Proper on-board handling of fish contributes significantly to higher quality and longer shelf life
This article was featured in Eurofish Magazine 3 2021.
Fish from the Icelandic fishing industry has an enviable reputation for quality. Insulated containers have contributed to this in no small measure.
Onboard handling refers to the conditions that fish are subjected to after harvest and up to the point of landing, when the fish is transferred on shore, according to the FAO. Proper handling is critical to slowing the process of deterioration, prolonging the shelf life, and maintaining the quality of the product. Better handling increases thereby the value of the catch. At a webinar organised by Seafood Source, Björn Margeirsson Research Manager at Sæplast and Associate Professor at the University of Iceland spoke about ways in which on-board handling could be improved to maximise the value of the catch. As he pointed out, the quality of the fish when it leaves the sea is at its peak—from that point on the quality will only deteriorate. Therefore, the main aim of on-board handling and storage is to reduce this deterioration for as long and as effectively as possible. Chilling and the maintenance of good hygiene conditions are critical for quality and shelf life during fish handling.
Improvements have come about in a series of small steps
Iceland has a well-deserved reputation for exporting high quality fish. This has come about through investments in research and in developing technology which has led to incremental improvements over a period of decades. Up to around 1970, fish was stored in bulk on shelves in the hold. Thereafter, shallow plastic crates were brought into use. These were much better but there was a tendency to overload them with fish and ice resulting in high pressure on the crates at the bottom of the hold. Plastic crates were replaced by insulated plastic containers in the 80s and 90s. These were much better at maintaining the temperature, but initial generations of these insulated tubs were so big and deep (660 litres with a depth of 58-60 cm) that the fish at the bottom of the tub was subject to sub-optimal pressure from the layers above. From the mid-90s these tubs were replaced by shallower insulated containers that typically had a depth of 40-42 cm and a volume of 460 litres, resulting in a weight loss of around 1.5% compared to around 2% for the 660-L tubs during one-week storage. The 460-L containers have since become the most widely used containers for fish in the Icelandic fresh fish industry. The holds in modern vessels in Iceland house rows of neatly stacked containers of this type and are often equipped with automatic systems for moving them around.
Bleeding and chilling determine fillet quality
On-board handling starts with the catch arriving on board followed by, in some instances, sorting by size and species. Mixing red fish with cod or haddock, for example, may have an impact on the quality of the latter, so it is better to sort them. Bleeding is the next stage and it is important to remove the enzymes and iron present in the blood which can otherwise compromise quality and affect fillet appearance. This step together with chilling are the most important determinants of fillet quality, emphasised Mr Margeirsson. Bleeding carried out within 30 minutes of capture gives the best results in terms of fillet colour. After that, the longer the interval before being bled, the more discoloured the fillet. Bleeding is followed by gutting which removes microbes from the fish and thus also helps to preserve quality. However, Mr Margeirsson said, experience in Iceland had shown that if proper washing is not possible post gutting, then it was probably better not to gut the fish on board but to do it later onshore. This is normal practice in Iceland for fishing trips shorter than a day, but on longer trips, which are common, the fish will be gutted and thoroughly washed on board. After washing, the fish must be chilled, a process that entails first bringing the temperature down to 0 or -1 centigrade and then maintaining this temperature while the fish is under storage. The quicker the fish is brought to this temperature the longer the shelf life. Chilling can be achieved with different media—brine, ice of different kinds, or refrigerated seawater. Following chilling the fish must be packed in boxes with ice. Research has shown that cod stored at zero degrees has a shelf life of 12-15 days while storing at 10 degrees centigrade reduces shelf life to three-four days. The longest possible shelf life is of the utmost importance when the fish is 5-6 days away from the market where it will be sold. Until 2005 or so it was customary to chill to 0 degrees centigrade, but then it was discovered that superchilling to minus 1 degree centigrade can increase the shelf life by 1-3 days (as compared to the 12-15 days at 0 °C).
Each form of ice has benefits and disadvantages
The fisheries sector uses different kinds of ice to chill and store the fish including block ice, flake ice, crushed block ice, and slurry ice. Ice is used to reduce the temperature and, as it melts, to keep the fish clean and moist. Slurry ice, a pumpable mixture of ice, water, and salt, can be cooled to minus 2 or minus 3 centigrade. It chills therefore faster than flake ice, which has a melting temperature of about 0 degrees. The small particles of ice in the slurry are also gentler on the fish than the sharp edges of flake ice. Another advantage is that since it encloses the fish better without air gaps at the fish surface, the transfer of heat from the fish to the cooling medium is higher. Rapid chilling postpones rigor and maximises its duration thereby reducing the risk of toughness, gaping, and shrinkage in the fillet. However, temperature is only one factor influencing the impact of rigor. In general, there is no question that slurry ice works better if the main aim is to chill the catch fast, said Mr Margeirsson. Maintaining temperature, however, is something else. Slurry ice is not as effective for this task because it actually has a lower cooling capacity per kilogram than flake ice. After the first few days of storage, the faster melting of the slurry results in inferior cooling capacity compared with flake ice. Therefore, a few shovels of flake ice are sometimes added on top of fish, which has been stored in slurry ice for a few days.
Insulated containers require less ice than single-walled ones
In Iceland recommendations for packing fish in flake ice are to start with a layer of ice, followed by a layer of fish, bellies down to prevent water from accumulating in the gut cavity. Successive layers of ice and fish follow terminating in a top layer of ice after which the lid is put on. The drain holes in the container are kept open to allow melt water to escape. The accumulation of melt water is detrimental to quality. Mr Margeirsson also showed that fish arranged in two layers in a container can take 9-12 hours to cool from 10 to 2 degrees C, while if arranged in three layers the same reduction in temperature would take 4-5 hours. Insulated containers offer an advantage when storing the fish at these temperatures as they maintain the ice much longer than single walled containers. As a result, less ice is needed to keep the fish cool, though this is also influenced
by how well the hold is refrigerated. The final stage of the handling on board is when the containers are offloaded and transported to the processing facility or auction. Offloading highlights another difference between plastic crates and insulated containers that has implication both for speed and for safety when offloading. A catch of 100 tonnes of gutted fresh fish could take 8 workers up to 8 hours to offload when using fish crates. With 460 litre insulated containers the same volume could be offloaded in 3-4 hours by two people. However, the faster offloading presupposes the use of heavier equipment such as cranes.
In conclusion, Mr Margeirsson told the audience that insulated containers and ice will increase quality, reduce handling, extend shelf life, and maximise yield. They are quicker and safer to offload, and the fish will command higher prices. In the Icelandic fishing sector, constantly optimising on-board handling has contributed to an increase in the value of catches over the years.