Ice and cooling
Quality and safety issues in fish handling
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A course in quality and safety management in
fishery harbours in Sri Lanka
NARA, DFAR, ICEIDA and UNU-FTP
Department of Fisheries and
Aquatic Resources (DFAR)
National Aquatic Resources Research
and Development Agency (NARA)
United Nations University Fisheries
Training Programme (UNU-FTP)
Icelandic International
Development Agency (ICEIDA)
Sri Lanka
Sri Lanka
Iceland
Iceland
Content
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Properties of ice
Thermal properties of fish
Different types of ice
Use of ice
• for cooling of fish
• for keeping fish cold
Learning objectives
• After this lecture the participants will know:
• correct use of ice
• how to estimate the amount if ice needed in various
situations
Purpose of cooling
Temperature
Rate of activities
(Enzymatic, Microbiological and
Chemical reaction)
Rate of Spoilage
Shelf Life
Why use ice?
• Ice has a high cooling capacity and melts at a definite
temperature (0°C)
• Ice is used to cool the fish to preserve it’s quality
• Ice keeps the fish moist and will wash surface bacteria, blood
and slime from the fish as it melts
• Clean ice is harmless and relatively cheap
• Ice keeps fish cool during storage and transport
Availability of ice
• The availability of ice depends on:
• availability of clean water
• an ice plant at the harbour site
• The quantity of ice needed in a harbour depends on
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the quantity of fish passing through the harbour
the number of one day vs. multi day boats
the surrounding temperature and sea temperature
the transport distance from harbour to the next link
Properties of ice and water
• Ice melts at 0°C
• 80 kcal are needed to melt 1 kg. of ice
• 1 kcal needs to be removed from 1 kg water to
cool it by 1°C
Properties of ice, cont.
1 kg of ice can cool roughly 3 kg of water from 25°C to 0°C
=
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1 kg ice
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3 kg 25°C water
=
4 kg 0°C water
Thermal properties of fish
• Depend on fish composition
• mainly water and fat content
Lean
Semi fat
Fatty
% fat
<1
< 10
< 20
Kcal/kg °C
0,88
0,83
0,78
Kg fish cooled
from 30->0°C by 1
kg ice
3,0
3,2
3,4
Thermal properties of fish, cont.
• In reality more ice is needed due mainly to
heat loss to the surroundings during cooling
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surrounding air
fish hold / box
water that may be present
etc .....
• More ice is also needed to keep the fish cool
for any length of time
How does ice cool
• Ice cools by melting
• the ice takes up heat from the fish and melts
• The melted water (0°C) can further cool the
fish when it flows over it
Cooling rate
• Cooling rate depends on
• Type of ice (flake, crushed block, slurry ...)
• Adequate contact of ice with the fish
• Fish size (surface/volume)
• small fish cool faster than big fish
• Fish species
• fat and water content
• fish with thick skin cool slower than fish with thin skin
Types of ice and cooling media
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Flake ice
Block ice and crushed block ice
Ice slurry
Liquid ice
Chilled seawater
Refrigerated seawater
Dry or gel ice
Flake ice
• Larger heat-exchange surface
: faster and more efficient
• Slightly sub cooled easy to
store and handle
• Ready to use, less handling
than block ice
Flake ice
Block ice
• Produced in large
chunks
• Big ice chunks melt
slower than small
(surface/volume)
• Can be transported
before crushing
• Particle size depends on
crushing machine
Ice slurry
• Flake or block ice
crushed to small ice
particles and mixed with
seawater or water
• Good for cooling
• Not as good for keeping
cool unless drained
• Stagnant blood water
• salt uptake
Liquid ice
• Very small ice particles
form in salt water /
seawater
• Very good cooling
properties
• Not as good for keeping
cool unless drained
• stagnant blood water
• salt uptake
Chilled Sea Water (CSW)
• Seawater and ice mixed in a
container or hold
• agitated by blowing air
up through the mixture
• Good for quick cooling
• Salt uptake can be a
problem if fish is in CSW
for a long time
Refrigerated Sea Water (RSW)
• Seawater cooled by mechanical means
• seawater is circulated from fish container/hold,
through a refrigirating unit and back to the
container/hold
• Good for quick cooling
• Salt uptake can be a problem if fish is in RSW
for a long time
Properties of different types
• Ice liquid mixtures +RSW
• completely surround the fish
• have good heat transfer properties
• cool fast
• In case of seawater
• salt uptake can be a problem if fish is kept long in
the mixture
Properties of different types, cont.
