Stored Product

Prepared By:

Ahmed al janahi
Department of Fisheries
Ministry of Environment and Water, UAE

Recommended storage temperature

The recommended storage temperature for all frozen fisher y products in UAE is below -18°C and for chill products is below 4°C. Some products can be kept safely even at higher temperatures provided storage is only for short periods, but since it is not always possible to ensure that a product stays in store no longer than originally intended, it is generally safer to use -18°C storage at all times. Some of the poor quality fish on sale to the public has all too often been stored at a high temperature for a long time.

Even though fish are properly frozen, within a few hours of catching and then freezing at -18°C, they can not be kept indefinitely. The product will deteriorate very slowly eventually it becomes unattractive to look at and unpleasant to eat, although it may take years rather than months for this to occur. Usually fatty fish do not keep so well as low fat fishes.

Initial freshness of the fish influences storage life, old fish spoils more rapidly during cold storage than fresh fish.

Factors limiting storage life

There are certain factors limiting the storage/shelf life of frozen fishes. This mainly depends on the biochemical changes in the macromolecules namely proteins, fats and the loss of water (dehydration).

Changes in Protein

As a rule protein denatures at a temperature lower than optimum limit, and so are the enzymes. Its property completely changes during freezing and storage thereafter. Rate at which denaturation occurs depend largely on the temperature at which it was freezed. Even at temperatures below freezing point serious changes occur rapidly and the changes are so rapid that an initially good quality product can be spoilt within a few weeks. Protein denaturation is more obvious in low fatty fish than in fatty fish.

Deterioration of fish quality due to protein denaturation can therefore be checked by ensuring that storage is at as low a temperature as possible, preferably -18°C.

Fat changes

Like protein fat also get altered during cold storage. Fish oils readily combine with oxygen and get unpleasantly altered in presence of some of the muscle enzymes. Affected fish have an unpleasant odour and flavour, the fat becomes gummy, and the flesh develops a yellow, rusty appearance.

These changes take place more rapidly at higher temperatures of storage, and are sometimes accelerated by the presence of small amounts of certain chemicals like salts that probably increases the enzymatic activity. Since drying and the addition of salt accelerate the development of rancidity, frozen smoked fatty fish have a much shorter storage life than the frozen raw fish.

Dehydration changes

Even though processed and packed in good operating conditions, frozen fish may dry slowly in cold store. This is undesirable as most obvious reason that the product will lose weight and also it makes its texture and appearance negatively altered. Most importantly, drying speed up alteration of the protein and oxidation of the fat, both effecting shelf life of frozen fish.

Frozen fish that have suffered severe drying in cold store have a dry, wrinkled, toughened and pale appearance on the surface that is characteristic of the condition known as freezer burn. The skin of the thawed fish may have a similarly dry, wrinkled look, and if drying has been exceptionally severe, the flesh beneath can become spongy.

Design of cold stores

It is to be noted that for any long term storage of frozen fish, cold store should be capable of maintaining the recommended temperature of -18°C at all times as any fluctuation can degrade or even damage the product and encourage dehydration. Here are some general guidelines which are important and must be followed in order to maintain good quality for longer duration:

• Use storing methods which minimize deterioration of quality and increases shelf life . Chill products shall be held below 4°C and frozen products below -l8°C with minimal temperature fluctuation of ±3°C. Any drastic fluctuation in this temperature can affect the quality of fish.
• Never attempt to freeze fish directly in a cold store andnever put frozen fish that are warmer than the store directly into the store. Usually cold stores rarely has sufficient reserve capacity to cope with the extra heat load, warm product brought into the store will not only take a very long time to cool, but can also warm other products already in store resulting in consequent loss of quality.
• Separate facilities for chilling or freezing fish or fish products must be designed and constructed, to enable products to be reduced to the temperature within a prescribed time, appropriate to the product and process.
• Quick freezing rates must be maintained to prevent protein denaturation and tissue damage.
• Operators should be aware of the factors which affect freezing times, which includes:
  • Freezer type
  • Operating temperatures
  • Product type
  • Product temperatures
  • Product thickness and
  • Contact between the product and the freezing surface.
• Never stack goods directly on the floor of cold store, or close to the walls . Leave an air space below and around the goods so that cold air can pass between the goods and the store structure. Pallets can be used on the floor, and vertical battens can be fixed to the walls. It is recommended that products should be at least 4 inches off the floor, 8 inches away from walls and 18 inches from roof cooling units.
• Never leave the door openfor longer than necessary. In case having two doors never have more than one door open at a time as this will allow cold air go out and will increase the internal temperature.

