Freezing fish and shrimp slows spoilage, increases shelf life, and prevents microbial growth and bacterial activity. There are two main freezing methods - slow freezing over 3-72 hours at -15°C to -29°C, and quick freezing within 30 minutes to 1 hour at -40°C. Freezing involves lowering the temperature through specific heat removal until most water in the fish tissue freezes into ice. Problems during freezing include desiccation, discoloration, toughness, and drip when thawed. Freezer types used include air blast, contact, immersion, and spray freezers.

1. FREEZING OF FISH AND SHRIMP
Fish freezing is a process of preservation in which the
temperature of fish and fishery products is lowered at –40°C or
below with most of the water inside of fish tissue turning into
ice.
 To slow down fish spoilage.
 To increase the shelf life of fish.
 To prevent the microbial growth.
 To prevent the bacterial activity.
Freezing
Slow freezing:
The temperature is usually –25°C or
lower, but may vary from –15°C to –29°C
and freezing may take 3 to 72 hours.
Quick freezing:
This is the process of sudden decrease in
the temperature of fish up to freezing.
The temperature is usually –40°C and
freezing time is 30 min to 1 hour.
I. The temperature falls fairly rapidly, at a more
or less constant rate, to just below 0°C while
the specific heat is being removed.
II. The temperature remains fairly constant at
about –1°C to –5°C while the latent heat is
being removed and the liquid water is
changing to ice; this is known as the Thermal
Arrest Period (TAP).
III. The temperature drops rapidly again while
the specific heat of ice is being removed and
most of the remaining water freezes
 Air blast freezers.
Cold air is circulated by fans over an evaporator.
Contact freezers.
Freezing by placing the products in
direct contact or plate freezers.
 Immersion and spray freezers.
Direct contact between a very cold liquid,
or gas from that liquid and the fish.
Bangabandhu Sheikh Mujibur Rahman Agricultural University
Gazipur-1706
• Desiccation starts from the surface of the body.
• Discolouration occurs due to break down of
haemoglobin.
• Toughness of muscle increases.
• Freeze-burn occurs.
• Thaw-drip or water drip occurs when frozen fish
are thawed slowly.
• Proteins irreversibly dehydrated.
Solutions
o Freezing and storing at an ambient temperature of -
4°F (-20°C) or below for 7 days.
o Brining and pickling may reduce the parasite
hazard in a fish.
o Should maintain hygienic condition during
freezing for avoiding contamination.
Freezer Types
Course Title: Fish Processing-I Course Code: FIT 302
Figure: Effect of Freezing
 Quality of frozen shrimp
depends on the freshness of raw
materials.
 For block freezing, the graded
shrimps are weighed and
packed in wax laminated
cartons with a lining of water-
proof material.
 For individual quick freezing
(IQF), the blanched or graded
shrimps are individually loaded
into the conveyer of the IQF
machine and frozen rapidly in
the freezing chamber.
Freezing Method of Shrimp
Principles of freezing
Purpose of Freezing
Problems during Freezing
Submitted To:
Md. Golam Rasul
Lecturer
Dept. of Fisheries Technology
Faculty of Fisheries
Submitted By:
Subrina Nasrin (14-05-3288)
Shamima Yeasmin Dipu(14-05-3289)
Deepto kundu (14-05-3290)
Bony Amin Piash (14-05-3291)
Md. Shathil Talukder (14-05-3293)