Fresh HOG (head-on gutted) salmon loaded in an insulated Twin Tub for transport. Proper chilling methods ensure the fish arrive in prime condition with minimal weight loss.
Introduction – The Need for Optimal Cooling in Salmon Transport
Transporting farmed salmon from harvest to processing requires maintaining peak freshness and quality over several days. Rapid chilling immediately after harvest is critical to slow spoilage and preserve fish texture and moisture[1]. Traditionally, salmon are layered in boxes with flake ice to keep them cold. However, new “superchilling” techniques allow fish to be cooled just below 0 °C (without fully freezing) for even better quality retention[2]. In fact, superchilled salmon holds its water content better and stays firmer, extending shelf-life by up to a week compared to conventionally chilled fish[3]. This has opened the door to using durable Twin Tubs (reusable insulated bulk containers) instead of disposable boxes for salmon transport. Historically it was “not advisable to transport whole salmon iced in tubs, as the ice can damage the fish,” but with superchilling the best quality can be achieved using tubs[4]. Below we explore two state-of-the-art cooling methods – flake ice pre-chilling and slurry ice chilling – that companies like iTUB employ to ensure salmon reach the processor in top condition. Each method has distinct advantages backed by industry research, underscoring iTUB’s focus on quality and leadership in innovative seafood packaging.
Method 1: Superchilling with Flake Ice (Pre-Chilling the Salmon)
Flake ice is the most traditional cooling medium in the seafood industry. It consists of flat, thin “chips” of ice that are applied by shoveling over the fish[5]. Flake ice is popular because it’s simple and inexpensive[6]. However, its larger particles have relatively low surface area and can cool unevenly, leaving air gaps. The hard, sharp edges of flake ice can also be abrasive – causing bruises or scratches on delicate fish if not handled carefully[5].
Despite these drawbacks, flake ice can be used in an advanced way to superchill salmon. In this approach, freshly harvested salmon are first pre-chilled to just below 0 °C (around -0.5 to -1.0 °C) using flake ice under controlled conditions. This superchilling essentially turns the fish into its own cooling reservoir, since a portion of the water in the fish flesh is almost frozen[2]. The fish muscle, which is ~70% water, can thus hold a cold temperature longer without needing as much external ice[7]. Once the salmon are thoroughly superchilled, they are loaded into insulated Twin Tubs for transport – typically about 190–220 kg of HOG salmon per tub with only ~10–20 kg of flake ice added for the journey[8]. Because the fish were cooled below the freezing point of plain ice, only a small buffer of ice is needed to maintain temperature. The cooling is “locked into” the salmon’s flesh, keeping core temperatures around -0.5 °C for the duration of transit.
Research and results: Superchilling with flake ice (or similar methods like refrigerated seawater) has proven highly effective. Extensive Nordic studies led by Matís (Iceland’s food research institute) found that superchilled salmon “holds its water content better” during processing, with minimal drip loss and firmer fillet texture over time[3]. The fish stay out of the rapid decay zone – onset of rigor is delayed and muscle fibers retain integrity, leading to less gaping and a higher fillet yield[9][3]. Shelf-life trials confirmed superchilled salmon remains sensorially fresher and can extend the shelf life by as much as a week beyond conventionally iced fish[3]. In practical terms, this means salmon harvested in Iceland, superchilled with flake ice, and shipped to continental Europe (a 4–6 day trip) arrive with excellent quality and minimal drip loss. Indeed, field tests by iTUB with Dutch processor Adri & Zoon and Arctic Fish in Iceland showed no drop in quality when using Twin Tubs versus the standard EPS ice boxes – in fact, fillet yields even improved in some cases[10]. Superchilling essentially mitigates the usual transport damage: the fish are firmer and protected from bouncing against hard ice, since only a thin layer of flake ice surrounds them. This method demonstrates that, with the right preparation, transporting salmon with very little ice is not only possible but beneficial.
Method 2: Rapid Chilling with Slurry Ice (Ice-Water “Slush”)
An alternative cutting-edge approach is using slurry ice to cool and transport the salmon. Slurry ice is a mixture of countless small ice crystals (typically 0.1–1 mm) suspended in water or brine, forming a pourable “slush” that can surround the product completely[11]. In practice, salmon are loaded into the Twin Tub (usually ~150–200 kg of fish per tub), then this liquid ice slurry is pumped in around them (e.g. 50–100 kg of slurry). The fluid ice fills all voids around the fish, ensuring 100% contact with the salmon’s surface for uniform cooling[11]. Within about 15–20 minutes of immersion, the fish core temperature drops rapidly to roughly -0.5 °C. At that point, the excess ice-water is drained off through special outlet plugs in the tub, leaving the fish surrounded by a thin layer of residual ice. The salmon, now thoroughly chilled and at an optimal sub-zero holding temperature, remain in the tub (without sloshing water) for the journey, which can be up to several days.