• Freezers and cold storage compartments used for storing or holding fish shall be ofadequate size and design to provide proper separation and inspection of the materials.
• Premises of cold store/chill room must be located away from:
  • Environmentally polluted areas which pose a serious threat of contamination/spoilage/deterioration of quality of fish or fish products
  • Areas subject to water holding during rains, unless sufficient safety measures are taken
  • Areas prone to invasion of pests/rodents
  • Areas where wastes cannot be effectively removed
• Cold Store/Chill Room/Seafood storage facilities should be designed and constructed to:
  • Permit adequate maintenance and cleaning.
  • Maximum utilization of space.
  • Easy access to material.
  • Avoid pest access & harbourage.
  • Enable seafood to be effectively protected from contamination during storage; and
  • Wherever necessary, provide an environment that minimises the deterioration of quality of seafood .
• The cold store or chill room either made separately or made along with processing plant as a common facility, must be located, designed, and constructed so as to maintain the quality of seafood at its best.
• The facilities and internal structures, that may affect the quality or the shelf life of fish or fish products, must be of sanitary design.
• Any material used in building cold store or exposed internal surface finish or maintenance of facilities/internal structures, that may affect the suitability for storage of fish or fish product must:
  • Be impervious and free from depressions, pits, cracks, and crevices
  • Be easily cleaned and sanitised
  • Be unaffected by any corrosive substance with which it is likely to come into contact, to the extent it must not become a cause of spoilage of stored material
  • Be resistant to fracture, durable and capable of withstanding low temperatures, high moisture and normal cleaning and sanitising
  • In the case of surfaces (other than those used for walking or moving forklift), be smooth and minimise the accumulation of condensation
  • In the case of materials lining the walls, floors, and ceilings, be of a colour that does not disguise contaminants having regard to the lighting arrangements
• A Cold Store/Chill room must be designed and constructed so that:
  • It can accommodate maximum amount of material, goods can be stacked up to 20 feet or higher using fork lifts.
  • All internal angles between walls or other vertical surfaces and floors are coved to a radius of at least 9.5 mm.
  • The surfaces of walls, partitions and floors that are subject to wet cleaning must be constructed of impervious material, be easily and effectively cleaned, and facilitate the drainage or removal of water.
  • The floor is properly insulated and ventilated underground as large low temperature stores built directly on the ground often need ventilation under the floor insulation, or under floor heating, in order to prevent gradual build up of ice which may distort the floor or eventually wreck the building (this phenomenon is known as frost heave).
  • Ceilings and overhead fixtures must be constructed to minimise the build-up of dirt and condensation, and the shedding of particles.
  • All cooling pipes in the store should be defrosted at regular intervals; efficiency of the cooler will be considerably reduced if frost is allowed to accumulate.
  • Condensate from evaporative units in a cold store are collected and discharged to a drainage system located outside the store
  • Internal walls and partitions must be properly insulated. All the pillars and supports that pass through the insulation must themselves be well insulated as large amounts of heat can enter the store through un-insulated structures.
  • Windows must be easy to clean if any, constructed to minimise the build-up of dirt and, where necessary, fitted with removable and cleanable insect-proof screens. Where necessary, windows must be fixed.
  • Any racks, shelves, pellets or similar supports are constructed of corrosion resistant, smooth and easily cleanable non-absorbent materials. Pellets are properly painted with anti-corrosion paint, if made up of iron.
  • All doors should be :
    • Fitted with a rubber or similar seal which effectively prevents the escape of cold air or the entry of warm air when the door is closed, and the seal must be kept clean and disinfected.
    • Capable of being opened from the inside at all times.
    • Doors must have smooth, non-absorbent surfaces, and must be easy to clean and, wherever necessary, disinfect.
    • Filleted with air curtains or plastic curtain.
    • An unnecessary clutter of wiring, pipes, hangers, ducts, etc., shall be avoided.


