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Handling refrigerated cargoes- Fresh Produce (Fruit and Vegetables) & Frozen Cargo

Refrigerated cargoes include meat carcases, carton (packed) meat, fruit, cheese, butter, fish and offal. Ships are specifically designed for their carriage, with separate spaces in holds and ’tween decks, each fitted with suitable insulation and individual control of ventilation.

refrigerated-fruits
Refrigerated fruits

Fresh Produce (Fruit and Vegetables)

In general, fresh produce is carried under temperature control . It is customary for shippers to produce written carriage instructions, lays down general guidelines for background and emphasises some of the essential characteristics of fresh produce.

Fruit and vegetables are living and so respire, taking in oxygen from the air and producing carbon dioxide. As noted in the section on temperature control, this process involves the production of heat, hence the need for temperature control.

For short voyages of no more than three or four days, fruit picked at the right time, i.e. not already ripe, can be carried without refrigeration. In general, all fruit and vegetables must be properly ventilated even if carried at ambient temperatures. Fruit should not be stowed with any other cargo that might pick up taint, e.g. flour, tea, coffee, etc.

Carriage temperatures for fresh produce fall into two clearly defined categories. Produce that is tolerant of low temperatures is carried in the temperature range between ­5°C and +0.05°C. Most vegetables consist largely of water and thus have a freezing point closer to zero than most fruits. Consequently, the carriage temperature for vegetables must not fall below zero. Carriage is effected at temperatures near to the freezing point of the produce, taking into account the sensitivity of the temperature control equipment to avoid freezing part of the cargo. Typical examples are apples, pears, cherries and kiwifruit, and most vegetables.

However, some produce is more sensitive to low temperatures, so must be carried at higher temperatures which represent a compromise between the harmful effects of low temperature (chill damage), and the beneficial effect of low temperatures in retarding ripening and alleviating microbiological damage. Typical examples are bananas, avocado, pineapple, melons, aubergines, ginger, marrow and squashes. Produce that may be very sensitive to lower temperatures will always have written carriage instructions from the shipper and, indeed, such cargo should not be accepted without such instructions. Examples are bananas, plantains and pineapples.

Some vegetables can be carried without refrigeration, but with special ventilation requirements. Examples are onions and potatoes. The method adopted will depend on the length of the intended voyage, ambient conditions and the required shelf life.

frozen-fish
frozen-fish

Frozen Cargo

This is cargo that has been deep frozen prior to loading and should be at a temperature of ­18°C or lower with the task of the ship to maintain the deep frozen condition. In some instances there are legal requirements to carry particular commodities at a temperature below a certain value . Deep frozen cargoes are not living, and do not respire or produce heat, so the task of the refrigeration system is much simpler.

Most frozen cargo is shipped in cartons on pallets in reefer ships or refrigerated containers. However, on the rare occasion when a breakbulk cargo is loaded, extra checks may be necessary, particularly if the commodity is carcass meat.

Carcasses with soft flanks must be returned for re-freezing before stowage in the ship otherwise badly distorted carcasses will result on discharge with consequent claims against the ship. Particular care should be taken to see that soft carcasses represented for shipment have not just received a cold blast to freeze the outside flank which will now appear in a good hard condition whilst the inside is still warm. Thus it may be necessary to drill into the frozen meat and use a spear thermometer to ascertain the actual bone temperature. Blood-stained shirts will indicate that a carcass has at least partially thawed since initial freezing and should be considered with suspicion.

Again, if soft or wet carcasses are stowed in this condition they may well distort, nesting one into another and blocking the airflow. If wet from partial thawing (or rain) they may freeze together, resulting in considerable damage when prised apart on discharge. Similar problems can arise with cartons of frozen produce which must be clean, dry and free from frost at time of loading.

Insulation and refregerants

Ordinary general cargoes may be carried in the spaces at other times, the temperature being regulated accordingly for the type of cargo being carried.

Dedicated reefer ship
Dedicated reefer ship

Insulation around a compartment consists of either a fibreglass or polystyrene type of packing over the steelwork of the vessel, with an aluminium alloy facing. This insulation is comparatively fragile and requires regular inspection and maintenance.

