FISH HANDLING AND PROCESSING

By

Dr. Geeta ChauhanSenior Scientist

Division Of Livestock Products Technology

Indian Veterinary Research InstituteIzatnagar, Bareilly (U.P)

INTRODUCTION

After independence, India has made glorious achievements in food production and have witnessed multicolor revolutions in terms of green, yellow, white and blue.

As compared to food grains, milk eggs and other foods, country’s fish production has increased at a higher rate.

This sector is contributing 1.2% to the national GDP and 5.3% to the agricultural GDP.

Fish is a highly perishable commodity requiring a cautious handling and careful processing.

To ensure best quality, appropriate technologies and processes must be followed with clean and hygienic conditions.

KEEPING QUALITY OF FISH

The physical, chemical and bacteriological characteristics of fish are influenced by the species, seasons, catching methods and fishing grounds etc.

The characteristics of fresh fish are- Shining, iridescent surface covered with a nearly transparent, uniformly and thinly spread slime. protruding eyes with a jet black pupil and transparent cornea gills that are bright and free from visible slime flesh is soft and flabby, tending to retain finger indentations the flesh odor is ‘marine’, ‘fresh sea weedy’ or laky in addition pleasant, margarine like odor in case of fatty fish.

As the spoilage is developed in fish- its structure loses bright sheen and color and slime becomes thicker, turbid and lumpy lately, Slime becomes yellow or browneyes sink and shrink with cloudy and milky pupil and opaque cornea gills become bleached, light pink in color, finally turning to grayish brown covered with a thick slime. flesh becomes soft and inelastic and may be easily stripped from backbone and extrudes juice under light pressure. odor changes from ‘sweetish’ then ‘ammoniacal’ or ‘fishy’ and finally putrefaction odor.

CAUSES OF SPOILAGE

The fish spoilage may be caused by 3 causes-a)Bacteriab)Digestive enzymesc)Others such as oxidation, etc.The flesh of freshly caught fish is sterile while the spoiling microflora is present in external slime and digestive tracts.Fatty fishes may develop spoilage due to all 3 above mentioned causes.If not gutted soon after catch, strong digestive enzymes affect the viscera and belly walls and cause discoloration- ‘ belly bum’ or disruption- ‘ torn bellies’.

HANDLING OF FISH

Handling of market fish

Fish should be purchased as fresh or frozen as possible Exposure to unsafe temperature should be avoided Exposure to contaminants should be avoided by keeping fishes in plastic bag It should be kept in refrigerators at home Raw fish purchased should not come in contact with cooked fish, other cooked food stuffs and raw fruits and vegetables as raw fish contains bacterial loadIt should be stored at proper temperature- if hot, temperature should be 140ºF and if to be kept cold, temperature should be 40ºF or less.

Handling of fresh catch

Efforts should be done to keep the fish alive as long as possible- by keeping in metal link basket or live box. The fish should be checked for signs of disease or parasites or for any abnormal growth in the flesh. It should be made certain that the fish is being taken from safe water without any contaminants. If it is difficult to keep fish alive, it should be stored at temperature below 40ºF.

GUTTING, CLEANING AND COOLING

The harvested fish should be cleaned and cooled as soon possible due to their strong digestive juices, fish spoil very soon and if not gutted and cleaned promptly may develop off flavour and color.A sharp knife, clean cloth, plastic bags and crushed ice must be kept ready for gutting and cleaning of fish.With the help of knife, fish should be cleaned and bled.Throat should be cut and gills and entrails are removed.Cleaned fish first be put in plastic bags and then in ice. To prevent contamination, hands, working area, cutting boards, knives and other utensils should be properly cleaned with water and soap.

PREPARATION OF FILLETS

Wash the fish in clean cold water to remove blood, microbes and enzymes.

Filleting is done with a sharp knife with flexible blades.

The fillets collected should be stored properly at low temperature.

PROCESS OF FILLETING

Fish is cut behind the pectoral fin straight down to the backbone and cut is angled towards the

top of the head↓

Knife is run along one side of the backbone, scrapping the rib bones without cutting them

↓The knife is pushed through the flesh near the vent just behind the rib bones and fillet is cut

free at the tail↓

Flesh is cut carefully away from the ribcage.↓

The first boneless fillet is removed by cutting through the stomach skin.

STORAGEAfter cleaning and packaging the fish should be stored either by refrigerating or freezing.

Refrigerating-Raw fish can be kept in refrigerator at the temperature of 40ºF or lower.Should be stored in covered containers.While keeping in refrigerator, fish should be moist but not wet.For refrigerating fish at home, the fish should be removed from wrapper, rinsed properly in clean cold water, pat dried with paper towel and kept in a plate or pan lined with double layer of paper towels.The pan should be covered tightly with aluminium foil or plastic wrap to avoid leakage.This covered fish may be kept in the coldest part of the refrigerator.