• Ice particles (flake ice and crushed block ice)
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cool slower (do not completely surround fish)
have lower heat transfer
no problem with long time storage (no salt uptake)
cleans the fish as it melts
Bulk density of various types of ice
Flake ice
4-500 kg/m3
Tube ice
5-600 kg/m3
Block ice
6-700 kg/m3
Ice
920 kg/ m3
Ice slurry/liquid ice
850-900 kg/m3
Time of cooling
• Depends on:
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type of fish (thermal properties)
initial temperature of fish
type of ice
shape of fish (thickness)
size of fish
method of iceing
Temp. (°C)
Cooling rates in the center of cod - comparison of flake ice and liquid
ice
Flake ice
Liquid ice
Time (hours)
Amount of ice needed
• The amount of ice needed depends on:
• temperature of fish
• surrounding temperature and conditions
• is the fish kept in isolated boxes
• is the fish hold isolated
• etc...
• the length of time the fish is to be kept on ice
• storage on board
• transport
Transport with ice and cooling
Transport with ice
Amount of ice – cooling fish
100 kg of fatty fish at 25°C needs to be cooled to 0°C with ice
- 1 kg of ice can take up 80 kcal og heat when melting
- to cool 1 kg of fatty fish by 1°C 0,78kcal have to be removed
How much heat to remove?
100kg * 25 °C * 0,78 kcal/kg °C = 2610 kcal
How much ice will that melt?
2610 kcal / 80 [kcal/kg ice] = 32.6 kg of ice
OR ABOUT 1 KG ICE pr. 3 KG FISH
Amount of ice – keeping cool
• Very difficult to estimate
• Depends on the conditions
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duration
weather
degree of insulation
where in hold/vehicle the fish is kept
• Experiments have been made...
Results of ice meltage tests
importance of insulation
Results of ice meltage tests under field conditions.
(·) plastic box in the shade,
(x) plastic box in the sun. Plastic boxes, 40 kg capacity, red
colour, unstacked, flake ice, external average temperature (dry
bulb) 28°C. (Data obtained during the FAO/DANIDA National
Workshop on Fish Technology and Quality Control, Bissau,
Quality and quality changes in fresh fish
FAO FISHERIES TECHNICAL PAPER – 348
Guinea-Bissau, March 1986)
H. H. Huss
Results of ice meltage tests
importance of insulation
Results of ice meltage tests under field conditions. ( · ) standard plastic box (not insulated) 40 kg
total capacity, (x) insulated plastic fish container (Metabox 70, DK). Both kept in the shade, unstacked, flake ice, average external temperature (Te) 28°C. (Data obtained during the FAO/DANIDA
National Workshop on Fish Technology and Quality Control, Bissau, Guinea-Bissau, March 1986)
Quality and quality changes in fresh fish
FAO FISHERIES TECHNICAL PAPER – 348
H. H. Huss
Results of ice meltage tests
importance of placement
By insulating around the
storage area (transport
truck, ship hold...)
differance in ice melting
rates can be reduced
Results of ice meltage tests during storage in a stack of plastic
boxes. Plastic boxes 35 kg in a chill storage room at 5°C, flake ice
(from Boeri et al. (1985)
Quality and quality changes in fresh fish
FAO FISHERIES TECHNICAL PAPER – 348
H. H. Huss
Amount of ice - example
200 kg of tuna needs to be cooled from 28°C to 0°C and transported
for 4 hours at surrounding temperature 28°C
The tuna is packed in polystyrene boxes (70X50X50cm).
Approx. 65 kg of ice is needed to cool the tuna
If the tuna is transported in an uninsulated truck
22 kg of ice is needed during transportation
If the tuna is transported in an insulated, refrigerated truck at 3°C
2 kg of ice is needed during transportation
Methods of icing raw material
There are two main methods of icing raw material:
• Direct Contact Icing (DCI): suitable for icing of
fish and shrimp.
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Non-Contact Icing (NCI): suitable for icing of
squid, cuttlefish and octopus.
(Bao, Quang, Vn-pr., 2003)
Non-Contact Icing Method (NCI)
• Raw material is
individually packed
in polyethylene bag.
• Raw material is packed
in layer with plastic
sheet and ice.
(Bao, Quang, Vn-pr., 2003)
Handling ice
• Ice used for cooling fish needs to be handled
with the same care as the fish itself
• contaminated ice means contaminated fish
• Ice should be kept in insulated boxes/places
• will minimize melting prior to use
Quality and safety of ice
• Depends on:
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quality of water
conditions in production (hygiene etc..)
storage of ice
handling of ice
• The ice is part of the processing/product
References
• Shawyer, M.; Medina Pizzali, A.F. The use of ice on small fishing vessels.
FAO Fisheries Technical Paper. No. 436. Rome, FAO. 2003.
• Graham, J.; Johnston, W.A.; Nicholson, F.J. Ice in Fisheries FAO Fisheries
Technical Paper. No. 331. Rome, FAO. 1992.
• Training material from UNU-FTP/Icelandic Fisheries Laboratories