Cooling a compartment on modern vessels is achieved by circulating pre-cooled air by means of fans.The air is cooled by an ordinary refrigeration plant employing a refrigerant with the most practical qualities, namely, a high thermaldynamic efficiency, low costs, low working pressure, low volume non-toxicity, non-inflammability, non-explosivity and ready availability from numerous sources.

Typical Refrigerants :
Carbon dioxide (CO2). Non-poisonous, odourless, with no corrosive action on metal. It has a low boiling point but a high saturated pressure. Ammonia (NH3). Poisonous vapour, and therefore requires a separate compartment of its own. It will corrode certain metals, e.g. copper. Has a lower saturated pressure than CO2.

Freon (CCl2F2). Non-poisonous, non-corrosive, and has a low saturated pressure. By far the most popular in modern tonnage.

Loading precautions

Absolute cleanliness is required during the loading of refrigerated cargo, and the following points should be observed:
  1. The compartment should be cleaned of all debris and previous cargo.
  2. The deck should be scrubbed and the bulkheads and deck wiped with a light disinfectant.
  3. All bilges must be cleaned and bilge suctions tested.
  4. ’Tween deck scuppers must be tested, together with all ‘U’ brine traps.
  5. Bilge plugs should be inspected and sealed. Cover plug over bilge suction may be left off for the purpose of survey.
  6. Fans must be checked for direction of air flow.
  7. Bare steelwork must be insulated.
  8. All odours must be cleared from the compartment.
  9. All outside ventilation must be shut down.
  10. Pre-cooling of the compartment must take place before the cargo is received, times being noted in the cargo log or deck log book.
  11. Before loading, the compartment should be surveyed.The surveyors’ comments together with the opening temperature of the chamber should be recorded in the mate’s deck log book.
Any dunnage required for the cargo should be of a similar standard of cleanliness as that of the compartment.All slings, chains etc. should also be clean and pre-cooled in advance of cargo reception.


Preparation of Spaces to Receive Cargo

The generally sensitive nature of refrigerated cargo requires very careful preparation of the space to receive it. Cleanliness is obviously of great importance particularly with foodstuffs. The space must be free of odours and micro-organisms and may require fumigation. The introduction of ozone will deal with airborne smells but, in extreme cases, lingering ones which have been absorbed by the insulation may require the removal and renewal of the affected portions. Fans should be run in both directions to clear smells and dust, etc., from the air trunking.

Bilges and scuppers must be clean, tested and U-bend vapour traps sealed with brine to prevent cross taint between compartments. Thermometers, gas sampling points, fire detection and extinguishing equipment should be carefully checked and inspected. Inspection should also be made of any pipes passing through the space, particularly their joints, for signs of leakage. Traditional timber dunnage is no longer used and reefer ships are fitted with large gratings bolted to the deck and folding `tween deck hatch covers. The gratings can be of timber, bamboo or aluminium construction while trials of plastic gratings have recently taken place. The gratings are of sufficient strength to support a forklift truck with a loaded pallet and damaged pieces should be replaced before loading begins.

Closing arrangements (weather and `tween deck covers) and access hatch plugs should also receive careful examination. The space can then be cooled down to slightly below the carrying temperature and held there for at least 24 hours to ensure that all the residual heat is removed from insulation and other fittings within the space. The air temperature will quickly rise when the compartment is opened for loading and every opportunity should be taken to run the fans during breaks in the loading operation.

Receiving Cargo

Cargo presented for carriage under refrigeration should be pre-cooled to the carrying temperature since normally the vessel or container is only provided with sufficient power to deal with heat leakage and the modest amount of heat generated by living cargoes. Thus, the prime consideration when receiving refrigerated cargo for carriage is to see that it is at the correct temperature. There is always the possibility of a slight rise in the temperature of the surface during transit which the ship can well take care of provided the internal bulk of the packages is at the correct temperature. Spear thermometers are available to determine this.

Chilled cargoes are of less concern in this respect, but owing to their more sensitive nature great care and inspection is called for during receiving and stowage.