Freezing-It is done if the fish is not to be used within 2 days of the catch or to be transported.It must be properly cleaned and handled before freezing.The temperature of freezing fish should be 0ºF or less.Following methods can be used for freezing the fish-

A.Double wrapping-Suitable for small whole fish, steaks or fillets.In this, fish is tightly wrapped individually in plastic wrap and again wrapped tightly with another layer of wrap.These wrapped pieces are kept in a sealable freezer bag or may be wrapped tightly in aluminium foil.The sealed bags are placed scattered in freezer and when they are frozen, they can be stocked on top of each other.

B. Freezing in ice block- This method is suitable for steaks and

fillets. It protects the fish from freezer burn and

avoids the exposure from air. For freezing fish in ice box, it is cut into

small pieces and placed in containers. Head space of one inch should be left for expansion.

Fish is then covered with cold water and kept in freezer to freeze.

Check whether fish is completely covered with ice or not.

When freezing is done in a pan, the ice block is taken out by running little cold water at its bottom and ice block is double wrapped and kept in freezer.

C. Glazing-

This method is suitable for whole fish or large cuts.

In this method, fish is first frozen by placing them on a baking sheet in a single layer and the frozen fish is then dipped into a container having ice water and allowed to freeze again.

This process is repeated until an ice coating of at least 1/8” thickness is made on the fish.

It is then put in an airtight freezer bag or container and kept in freezer.

At interval, glazing should be checked.

CARE DURING FREEZING

The package should be marked with content and date.

Wrapped package should be sealed tightly.

When fish is frozen, make sure its fully covered with ice.

Frozen fish brought from market should be put in the freezer at the earliest and in the original package only.

Putting the fish package in freezer bag before keeping in freezer to provide an extra protection.

SUPER CHILLINGThis method is appropriate when freezing facilities are not available and fish have to be transported.If followed properly, freshness can be maintained for six to seven days.For super chilling, fish are cleaned and wrapped tightly as whole with two layers of plastic wrap or aluminium foil.A mix of rock salt and crushed ice in 1/20 is prepared.For placing a fish for chilling, a four inch layer of plain crushed ice is put at the cooler bottom and wrapped fish are placed on it in a single layer. On this, ice mix layer is put. The process is repeated till fish are covered.Finally, the cooler is tightly covered.During transportation, water drain may be left open or cooler should be removed in between and water should be drained off. Accordingly, the ice mix should be put again.

POINTS TO REMEMBER DURING STORAGE OF FISH

Fish must be cleaned thoroughly. Refrigerator temperature should be 40ºF or low. Thawed fish should not be refrozen again. Thawing should be done in refrigerator or cold water that must be changed at every half an hour. Fish should be frozen as soon as possible after the catch. The package should be mentioned with content and date.

PROCESSING OF FISHRaw and fresh fish are given different treatments through different processing methods for the purpose of-Long storageEnhancing sensory characteristicsThe common techniques of fish processing include scanning, smoking, salting, drying and fermentation.

1.Canning-In canning fish, high heat treatment is given to destroy the present bacteria and the product is packaged in hermetically sealed containers to protect against recontamination.Canning provides shelf stable fish and so freezing space is not required. Canning may keep the fish fresh for even years.For canning fish, only half-pint or pint-jars must be used, quart jars not to be used. These jars should be thoroughly cleaned with hot soapy water.

Glass jars with glass threads are best for fish or meat canning.Any one of the 2 lids types may be used for the jars-Glass lids used with separable rubber sealer ringMetal lid to which a sealing compound is already applied and over which the metal band is screwed.The process of canning involves following steps-

1.Preparation of fish-Fish are gutted, gilled and iced down as soon as possible.Fillets can be prepared.Large fish may be cut into smaller pieces.Washing is done in clean and cold water and proper draining is done to make them quite dry.

2.Cleaning of jars-Jars are cleaned and sterilized.

3. Filling of jars- Sterilized, clean jars are packed with cleaned

fish During filling, head space of an inch must be

left, so that the seal is not disturbed. There should not be any air pockets left.

4. Closing of jars- Warm, dried lids are put on jars and rims are

tightened. Lids with sealing compound, requiring boiling or

holding in warm water before use may handled so as per the directions of the manufacturers.

5. Heating of jars- Sealed jars are placed in pressure canner and

heating is done. The pressure canner should be in perfect order

and directions given to work with it to avoid the risk of botulism food poisoning.

2. Smoking- It is done for 2 purposes- For preservation For texture and flavor. Smoking is much common in less developed

countries where refrigeration and transportation facilities are not very good.

Smoking is very popular in developed countries for taste.

Steps in smoking includes-

1. Preparation/cleaning of fish-Scales, head, fins, tail, viscera are removed and fish are washed with clean cold water.

2. Curing of fish-It can be done in two ways-

a. Wet/brine curing- Ingredients used for brine curing are 3 cups

table salt, 1½ cups brown sugar and 1 gallon of cold water. Other spices may also be added as per the choice.All these are mixed properly in a non-metallic container.

