freezing method of fish and shrimp

FREEZING OF FISH AND SHRIMP

Fish freezing is a process of preservation in which thetemperature of fish and fishery products is lowered at –40°C orbelow with most of the water inside of fish tissue turning intoice.

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 orlower, but may vary from –15°C to –29°Cand freezing may take 3 to 72 hours.

Quick freezing:This is the process of sudden decrease inthe temperature of fish up to freezing.The temperature is usually –40°C andfreezing time is 30 min to 1 hour.

I. The temperature falls fairly rapidly, at a moreor less constant rate, to just below 0°C whilethe specific heat is being removed.

II. The temperature remains fairly constant atabout –1°C to –5°C while the latent heat isbeing removed and the liquid water ischanging to ice; this is known as the ThermalArrest Period (TAP).

III. The temperature drops rapidly again whilethe specific heat of ice is being removed andmost of the remaining water freezes

Air blast freezers.Cold air is circulated by fans over an evaporator.

Contact freezers.Freezing by placing the products indirect 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 UniversityGazipur-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.

Solutionso 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 shrimpdepends on the freshness of rawmaterials.

For block freezing, the gradedshrimps are weighed andpacked in wax laminatedcartons with a lining of water-proof material.

For individual quick freezing(IQF), the blanched or gradedshrimps are individually loadedinto the conveyer of the IQFmachine and frozen rapidly inthe freezing chamber.

Freezing Method of Shrimp

Principles of freezing

Purpose of Freezing

Problems during Freezing

Submitted To:Md. Golam RasulLecturerDept. of Fisheries TechnologyFaculty 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)