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Chapter 3CHILLING

Lecture by: Doname A. Reyes, RFT

PIF, Instructor

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INTRODUCTION• Since fish is highly perishable, proper handling

must start from the moment it is harvested until it reaches the consumer’s table. The fisher, the middleman (wholesaler and retailer) and the consumer all have important roles in keeping fish as fresh as possible. 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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• 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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METHODS OF CHILLING • 1. WET ICE (ICING) - Icing is by far the 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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WET ICE (ICING)

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• The following considerations must be taken when icing fish:

1. Sufficient ice must be used to maintain fish temperature at 00C. For longer trips more ice than fish is needed, more than the 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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• 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 and must be arranged with belly down in a slanting position inside the container.

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• 2. Chilled Seawater (CSW) or 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 over icing:- 1. CSW chills fish much faster than wet ice.- 2. Fish in CSW do not suffer from physical

damage due to crushing or pressure from other fish.

- 3. Fish in CSW are washed in the slurry.

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• In spite of the advantages mentioned, CSW chilled fish do not necessarily keep longer than wet iced fish.

ICE SLURRY

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3. Other Methods

• 1. Refrigerated Air • Air chilling is commonly employed in big

commercial boats. 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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Outdoor Air Cooled Process Chilling Refrigeration Models ( APS )

The APS chiller modules are used to conserve plant floor space by enabling the cooling system to be placed outside, either beside the building or on the roof.

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Refrigerated Air 2008 Refrigerator box

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• 2. 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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•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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• 3. 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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TYPES OF ICE • The most common types of ice used in fisheries are

the following:1. Block Ice• Block Ice made by freezing water in forms (cans or

moulds) of the desired size. • Ice blocks are rarely used directly for cooling fish

because of their size and weight. They must be crushed into smaller pieces. Block ice melts slowly but it is easy to transport in insulated containers to the villages.

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Block Ice

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• 2. Crushed Ice• Crushed ice usually comes from blocks or

slabs broken down through mechanical crushers or manually.

• Crushed ice is irregular in size with sharp edges.

Prawns on crushed ice

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METHODS OF STORING ICED FISH

• 1. Bulking • In bulking, the ice and the fish are layered to

achieve intimate contact, which will insure the maximum storage life in ice.

• This method of storing fish is usually utilized in the hold of fishing boats to economize on space.

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• Bulking has disadvantages when a very large volume of fish needs to be stored:

• 1. Fish can be physically damaged through the pressure of fish above and the pressure of ice.

• 2. In general, bulked fish are of poorer quality than shelved or boxed fish after the same storage time.

• 3. The unloading of the catch is difficult, which could result to rough handling.

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• 2. SHELFING – shelfing is applicable to larger species which are gutted. In this method, the fish is stored in single layers, gut cavity down on a bed of ice; sometimes a little ice is spread on top.

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SHELFING

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• 3. BOXING

• Boxing is the preferred method of sorting fish in ice. • Fish and ice are layered in especially made boxes.

The boxes can be easily be moved for transport to market or permanently fixed on board the fishing vessel.

Example of Plastic tote boxes for iced fish

Fish packed in ice in boxes usually maintain quality for longer periods than if kept on shelving or in bulk.

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• Several advantages of boxing:• 1. The segregation of first from last caught

fish, small from large, one species from another can be easily achieved.

• 2. Handling is kept to a minimum and with a good boxing practice fish will not be damaged physically.

• Disadvantages:• - a disadvantages of boxing in some cases is

that the space occupied in storing fish is greater than that for bulking.

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TYPES OF CONTAINERS• 1. Plastic box• Plastic is the term used to describe a

wide range of materials such as polyethylene (PE) and polypropylene (PP).

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• Classification of PE according to density: • a. Low density (0.91 to 0.925 g/cm3) • B. medium density (0.926 to 0.940

g/cm3) • C. High density: 1. type III (0.941 to 0.959 g/cm3) 2. type IV (0.960 g/cm3 and above)

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• High density or rigid polyethylene (HDPE) containers have proven to be very useful in the chilling of fish.

• Disadvantages:- They are expensive but will last long

• Advantages: - These containers can withstand extreme heat

or cold and are easy to clean because of their smooth and non-absorbent surface.

- The container can very well retain coldness inside.

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Polypropylene (PP) - It has a low density (around 0.902 g/cm3) - It is one of the slightest plastics, has a good resistance to grease and most chemicals,provides a good barrier to water vapor and canwithstand high temperatures due to its high

softening point.

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Polystyrene (Styrophore)- Chemically, polystyrene are resistant to

weak acids and bases, vegetable oils and other.

- Polystyrene boxes are becoming popular locally for transporting fish from the landing place to the market of fish plant.

- Disadvantage: difficult to clean, do not last long and do not have drainage for melt -water

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2. Galvanized Iron (GI) Sheet tubs (Banera)- Tubs made from GI sheets (banera) are conical in

shape and so far the most commonly used container by fishers in the Philippines. These tubs are not provided with drains; they easily corrode (rust); they have poor insulating property and are quite difficult to handle due to their fill capacity, around 40-50 kg.

- Banera are becoming less popular locally and are slowly being replaced by polystyrene boxes.

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Example of Galvanized Iron (GI) Sheet tubs (Banera)

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• 3. Wooden boxes • Wooden boxes can withstand rough handling

and have relatively good insulating property. However, they are not easy to clean, and are slightly difficult to handle because of their weight. They become a hazard to handlers (splinters can cause injury) when they are not properly maintained.

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• 4. Coconut, Bamboo or Rattan Baskets• These baskets are cheap and easy to handle due

to light material but difficult to clean and do not last long. Ice will easily melt in these baskets since they are insulated with coconut fiber pillows, the fish can be kept cool for 24 hours

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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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• 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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• 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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Coconut FiberTagalog:

Sawdust o kusot

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• 3. Polystyrene (styrophore) It is widely used as an insulating material

because it is easy to produce.

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• 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.