Fish is completely immersed in brine. One gallon of brine is sufficient for curing four pounds of fish.

It is then refrigerated or kept in ice bags to keep the fish cool.

Brining is done for 2 to 6 hours.

b. Dry curing- In this salt is rubbed directly on the fish. For this, three parts of brown sugar is mixed

with one part of non-iodized salt and fish fillets are placed in a deep non-metallic pan.

The piece is covered with dry cure mix and kept in refrigerator for 18-24 hours.

During dry curing, moisture will come out of the fish, making liquid brine.

After curing, fish are taken out, rinsed lightly, pat dried and placed on paper towel and air dried for one hour.

3.Drying of fish-Cured fish are dried before smoking.Drying forms a pellicle or glaze on the skin, which keeps moisture in and contamination out and allows the smoke to adhere properly to get smoky flavor and uniform color.Drying can be done in cool shady place or in smoker racks.

4.Smoking-The fish may be cold or hot smoked.Smoked fish may be kept for many months in freezer but in refrigerator, cold smoked fish may be preserved for several months but hot smoked may be kept only for a week.Smoking requires- a smoke source, a smoking chamber and an air ventilation system.

a. Cold smoking- The fish is smoked at low temperature for long

time. For this, fish is placed in smoker having

temperature maintained at about 80ºF. It should not exceed 90ºF else it will become cured and cooked and unsafe for consumption.

The smoking time for small fish may be 24 hours and for large fish it may be 3-4 days of continuous smoking.

b. Hot smoking- In this, fish is placed in smoker having

temperature of not more than 90ºF for the first two hours. During this period, fish will get a brown color.

The temperature is then raised gradually to about 175ºF and smoking is done for 4-8 hours.

5. Cooling and Packaging-After smoking is completed, the fish are cooled and then packaged in suitable packaging material and stored.

3. Salting of fish- Salting of fish is an art as well as a science. This process is affected by weather, size and

species of fish. For salting, good quality fish should be chosen

and proper cleaning should be maintained. Following operations are followed for salting

fish-

1. Preparing the fish- Beheading, gutting, bleeding and cleaning of

fish should be done as soon as possible. Larger fish can be cut into suitable pieces.

2. Salting- The bottom of water proof vat is covered with a

thin layer of salt and fish are layered on it with flesh side up.

Fish layer is covered with thin layer of salt leaving no space. In the same manner two or three layers of fishes are placed.

Then fish is reversed with skin side up covering them with salt layer. The top layer is always a salt layer.As due to salt, moisture comes out and brine is formed. The brine is kept saturated by adding more salt.Because of moisture loss, fish level is fallen and accordingly more fish may be placed along with the salt layer.The fish may be cured for 12-15 days in warm weather and 21 days or more in cold weather.Properly salted fish flesh is translucent, firm but yields to light pressure.3.Washing and drying to remove extra salt-After salting, fish are washed in unpolluted sea water or fresh brine and put on plain surface, applying pressure on them to remove moisture and make them thinner.4.Drying-

Salted fish may be dried in sun or by artificial heat and air generated by fans.

4. Drying and Dehydration- Oldest method of preserving perishable food

items like fish and is considered as least costly method.

Two common methods for drying fish are-

a. Sun drying-Advantages-

Due to high concentration and diminished water content, spoilage due to microbes and enzymes are avoided.

It is simple and inexpensive method. Further, dried fish may be stored at most

ambient temperatures.Demerits-

No control over drying conditions. Dependency on natural weather Greater chances of contamination with dirt and

dust and infestation with insects, their eggs and larvae.

b. Dehydration- The drying carried out in controlled conditions. Dehydrated fish have high quality and longer

shelf life than sun dried fish. Various driers like cabinet drier, kiln drier,

tunnel drier, etc are used.

5. Fermentation- Fermented fish have been considered as a

Southeast-Asian product for long. Fermented fish products are prepared by salting

and fermenting the fish to convert the flesh into simple components.

Fish fermentation lasts for 3-9 months and the flesh liquefy or becomes like a paste.

Fermented fish means any fishy product having degradative changes due to enzymatic or microbial activity.

Some common fermented fish products are- Nuoc-man of Vietnam, Nam-pla of Thailand, Sushi of Japan and Patis of Philippines.The main fermentation procedures are-i.Fermentation with salting and dryingii.Fermentation and drying without saltingiii.Fermented with salting but without drying.

CONCLUSION

Fish is a highly perishable product and can be handled safely to improve its shelf life. Different processing methods like canning, drying, smoking, etc if applied properly to the fish as soon as the fish is caught, can enhance the shelf life from months to years depending on the methods used. The processed fish can be transported to the distance places without the risk of spoilage and food poisoning.

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