with oil in the compressor
– low cost
• Ammonia has excellent heat transfer properties and is
not miscible with oil,
– but it is toxic and flammable, and causes corrosion
of copper pipes.
• Carbon dioxide is nonflammable and non-toxic,
making it safer,
– but it requires considerably higher operating
pressures compared to ammonia.
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•The important properties of refrigerants are as follows:

20. • CFCs are all non-toxic and non-flammable and have
good heat transfer properties and lower costs than other
refrigerants.
– but, their interaction with ozone in the earth’s atmosphere.
• Now, ozone-friendly HCFCs(Partially halogenated CFC)
are being developed and are likely to become important
refrigerants.
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21. Cryogenic chilling
• A cryogen is a refrigerant that changes phase by
absorbing latent heat to cool the food.
• Cryogenic chillers use solid carbon dioxide, liquid
carbon dioxide or liquid nitrogen.
• Solid carbon dioxide removes latent heat of
sublimation.
• The advantages of carbon dioxide include:
– higher boiling and sublimation point than nitrogen,
and therefore a less severe effect on the food
– most heat capacity arises from the conversion of
solid or liquid to gas.
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22. • Solid carbon dioxide can be used in the form of ‘dry-
ice’ pellets, or
– liquid carbon dioxide can be injected into air to
produce fine particles of solid carbon dioxide -
‘snow’.
– which rapidly sublime to gas.
• Older meat processing, dry-ice pellets layered with
minced meat and filled into containers.
– However, lack of uniformity distribution of pellets.
– Result, some meat becoming frozen and some
remaining above 5ºC
– Which permitted bacterial growth.
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23. • More recently the use of snow horns (Dry Ice Snow),
– To distribute a fine layer of snow over minced
meat.
– It is eliminated above problems and resulted in
rapid uniform cooling to 3–4 OC.
• Applications of cryogenic cooling include sausage
manufacture,
– where carbon dioxide snow removes the heat
generated during size reduction and mixing
– And cryogenic grinding where the cryogen reduces
dust levels, prevents dust explosions.
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24. Types of Insulation
• The primary aim of using insulation in containers is
to slow down the rate of heat exchange between two
bodies at different temperatures.
• The efficiency of an insulating material in
preventing heat flow is measured as thermal
conductivity (k).
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25. 1. Cork and Fiberglass Mat
• Cork and fiberglass mats have k values of 0.04 and
0.03, respectively. They are good insulating
materials, however, they are highly permeable to
water vapor.
CORK FIBERGLASS MAT COMPOSITED WITH
ALUMINUM FOIL
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26. 2. Rice Hull, Kapok, Coconut fibers and sawdust
• These materials are cheap but not water-resistant.
Kapok when compressed loses its insulating power .
RICE HULL
Kapok fiber
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27. 3. Polystyrene (styrophore)
 It is widely used as an insulating material because it
is easy to produce.
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28. 4. Polyurethane
• Expanded polyurethane has almost similar
properties (except for its lower compressibility
strength) as that of expanded polystyrene.
• Polyurethane material can be foamed in situ on to
the surface that needs to be insulated.
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29. Effect on foods
• Chilling foods to correct storage temperature causes
little or no reduction of eating quality or nutritional
properties.
• Most significant effect of chilling,
– Foods is hardening due to solidification of fats and
oils.
• Lipid oxidation is one of the main causes of quality loss
in cook–chilled products,
– Cooked meats rapidly developed oxidised flavour
termed ‘warmed-over flavour’.
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30. • Quality deterioration:
– Evaporation of moisture from unpackaged chilled
meats and cheeses.
– Rapid staling of sandwich bread at reduced
temperatures and moisture migration from sandwich
fillings.
• In cook–chill systems, nutritional losses are,
– insignificant for thiamine, riboflavin and retinol.
– but vitamin C losses are 3.3–16% day1 at 2ºC.
• Vitamin C losses in cook–pasteurize–chill procedures are
lower than cooked–chilled foods.
– Spinach lost 66% within 3 days at 2–3ºC after cook–
chilling compared with 26% loss within 7 days at 24ºC
after cook–pasteurizing–chilling.
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