2. INTRODUCTION
โข Fish is highly perishable,
โ proper handling must start from the moment it is
harvested until it reaches the consumerโs table.
โ Lowering the temperature (chilling, refrigeration
and freezing) is the key factor in maintaining the
quality of fresh fish.
โข Chilling is the most common practice in keeping the
freshness of fish.
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3. CHILLING
โข 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.
โข Chilling does not stop spoilage but slows it
down considerably.
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4. METHODS OF CHILLING
โข 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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6. The following considerations must be taken
when icing fish:
1. Sufficient ice must be used to maintain fish
temperature at 00C.
โ 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.
โ 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,
โ must be arranged with belly down in a slanting
position inside the container.
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8. โข 2. Chilled by Ice Slurry
- This is also termed as โSlush iceโ which is a mixture
of seawater and crushed ice used for the chilling of
fish catch.
Advantages of CSW(Chilled Sea Water) over icing:
โข CSW chills fish much faster than wet ice.
โข Fish in CSW do not suffer from physical damage due
to crushing or pressure from other fish.
โข Fish in CSW are washed in the slurry.
โข CSW chilled fish do not necessarily keep longer than
wet iced fish.
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10. Other Methods
3.Refrigerated Air
โข 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.
โข 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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13. 4. Dry Ice
โข Dry ice is solid carbon dioxide. Cooling is effected by the
evaporation of the dry ice.
โข 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. โข This method of chilling is preferred for air shipment of
fish, as this does not caused leakage.
โข 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
โข 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
โข Chilling equipment is classified by the method
used to remove heat, into:
โ mechanical refrigerators
โ cryogenic systems.
โข Batch or continuous operation is possible with
both types of equipment.
1. Mechanical refrigerators
โข Mechanical refrigerators have four basic
elements:
โ evaporator, compressor, condenser and expansion
valve.
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18. โข The refrigerator material (Copper) should have:
โ low thermal conductivity
โ high rates of heat transfer
โ high thermal efficiencies
โข 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. โ low boiling point and high latent heat of vaporization
โ dense vapour to reduce the size of the compressor
โ low toxicity and non-flammable
โ low miscibility with oil in the compressor
โ low cost
โข Ammonia has excellent heat transfer properties and is
not miscible with oil,
โ but it is toxic and flammable, and causes corrosion
of copper pipes.
โข Carbon dioxide is nonflammable and non-toxic,
making it safer,
โ but it requires considerably higher operating
pressures compared to ammonia.
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โขThe important properties of refrigerants are as follows:
20. โข CFCs are all non-toxic and non-flammable and have
good heat transfer properties and lower costs than other
refrigerants.
โ but, their interaction with ozone in the earthโs atmosphere.
โข Now, ozone-friendly HCFCs(Partially halogenated CFC)
are being developed and are likely to become important
refrigerants.
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21. Cryogenic chilling
โข A cryogen is a refrigerant that changes phase by
absorbing latent heat to cool the food.
โข Cryogenic chillers use solid carbon dioxide, liquid
carbon dioxide or liquid nitrogen.
โข Solid carbon dioxide removes latent heat of
sublimation.
โข The advantages of carbon dioxide include:
โ higher boiling and sublimation point than nitrogen,
and therefore a less severe effect on the food
โ most heat capacity arises from the conversion of
solid or liquid to gas.
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22. โข Solid carbon dioxide can be used in the form of โdry-
iceโ pellets, or
โ liquid carbon dioxide can be injected into air to
produce fine particles of solid carbon dioxide -
โsnowโ.
โ which rapidly sublime to gas.
โข Older meat processing, dry-ice pellets layered with
minced meat and filled into containers.
โ However, lack of uniformity distribution of pellets.
โ Result, some meat becoming frozen and some
remaining above 5ยบC
โ Which permitted bacterial growth.
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23. โข More recently the use of snow horns (Dry Ice Snow),
โ To distribute a fine layer of snow over minced
meat.
โ It is eliminated above problems and resulted in
rapid uniform cooling to 3โ4 OC.
โข Applications of cryogenic cooling include sausage
manufacture,
โ where carbon dioxide snow removes the heat
generated during size reduction and mixing
โ And cryogenic grinding where the cryogen reduces
dust levels, prevents dust explosions.
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24. Types of Insulation
โข The primary aim of using insulation in containers is
to slow down the rate of heat exchange between two
bodies at different temperatures.
โข 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
โข 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
โข 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)
๏ง It is widely used as an insulating material because it
is easy to produce.
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28. 4. Polyurethane
โข Expanded polyurethane has almost similar
properties (except for its lower compressibility
strength) as that of expanded polystyrene.
โข Polyurethane material can be foamed in situ on to
the surface that needs to be insulated.
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29. Effect on foods
โข Chilling foods to correct storage temperature causes
little or no reduction of eating quality or nutritional
properties.
โข Most significant effect of chilling,
โ Foods is hardening due to solidification of fats and
oils.
โข Lipid oxidation is one of the main causes of quality loss
in cookโchilled products,
โ Cooked meats rapidly developed oxidised flavour
termed โwarmed-over flavourโ.
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30. โข Quality deterioration:
โ Evaporation of moisture from unpackaged chilled
meats and cheeses.
โ Rapid staling of sandwich bread at reduced
temperatures and moisture migration from sandwich
fillings.
โข In cookโchill systems, nutritional losses are,
โ insignificant for thiamine, riboflavin and retinol.
โ but vitamin C losses are 3.3โ16% day1 at 2ยบC.
โข Vitamin C losses in cookโpasteurizeโchill procedures are
lower than cookedโchilled foods.
โ Spinach lost 66% within 3 days at 2โ3ยบC after cookโ
chilling compared with 26% loss within 7 days at 24ยบC
after cookโpasteurizingโchilling.
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