Advantages of slurry ice: This method offers several clear benefits. First, cooling is extremely fast – studies show slurry ice can chill seafood about three times faster than flake ice can[12]. The fine ice crystals and liquid medium provide a far greater heat transfer surface area, pulling heat out of the fish very efficiently. In one report, slurry ice chilled fish to 0 °C in only ~12–14 minutes, whereas conventional ice took significantly longer[12]. Moreover, because a slurry can be made with saltwater, it stays fluid and can cool below 0 °C (commonly maintaining fish at -0.5 to -1.0 °C), a temperature that pure flake ice cannot achieve[13]. This means slurry ice has a stronger cooling capacity and keeps the fish in that superchilled state throughout transport. Second, slurry ice is gentler on the product. The micro-crystals have a smooth, gel-like texture and do not have sharp edges, greatly reducing surface damage to the fish[11]. Fish in slurry are essentially cushioned by the ice-water mixture, avoiding the bruising and compression that can happen with hard ice chunks and heavy layering. The slurry also prevents dehydration of the fish by completely enveloping it and excluding air contact[11]. Once chilled, the fish’s surface is coated in ice crystals that protect it from oxygen and moisture loss until processing[11]. A final practical advantage is improved handling and labor efficiency – slurry ice can be pumped in and out of containers automatically, eliminating the manual shoveling of flake ice[14]. This not only saves labor but ensures consistent icing of every fish. For example, a Canadian mussel processor switched from hand-applying flake ice to pumped slurry and noted that the slurry flowed “in between every mussel…ensuring fast cooling of the entire product,” and their customers reported much longer shelf life, “not wishing to go back to flake ice.”[15]
Quality and shelf-life outcomes: The slurry ice method has demonstrated impressive results in both research and commercial settings. Because it chills fish so rapidly and uniformly, spoilage bacteria are knocked down early, and the fish stays in the safest temperature zone. Scientific studies have found that using slurry ice during harvesting and transport can significantly extend the shelf life of fresh fish. For instance, a recent experiment on gilthead sea bream showed that partially replacing flake ice with slurry ice (50/50) improved the fish’s quality and extended shelf-life by 2–7 days at 0 °C storage compared to flake ice alone[16]. Similarly, trials on European sea bass and other species report that slurry-iced fish maintain better freshness and have lower microbial growth, gaining a couple extra days of acceptable shelf life over traditionally iced fish[17][16]. The superior temperature control is a key factor – by quickly bringing the fish into a subzero, near-frozen state, slurry ice dramatically slows down bacterial activity and enzymatic breakdown[18]. In practical terms, seafood shipped with slurry chilling often arrives with noticeably less drip loss (water weeping from the fish) and firmer texture. Processors have observed that slurry-chilled salmon fillets yield more, as less fluid is lost. Indeed, one seafood plant manager noted that customers could get 10–12 days shelf life with their shellfish packed in slurry ice, versus only ~7 days from a competitor using flake ice[19]. This aligns with lab findings that slurry ice preserves water-holding capacity in the flesh better than flake ice. Even when slight uptake of water or salt from a brine slurry occurs, studies indicate the fish can have higher water retention (WHC) and lower drip upon subsequent storage[20]. In one recent Norwegian study, salmon stored for 7 days in refrigerated seawater (-1 °C slurry) showed improved sensory shelf life and remained in excellent condition, whereas traditionally iced salmon had more drip and shorter shelf life[21]. The bottom line is that slurry ice achieves the same goal as flake superchilling – keeping fish at ~ -1 °C – but does it rapidly and thoroughly, leading to consistently high quality after days of transit.
Leadership in Quality – iTUB’s Salmon Solution
Both cooling methods described (flake ice superchilling and slurry ice chilling) represent the forefront of salmon transport technology, and iTUB’s Twin Tubs are specifically designed to leverage these techniques. Each Twin Tub is a robust, insulated container that can maintain sub-zero fish temperatures for days. They are built with drainage capabilities to handle slurry ice use (allowing melt-water to be removed easily), and they accommodate ~200 kg of salmon plus the necessary ice – roughly 10–20 kg of flake ice or 30–40 kg of slurry ice, depending on the chosen method[8]. By using superchilling, iTUB enables clients to drastically reduce the amount of ice shipped with the fish, which improves logistics and sustainability. (Traditionally up to 20% of the gross transport weight of salmon shipments was just ice[22] – weight that superchilling can largely eliminate.) The Twin Tubs keep the fish cold and protected without the mess of melting ice or risk of ice abrasion damage. This innovative system – dubbed the “Salmon Solution” by iTUB – is showing the industry that quality and sustainability go hand-in-hand.
iTUB backs these solutions with ongoing research and real-world validation. By collaborating with salmon producers and processors, iTUB has demonstrated that using Twin Tubs with either flake or slurry ice cooling yields equal or better product quality compared to the old model of polystyrene (EPS) boxes. As mentioned, trials saw no loss in fish quality versus EPS box shipments, and even an improvement in fillet yield in some cases[10]. This gives salmon exporters confidence that switching to this modern approach won’t compromise their product – on the contrary, it can enhance quality while also cutting down on packaging waste and carbon footprint. With superchilled transport, salmon can be sent longer distances (even by sea freight instead of air) thanks to the extended freshness window[23][22]. In short, iTUB has positioned itself as a leader in not just packaging, but in the science of cold-chain management for seafood. The company’s focus on research-driven solutions – from optimizing ice formulas to perfecting tub insulation – ensures that customers are using the best available technology to preserve fish quality.
