Types of Freezing Equipment for Fishery Products

Freezing is the backbone of modern fish processing. Once a catch leaves the water, the clock starts ticking – bacterial activity accelerates, enzymes begin breaking down muscle tissue, and quality deteriorates fast. According to the FAO’s guide on freezing and refrigerated storage in fisheries, selecting the right freezer depends on three key factors: financial considerations, functional requirements, and operational feasibility. No single freezer fits every situation, which is why the industry has developed several distinct types of freezing equipment – each engineered for specific products, volumes, and quality goals. This post breaks down the major types of freezing equipment used for fishery products, how each one works, and what makes it suitable for different processing needs.

Why the type of freezer matters 🔗

Fish is composed of up to 80% water, making it highly vulnerable during the freezing process. When freezing is slow, large ice crystals form inside the cells, rupturing cell walls and causing irreversible damage to texture, moisture retention, and flavor. Rapid freezing, on the other hand, produces smaller ice crystals that cause far less structural damage, so the thawed product more closely resembles fresh fish in taste, color, and firmness. Choosing the right equipment ensures the fish reaches its target core temperature quickly, consistently, and with minimal product loss – all of which directly affect profitability and export quality.

Plate freezing 🔗

Plate freezing is a well-established method that maintains nutritional value and quality while delivering a long shelf life. It works through direct conduction – fish or packed fish products are placed between hollow metal plates, which are chilled internally by a refrigerant such as ammonia or CO₂. The plates are then closed together, applying gentle pressure and creating direct, full-surface contact with the product on both sides.

How it works 🔗

The hollow plates are chilled by refrigerants such as ammonia or Freon, arranged in parallel, and the seafood – typically packed in flat blocks or trays – is placed between them. The plates close together, applying gentle pressure and creating direct contact on both sides. This eliminates the need for circulating large volumes of cold air, making the process significantly more energy-efficient than blast-based systems. Plate freezing is up to 40% more energy efficient than traditional freezing methods.

Best suited for 🔗

The two main uses for horizontal plate freezers are the freezing of prepacked cartons of fish and fish products for retail sale, and the formation of homogeneous rectangular blocks of fish fillets – called laminated blocks – for the preparation of fish portions. They are also widely used onboard fishing vessels, where space is limited and compactness is critical. Products like shrimp blocks, fish fillets, squid, and surimi are particularly well-suited to this method.

Tunnel freezing 🔗

Tunnel freezing is one of the most widely used methods in industrial-scale fish processing. A tunnel freezer is an industrial device designed to freeze products quickly and evenly. It consists of a sealed chamber into which food products are placed, moving through the tunnel by means of a conveyor belt system. Inside the chamber, cold air currents are generated to freeze the food items in a very short time, ordinarily within minutes.

How it works 🔗

Fish is loaded onto a continuous conveyor belt that carries it through a long, insulated tunnel. Cold air, typically at temperatures between -30°C and -40°C, is circulated at high velocity over the fish as it moves through. The freezing tunnel operates using precision-engineered airflow systems that ensure even temperature distribution. Through directed cold air, quick-freezing temperatures are achieved, reducing the likelihood of ice crystal formation that can damage the product’s cellular structure.

Best suited for 🔗

Tunnel freezers offer high versatility – they can handle fish fillets, whole fish, and mixed seafood products of varying shapes and sizes. Their continuous-flow design makes them ideal for high-volume processing lines where throughput and consistency are priorities. Tunnel freezers are designed to freeze products rapidly and uniformly, ensuring quality preservation and shelf-life extension of food items such as meat, seafood, ready meals, and vegetables.

Spiral belt freezer 🔗

The spiral belt freezer is a space-saving solution built for continuous, high-capacity freezing. The outward appearance of the spiral freezer is that of a large square box. Inside, the belt spirals around a center drum, with each layer a few inches higher. The product is normally fed into the bottom of the spiral and exits at the top. This vertical arrangement allows a very long conveyor path – sometimes up to 450 feet of belt – to be contained within a compact footprint.

