Keeping Fish Cold
August 1, 2019
Part three in a 3-part series about extending shelf life through Good Manufacturing practices.
Unless you are transporting live product or are freezing on board, all fisheries, all gear types, all vessels have one thing in common – the product must be chilled. Refrigerated temperatures help slow or stop the growth of harmful bacteria and the cellular breakdown of tissue. The methods for keeping fish cold; RSW, layer ice and slush ice all come with their own pros and cons. The formula for achieving cold is further complicated by the different kinds/temperatures of ice and the product being chilled.
Most of the ice available on the West Coast and Alaska comes from the workhorse of icemakers, Norstar. An ice salt mixture is sprayed on the inside of a drum. A rake circles the drum breaking the ice off. The ice falls into a containment unit below the ice maker in large flakes. The ice is made with a slight salt additive, allowing it to reach temperatures below 32 degrees. Another frequently used flake ice maker is the Morris – which uses a series of cylinders that go through freeze and defrost cycles to make and shed the ice. The ice does not get as cold as Norstar ice but does break apart easily after being stored.
Flake ice is used to layer ice products in hold and in totes.
The table (below left) shows the weight of ice necessary to cool 10 kg (22 pounds) of fish to 0 °C /32F from various ambient temperatures. A rule of thumb for quick cooling while layer icing is a ratio of 1 to 3 ice to fish.
Flake ice can also be used to create an ice slurry. The benefit of slurry is that the chilling properties of the ice are spread more thoroughly throughout the load, resulting in even and consistent chilling. If creating an ice slurry with flake ice, it is very important that correct ratios are observed. The water-to-ice ratio needs to create a thick enough slurry that fish are suspended in the slush. If there is too much water to ice, the flake ice will act like sandpaper and abrade the skin of the fish, resulting in a loss of quality. If too little water to ice, the ice will set hard and freeze in large clumps, also causing damage to the fish. Perfecting the use of slush ice can take some time and practice but when done right, is better than layer icing at preserving overall quality and rapid chilling.
There is some discussion over the effectiveness of adding salt to a slush ice mix. Slush ice made with a salt base ice or where additional salt has been added to the mixture, can result in fish that are delivered partially frozen. While hardier species such as round sablefish and pacific cod can hold up to these temperatures, irreparable damage can be done to the more delicate flesh of salmon, and salmon roe can be rendered unusable by the partial freezing. Slush ice is also not appropriate for gutted fish such as halibut. Some plants have gone to using technology like Sunwell to provide a ready to use ice slurry. These slurries have had mixed reviews from users and have yet to make major headway in harvester icing.
Vessels equipped with RSW may choose to add ice to the tanks in order to make chilling more efficient. Used alone, or with ice, RSW is most efficient when the water is prechilled. The tank should be filled half full with water and the refrigeration cycle started early enough that the water temperature will be at or close to 32 degrees before fish is added. Most fish are cold blooded and will come aboard the vessel at the ambient temperature of the surrounding water. Immediately submerging them in 32-degree water ensures the chilling process and slows the degradation of quality.
Chilling seafood is the single most important factor in the quality and shelf life of the product. Fishermen have a larger impact on the final quality and customer perception of their product that any other hand that touches the product along the supply chain. Every time a salmon is dry picked, the fish are left on the sorting table or the halibut lie on deck waiting to be dressed, quality is rapidly reduced. Do your part – keep it cold, keep it moving.
Brandii (O'Reagan) Holmdahl is the Director of Quality and Regulatory Compliance with Bornstein Seafoods. Over the last 28 years she has worked in seafood production in every major region and handling most species of seafood harvested in Alaska. She has also fished on long liners, gill netters and worked on tenders. She recently spent 2 years in global seafood exports and imports on the East Coast and has returned to the Pacific Northwest to follow her passion for helping fishermen deliver the highest quality seafood available.