Conclusion
Shipping salmon from farm to processor in peak condition is both an art and a science. The two methods outlined – flake ice superchilling and slurry ice cooling – are powerful tools that allow salmon to be transported for 4–6 days (or more) with negligible loss in quality, appearance, or weight. Flake ice, when used to pre-chill fish to around -1 °C, minimizes the need for added ice and keeps the fish firm and cold from the inside out. Slurry ice, with its rapid and uniform chilling action, achieves the same low temperatures in a very short time and protects the fish like a cold blanket. Research and industry experience concur that both approaches significantly reduce spoilage, maintain higher water content in the fillet, and extend the shelf life of the product[16][3]. By championing these techniques, iTUB underscores its commitment to quality and innovation. The Twin Tub system provides the practical means to execute flake or slurry cooling in the field, and iTUB’s team continues to refine these methods for even better results. In a market that demands not only freshness but also sustainability, iTUB’s holistic approach – investing in both advanced packaging and the science of fish preservation – sets it apart as an industry leader. Processors and buyers can be confident that, with the right cooling strategy and the right container, salmon can journey from fjord to factory with fresh-from-the-water quality, ensuring a superior product and higher customer satisfaction on arrival.
References (Research & Sources)
- Ming-Jian Wang. “Seafood Chilling, Preservation with Ice Slurry.” Global Seafood Alliance Advocate. (2010): Describes the rapid cooling and quality benefits of slurry ice for various seafood, including extended shelf life and reduced labor[14][19].
- NanoICE Blog. “Flake Ice, Slurry Ice or nanoICE: How to Choose the Best Fit.” (2020): Compares flake vs. slurry ice, noting flake ice’s uneven cooling and bruising potential, versus slurry’s uniform contact and gentleness[5][24].
- Athina Ntzimani et al. “Effect of Slurry Ice during Transportation on Quality and Shelf Life of Sea Bream.” Journal of Marine Science and Engineering 10(3):443 (2022): Found that partial use of slurry ice improved fish quality and added 2–7 days of shelf life at 0 °C vs. flake ice alone[16]. Also summarized slurry ice advantages: faster chilling (~3×), full surface coverage, less damage, and ability to chill below 0 °C[11][12].
- Sherry S. Chan et al. “Sub-chilling of Atlantic Salmon in -1 °C Refrigerated Seawater and Subsequent Storage.” Reports 15, 09371 (July 2025): Demonstrated that salmon stored in sub-zero slurry (RSW) for 7 days had higher water retention and longer shelf life than ice-stored salmon, highlighting superchilling’s effectiveness[21].
- Nordic Innovation & Matís. “Superchilling of Fish.” Project Summary (2016): Reported that superchilled Atlantic salmon (cooled to ~-1 °C) held moisture better, stayed firmer, and lasted ~1 week longer than conventionally chilled fish[3]. Noted that earlier, transporting salmon in tubs with ice was avoided due to damage risk, but superchilling allows safe tub transport with best quality[4].
- iTUB Rental – Salmon Solution FAQ (2025): Provides specifications of Twin Tubs and results from field tests. Confirms each tub carries ~200 kg salmon with 10–40 kg ice (flake or slurry)[8], and reports no quality difference in tub-transported salmon vs. EPS boxes in trials (with some improved fillet yields)[10].
[1] [14] [15] [19] Seafood chilling, preservation with ice slurry – Responsible Seafood Advocate
https://www.globalseafood.org/advocate/seafood-chilling-preservation-ice-slurry/
[2] [3] [4] [7] [9] [22] [23] Superchilling of Fish | Nordic Innovation
https://www.nordicinnovation.org/programs/superchilling-fish
[5] [6] [24] Flake ice, slurry ice or nanoICE: how to choose the best fit for you | nanoICE
https://nanoiceglobal.com/flake-ice-slurry-ice-or-nanoice-how-to-choose-the-best-fit-for-you/
[8] [10] Salmon | iTUB | Rental | Pooling
https://itub-rental.com/salmon/
[11] [12] [13] [16] [18] Seasonal Pattern of the Effect of Slurry Ice during Catching and Transportation on Quality and Shelf Life of Gilthead Sea Bream
https://www.mdpi.com/2077-1312/10/3/443
[17] Comparison of effects of slurry ice and flake ice pretreatments on the …
https://www.sciencedirect.com/science/article/pii/S0308814607002324
[20] [21] (PDF) Sub-chilling methods for Atlantic salmon with 7 days in refrigerated seawater and subsequent sub-chilled storage