Most fruit and vegetable cargoes will be presented pre-cooled but must be carefully examined for any warm or over-ripe fruit which should be rejected. The general condition should be noted and each space sealed as loading is completed and the carrying environment reached as soon as possible. If, as sometimes occurs, a fruit cargo is presented for loading at orchard temperature, the ship may have to undertake cooling to the carrying temperature. This must be requested by the shipper in writing, or the bill of lading claused accordingly. Once agreed, cooling must be carried out as quickly as possible although very rapid cooling cannot be carried out since the incoming cool air must not be at or below the freezing temperature of the fruit.

Maximum air circulation must be possible throughout the stow (with adequate intermediate dunnage and battens if required) to assist the cooling process. If the stow does not cover the whole deck, the air delivery outlets not covered must be temporarily blocked off to prevent short circuiting of the air flow.

Taint

Odour, either pleasant or obnoxious, is closely associated with taste and it is undesirable that even a pleasant smell should intrude into the one expected from a food or even completely overpower its own delicate flavour. It is in this connection with foodstuffs that taint is principally a problem. Some products produce strong odours in themselves­others may be particularly susceptible to and readily absorb foreign smells. Individual commodities should not be stowed together, even though they may require the same considerations of temperature and humidity. The separation of odious and sensitive cargoes into separate airtight compartments will, in most instances, solve this problem .

However, badly fitting access hatch plugs and fan spaces might allow for a certain degree of cross taint as indeed would common scupper systems not sealed with U-bends or traps filled with brine. Pipes passing through a cargo space present a particular hazard as a leaking oil pipe or tank sounding pipe may result in obnoxious fumes entering the space. Special care is required with living cargo when air changes are necessary to ensure that fresh air introduced is completely free of taint, similarly that the vented air expelled from a space is not drawn into a space where it might cause contamination. An odious cargo may well leave a tainted atmosphere behind after discharge, and a sensitive cargo should not be loaded or discharged through such a space until it has been fully ventilated and the odours removed.



Related articles :
  1. Carriage of Citrus fruits

    2. Small consignments of citrus are often carried as a mixed cargo in the same compartment. When this is done, a compromise carriage temperature of 6.5° to 8°C is recommended. However, the shippers' instructions must be complied with if they differ from this recommendation.....Read more

  2. Carriage of apples

    3. Apples should be carried in accordance with the general rules for fresh produce . They readily taint other cargo and should not be stowed in the same hold as meat or dairy produce.....Read more

  3. Carriage of bananas

    4. Bananas are usually packed in cartons ranging in weight from 11kg to 18kg, which are palletised and carried in temperature controlled holds or refrigerated containers. Palletisation has two main advantages over break-bulk carriage.....Read more

  4. Methods of refrigeration

    5. Refrigeration is essentially the removal of heat through the process of evaporation. We choose to refrigerate commodities such as fruits and vegetables because we want to prolong their “practical shelf life” – the time from harvest until the product loses its commercial value.
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  5. Reefer cargo stuffing

    6. it is essential that all products are treated correctly prior to stuffing. Even though the temperature, ventilation and humidity are all optimal during the entire voyage, products will only arrive in perfect condition if the pre-treatment has been performed correctly. Successful shipping begins at the product sourcing area.
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  6. Growing demand for container refrigeration

    7. On deck refrigerated containers are generally serviced by clip-on air cooled electric motor drive cooling units. The units are plugged into the ships electrical system by way of suitable deck sockets.
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  7. Frozen products packaging requirement

    8. Proper packaging procedures will help protect frozen cargo during transport. Frozen products do not require air holes in the top and bottom of the cartons. Air flowing around the load is sufficient to remove heat that has penetrated the container. The cartons should be stacked directly on top of each other to take advantage of their strength in the corners.
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  8. Carriage of beef

    9. Carried under temperature control, beef may be chilled or hard frozen; boneless or on the bone; bagged or cartoned......Read more

  9. Packaging & stowage guideline for reefer cargo

    10. Packaging plays an important role when it comes to protecting the cargo. The packaging material must be able to support a stacking height of up to 2.4 metres (7’10’’). The material should be able to withstand humidity without collapsing, and should allow the passage of an adequate vertical airflow through the cartons in order to maintain the desired temperature..
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  10. Choice of packaging for various commodities

    11. Goods should be well stowed within the package, evenly distributed and properly secured. Items completely filling the case or carton contribute to the strength of the whole package. Items which do not completely fill the package must be cushioned against shock or vibration.
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  11. How to keep cargo fresh ?

