Freezing

1. Chapter 4
Freezing
By. Arman Napila Adion Barawiz. Bermon, LPT
Instructor 1/SSG-FSSG Adviser/BAT Extension
Coordinator/ITSO Officer/FAAEP/MNAS-SNCAT-SSCT AA
President/Faculty V-President/SSF DTI Manager

2. • becomes essential
when other means of
preserving fish, such
as icing, are unsuitable
or impractical.
Freezing

3. Freezing
• Chilling may keep fish between one to two weeks, while freezing
will keep fish, under proper conditions, for several months without
considerable changes in quality.
Freezing
• The freezing process usually does not affect the nutritional value or
flavor of the product, and ideally there should be no discernible
difference between the fresh and the frozen food
Freezing
• This could be attained when proper conditions (e.g., appropriate
freezing facilities, fresh raw material, adequate storage
temperature, and proper packaging) are strictly observed.

4. • is a way of stopping, either partly or
entirely, the deteriorative activities of
microorganisms and enzymes
Freezing
• The water in the flesh begins to
freeze at temperatures between -
1 and -3°C and, during freezing,
most of the water is converted
into ice
Fish contain
between 60-80%
water depending
upon the species

5. At -5°C, about 75% of the water in fish
muscle is frozen. Even at -65°C,
however, approximately 12% of the
water remains unfrozen.

6. There are three stages in the freezing
process:
Stage 1-Removal of heat.
This is the stage where the temperature
falls fairly rapidly to just below 0°C (the
freezing point of fresh water).

7. Stage
2
Conversion
of water to
ice
(crystallizati
on of
water).
Stage
3
Further
cooling
of
frozen
fish

8. The temperature of
fish flesh drops
rapidly again as
further cooling
occurs and most of
the remaining
water becomes
frozen.
The frozen fish
attains the
desired
temperature for
storage at
around -30°C.
.

9. Freezing time is the
time taken to reduce
the temperature from
its initial temperature
to a given temperature
(around -20 oC) at its
warmest (thickest)
part.
The final
temperature at the
thickest portion of
the fish must be
close to the
required
storage temperature
of -30°C.

10. 1. Slow
Freezin
g
Types of
Freezing
2. Quick
Freezing ("Snap
Freezing")

11. Slow Freezing
general, inferior quality products are
produced during slow freezing because of
protein denaturation.

12. denaturation
.
is a process in
which proteins or nucleic acids lose
the quaternary structure, tertiary
structure, and secondary
structure which is present in their native
state, by application of some external
stress or compound such as a
strong acid or base, a
concentrated inorganic salt,
an organic solvent
(e.g., alcohol or chloroform), radiation
or heat.

13. If proteins in a living cell
are denatured, this results
in disruption of cell
activity and possibly cell
death. Protein
denaturation is also a
consequence of cell death
The longer the fish is
allowed to be at -1 ° to -
5°C, the greater the extent
of denaturation due to
maximum enzyme activity
as well as maximum ice
crystal formation..

14. The zone of maximum
crystal formation is
between
-1 ° and -5°C. When
freezing takes longer
than 24 hours, the
resulting products wilJ
be of inferior quality
Very long
freezing times
can result in
bacterial
spoilage.

15. Quick Freezing
("SnapQuick
Freezing
("Snap
Freezing")
Quick freezing is a
general term
applied to most
freezing processes
and gives rise to
the term IQF or
individual quick
frozen

16. Quick freezing usually takes two hours or less to go through the zone
of maximum ice crystal formation (between -1 ° to - 5°C). The warmest
portion of the fish should be at -20°C at the completion of freezing.
Freezing
Systems
In the fishing industry, there
are three basic methods
available for freezing fish.
The choice of a freezing
system will depend upon
the cost, function, and
feasibility (location of plant
and type of product).

17. The methods of freezing are
Air Blast
Freezing
Air blast freezers
can be
continuous
(where the
product moves
through a freezer)
or batch type
(where the
product is
stationary).
A continuous flow of
cold air is passed
over the product.
Uniform freezing is
attained only if the
temperature and
speed of the air over
the product are
constant. Fairly high
air speed is
necessary to avoid
too long freezing
times.
Air blast freezers are very versatile;
therefore, they are useful in producing
individual quick frozen (IQF) products
of different crustaceans, fish fillet and
yalue added products such as breaded
portions or fish sticks

18. The main
disadvantages of
blast freezers are
that they occupy
a lot of space and
consume more
power than
equivalent plate
freezers.
Contact or Plate
Freezing
The product is
placed in direct
contact with
hollow, metal,
freezer plates,
through which a
cold fluid is
passed.
Contact or plate freezers are not as
versaWe as air blast freezers. Plate
freezers are used for freezing
products such as whole fish,
fillets, shrimps and other products
into blocks.

19. Spray or
Immersion
Freezing In this method, the
product comes into
direct contact with the
fluid refrigerant.
Spray or immersion
freezers are mainly
used for producing
very high value and
specialized
IQF products.
Spray or
immersion freezers
include liquid
nitrogen and
carbon dioxide
freezers.

20. Freezing Procedure
Raw Material
The freezing
process at below
-10°C will stop
bacterial action.
Chemical,
biochemical and
physical
processes leading
to irreversible
changes will occur
at a very slow rate
the state of the
raw material
before freezing
will determine
the quality of the
final product.
Freezing cannot
reverse
deterioration
that has already
occurred
Fish with a
certain degree
of pre-freezing
spoilage will
maintain it
through• out
freezing, frozen
storage and
thawing.
It is therefore
very important
to control the
quality of the
raw material,
and the
preparation of
fish for the
freezing
process.