• Adequate working space must be provided to allow for the hygienic performance of all operations, access of personnel, installation of equipment, effective cleaning, and effective monitoring and verification of activities.

• Product stacked close to the doorway should be screened to protect it from warm air coming in.
• The design and performance of the refrigeration system should be validated by an independent refrigeration consultant.
• Equipment for the control and accurate monitoring of temperatures and other refrigeration parameters (e.g. humidity, air-flow) must be provided and must operate at all times while refrigeration facilities are in use.
•  Every cool room must be equipped with a thermometer or thermograph indicating or recording temperature in the warmest part of the room accurate to ±1°C and located so that it is easily readable.
• Temperature equipments and the control room must be operated within their capacity and design capability and must consistently deliver required temperature.
• Temperature sensors must be maintained and placed in sufficient numbers to accurately monitor the temperature range in different parts of the room. If only one temperature sensor is used, it must be located in the return air flow to the evaporator unit as this usually has the highest temperature.
• The control devices may consist of an automatic system or manual system, either of which may use an indicating thermometer, a temperature measuring device or a temperature recording device if required depending upon the storage capacity of the cold store. If a manual system is used, the compartment should be fitted with an automatic alarm system to indicate a significant temperature change.

• For cold stores, room temperature should be recorded at interval no greater than 4 hours. For chillers, should be recorded at intervals of no greater than 1 hour.
• The temperature difference between the product and the cooling unit in the store must be kept as small as possible, since the bigger the temperature difference, the faster will water vapour leave the product to appear as frost on the cooler; thus freezer burn will be excessive when the temperature difference is large.
• Cold stores having common refrigerated air supply to freezers or chillers must comply with the following requirements:
  • Cold stores must be physically separated from the chiller/freezer by floor to ceiling walls
  • Insulation must be adequate to minimise heat transfer between the cold stores and chiller/freezer and the cold store
  • When a chiller/freezer is to be used to refrigerate unprotected fish or fish products, the inlet air from the cold store, if used to store packaged food, must be adequately filtered to remove any dust/contaminants prior to release into the chiller or freezer
  • Exhaust air from the chiller/freezer must not be released directly back into the cold store.
  • Exhaust air can be dealt by the following ways:
    • Discard directly to exterior environment.
    • Ducted directly to air inlet of the evaporator unit in the cold store
    • Reduced to the temperature of the cold store via a heat exchanger prior to return to the cold store.
• Lighting in the cold store must be of a sufficient intensity and quality to enable satisfactory performance of all operations.

• Packages of any one product should be removed from the store in the same order in which they were put in; all packages should be clearly date-stamped so that stock rotation, on the principle of first in, first out, can be strictly observed.
• Samples of products in store should be inspected at regular intervals and their temperature checked and recorded
• All products in store should be protected either by a wrapping that is impervious to water vapour, or by adequate glazing; glazing should be renewed at intervals when required.
• Any product that is expired and not fit for human consumption, but is suitable or fit for some other purpose, must be clearly identified and not be a source of contamination to any other product that is intended for human consumption.
• Loading facilities must be designed and constructed to protect seafood from environmental hazards and to ensure maintenance of the temperature of seafood during load in or load out.
• Loading facilities for protected food should be provided with a canopy.
• A maintenance programme must be documented and implemented to ensure that equipment and facilities are maintained in good working condition and do not cause any contamination of any product.
• All alterations, repairs and maintenance work on buildings, facilities and equipment should be done in a manner that minimises exposure of products to hazards introduced by this work.
•   The operator must keep the following records:
  • Temperature records
  • Repairs and maintenance records
  • Specifications and manufacturer’s instructions for all the equipments used in cold store/chill room
  • Any building reports
  • Refrigeration validation reports
  • Corrective action reports and
  • Internal audit reports.