    12. Proper ventilation of fresh, chilled products is necessary to remove the heat, carbon dioxide and other gases produced by the cargo. Heat is removed by continuously circulating the internal air, whereas carbon dioxide and other gases are removed by replacing the internal air supply with cooled fresh air..
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  12. Loading precautions for refrigerated cargoes

    13. Refrigerated cargoes include meat carcases, carton (packed) meat, fruit, cheese, butter, fish and offal. Ships are specifically designed for their carriage, with separate spaces in holds and ’tween decks, each fitted with suitable insulation and individual control of ventilation. Ordinary general cargoes may be carried in the spaces at other times, the temperature being regulated accordingly for the type of cargo being carried.
    More .....




Summarized below various refrigeration system components, working process and maintenance guideline:
  1. Automatic direct expansion refrigeration- vapour compression

    2. The basic components of any refrigeration system (Figure 11.1) working on the vapour compression cycle, are the compressor, condenser, expansion valve, evaporator and the refrigerant fluid which is alternately vaporized and liquefied during the refrigeration cycle. The temperature at which a fluid boils or condenses, is known as the saturation temperature and varies with pressure....more

  2. Choice of refrigerants

    3. Theoretically, almost any liquid can be used as a refrigerant if its pressure/temperature relationship is suitable for the conditions. Although no perfect refrigerant is known, there are certain factors which determine a refrigerant's desirability for a particular duty and the one selected should possess as many as possible of the following characteristics.....more

  3. Refrigeration systems - Chamber cooling arrangements

    4. To avoid having an extended refrigeration circuit for cargo cooling, a brine system can be used. The brine is cooled by the evaporator and in turn cools grids or batteries. Grids provide cooling which relies on convection and conduction but air circulated through brine batteries provides a positive through cooling effect. .....more

  4. Refrigeration system components

    5. Marine condensers are generally of the shell and tube type, designed for high pressures. There may a few coil-in-casing or other types still in use. The coolant passes through the tubes with refrigerant condensing on the outside......more

  5. Refrigeration system compressors

    6. Refrigeration compressors are usually either reciprocating, or of the rotary screw displacement type. Centrifugal and rotary vane compressors have also been used.....more

  6. Refrigeration systems expansion valves

    7. The expansion valve is the regulator through which the refrigerant passes from the high pressure side of the system to the low pressure side. The pressure drop causes the evaporating temperature of the refrigerant to fall below that of the evaporator. .....more

  7. Monitoring instruments,CO2 measurement & Heat leakage and insulation test

    8. All necessary cargo temperature readings are obtained on modern reefers and container ships on a data logger which makes an automatic record. The temperatures and pressures relating to refrigerant gas and liquid, cooling water, brine and the ambient are also required. Most of these are obtained from direct reading instruments. .....more

  8. Marine condenser assembly

    9. The temperature of the refrigerated spaces with a direct expansion system is controlled between limits through a thermostatic switch and a solenoid valve which is either fully open to permit flow of refrigerant to the room evaporator, or closed to shut off flow. The solenoid valve is opened when the sleeve moving upwards due to the magnetic coil hits the valve spindle tee piece and taps the valve open.....more

  9. Comparison between refrigerants R717 ammonia & R744 carbon dioxide

    10. The ammonia used for refrigeration systems based on the use of a compressor, condenser, expansion valve and an evaporator (Figure 11.2) is dry (anhydrous) in that there is no water in solution with it. It has the chemical formula NH3 but as a refrigerant, it is coded with the number R717....more

  10. Container cooling system

    11. The air is cooled either by brine or direct expansion batteries and the containers are arranged so that one cooler can maintain a stack of containers at a given temperature. The temperature of the return air duct for each container is monitored.....more



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