21. Treatment
Before Freezing
Fish for freezing
must be kept well
iced or chilled
before freezing
iced water or
chilled seawater
(2 parts ice to 1
part water) can
be used to lower
the temperature
of the fish to or
close to 0°C.

22. Freezin
g
The freezing methods
employed will depend on the
type of product to be frozen.
Overloading of the freezer
must be avoided
The freezing time must be as
short as possible to prevent
quality loss. Freeze fish for
the correct length of time
(particularly important if the
fish or fillets are wrapped
before freezing; the thicker
the wrapping, the longer the
freezing time).

23. • If the fish had not been
packaged or wrapped (as
in the case of very large
fish) before freezing,
glazing (dipping or
immersion in iced water,
0°C) of the frozen fish
must be done
immediately after freezing
Treatment
After
Freezing
Glazing will prevent
dehydration (drying up) and
oxidation of the fish during
storage of the frozen fish.
Glazing must be renewed
when the ice coating or film
dissipates.

24. Packaging
The frozen fish must be handled
carefully during packaging. A proper
packaging material has the following
attributes: it should "fit" the product; it
should be airtight and should have
some degree of impermeability to air
and water vapor.

25. StorageFrozen products
must be kept frozen
in a cold store at the
recommended
storage temperature
(-30°C).
Delays during transfer of the
product from the freezer to the cold
store must be avoided. Frozen fish
must be handled with care since
they are brittle and easily
damaged.

26. Quality Assessment of Frozen Fish.
Frozen fish undergo some
changes during storage such as
the gradual development of off-
flavors and off-odors and other
physical deterioration.
The defects may pass
unnoticed, but after a
sufficiently long period of
storage these might intensify
and the fish become
unpleasant to eat.
The rate of quality loss will
depend on the storage
temperature and the extent
of temperature fluctuation.
Lipid
Changes
Rusting and rancidity are
brought about by the
changes occurring in lipids
during frozen storage of
fatty fish.
Rusting refers to the
movement of oil to the surface
of fish during cold storage,
resulting to a yellow or light
brown discoloration
The rust discoloration has been
ascribed to Maillard-type
reactions of amino acids or free
amino group of proteins with
reducing sugars or with some
lipid oxidation products.
Rancidity is the
unpleasant odor and
color that develop when
fats have undergone
oxidation during
storage.
It is characterized in its early
stage by a distinguished fishy
odor and flavor followed by an
unpleasant taint, described
as linseed oil or paint.

27. Freezer
Burn
This damage is due to excessive drying
resulting to matt (white patches on the
surface of frozen fish) and subsequent
change in the appearance of the thawed
product.
Dehydration and
Weight Loss.
During cold storage, dehydration of
frozen fish tends to occur naturally.
The surface flesh and
thin parts of the fish
become very dry and
porous.
This condition renders the
products totally unacceptable.
Loss in weight is due to
physical damage from
dehydration.
The loss is almost
insignificant (usually not
exceeding I%) provided
correct freezer and freezing
process are employed.

28. Development of Cold-Store Flavor and Odor
Frozen fish acquire
characteristic cold-store odor
and flavor due to improper and
extended cold storage.
Thawing of Frozen
Products
Quick thawing is as
important as quick
freezing in maintaining
the quality of frozen
fishery products.
The process of
thawing should have
no noticeable effects
on the quality of the
fish.
Alsot he condition of thawing should not allow
the growth of bacteria on the fish and the
surroundings. Thawing methods can be
divided into
two groups: those in which the
heat is directed into the flesh from
the surface and those inwhich
heat is generated more or less
uniformly throughout the flesh
the first group, beat is applied to
the surface of the fish by exposing
the fish to still or moving moist air,
by immersing them in or spraying
them with water or by allowing
water vapor to condense on them.
In the second group, the methods
depend
upon the absorption of electrical
power at mains, radio or microwave
frequencies.
Some methods are described below:

29. Thawing in Air
Still
Air
Frozen fish can be left
overnight at room
temperature (air
temperature should not be
higher than 20°C).
Provided the surface of
the fish does not become
too dry, the thawed product
is acceptable.
Thawing in air is in general
feasible only on a small scale
because substantial space is
required.
The amount of handling can be
extreme and the time taken is often
very long, even though it has the
advantage that limited or no
equipment is necessary.

30. Moving Air (Air
Blast Thawing)
Frozen fish can be thawed
much more quickly in moving
air. This can be done efficiently
by putting the fish on open mesh
trays stacked on frames or
trolleys in a tunnel not more
than 2 m high
The distance between
the trays should be
around twice the
thickness of the blocks
being thawed.
Air should be blown over the fish
at a temperature of 20°C and a
velocity of about 8 mis to attain
the shortest thawing time. The
flow should be uniform over the
whole cross section.

31. Thawing in
Water
Thawing in water can be a
cheap and easy way of
thawing whole fish provided
an ample supply of clean water
is available.
Thawing can be by immersion, by
spraying or by a combination of the
two. Thawing of fillets using this
method is not recommended because
they might become waterlogged and
may Jose much of their flavor.
Water for thawing should not be
warmer than 18°C and the
thawing rate should be at least 5
mm/s. Blocks of whole fish 10 cm
thick thaw almost totally in 4 1/2
hours under these conditions.