How it works 🔗

A spiral freezer uses a continuous belt wound vertically around a central drum. This design maintains consistent airflow and temperature across compact floor space, giving processors high capacity without expanding the building footprint. Cold air circulates uniformly through the spiral tiers, freezing the product evenly as it ascends. Many modern spiral systems include variable-frequency drives (VFDs) to control belt tension and speed, giving operators finer control over freezing curves and reducing surface dehydration.

Best suited for 🔗

Spiral belt freezers are well-suited for products that require gentle handling – such as breaded fish sticks, shrimp, fish fillets, and scallops. The Advanced IQF Spiral Freezer is a continuous in-line-belt freezer designed to minimize product weight loss and assure quality gentle handling during the freezing process, and is used for raw or breaded fish sticks or patties, shrimp, fish fillets, scallops, and whole fish.

Contact tunnel freezer 🔗

The contact tunnel freezer is a hybrid design that combines elements of both plate freezing and tunnel freezing into a single, efficient system. It is designed to deliver the speed benefits of direct contact freezing alongside the continuous-flow advantages of a tunnel setup.

How it works 🔗

Fish is placed on a conveyor belt that moves through a tunnel lined with refrigerated plates. Most contact plate freezers operate between -35°C and -45°C to achieve rapid and thorough freezing. The plates make direct contact with the underside of the product as it travels through, while cold air is simultaneously circulated within the tunnel to enhance the overall freezing rate. This dual mechanism – conduction from the plates and convection from the air – results in faster, more uniform freezing compared to either method alone.

Best suited for 🔗

The plate belt tunnel freezer is used to crust-freeze difficult-to-handle products, such as raw, marinated proteins, sauced foods, and semi-liquid products, forming a frozen crust that makes seafood portions easier to handle, allows for IQF since portions don’t freeze together, and increases yield by reducing moisture loss. It is particularly useful in processing lines that handle both delicate and semi-liquid seafood preparations.

Fluidized bed freezing 🔗

Fluidized bed freezing is the go-to method when the goal is Individual Quick Freezing (IQF) of small, loose seafood pieces. It produces a free-flowing frozen product where each piece remains completely separate – no clumping, no sticking.

How it works 🔗

A fluidized bed freezer uses upward-blown cold air to suspend and separate individual pieces as they freeze. The seafood floats lightly above a perforated conveyor belt while freezing air circulates from below. Because items stay in motion, no surface contact occurs, avoiding sticking or compression marks. Some advanced models also incorporate mechanical vibration of the belt to further prevent adhesion between pieces during the early stages of freezing. Most systems use a two-stage freezing sequence – a quick crust freeze, then deep freezing – to lock shape and prevent surface dehydration.

Best suited for 🔗

Small cooked and shelled shrimp is one of the few fish products that has been successfully frozen by the fluidized method. Beyond shrimp, this method works well for peeled scallops, diced fish, fish balls, small fillets, and fish mince portions – essentially any small, uniform seafood pieces that need to remain individually separated for convenience portioning and retail packaging.

Cryogenic freezing 🔗

Cryogenic freezing represents the most advanced and fastest freezing technology available in seafood processing today. Instead of mechanical refrigeration, it uses the direct application of cryogenic gases – typically liquid nitrogen (LN₂) at -196°C or liquid carbon dioxide (LCO₂) at -78.5°C – to achieve near-instant freezing.

How it works 🔗

Cryogenic tunnel freezers utilize cryogenic liquids – primarily liquid nitrogen or carbon dioxide – to achieve rapid freezing. As the cryogenic liquid comes into contact with the products, it rapidly absorbs heat, vaporizes, and freezes the products quickly. The fish is exposed to the cryogen inside a freezing chamber as it travels along a conveyor, and the entire freezing cycle can be completed in a matter of minutes. Modern cryogenic spiral systems further optimize efficiency: the two-stage freezer capitalizes on the BTUs available in the phase shift as liquid nitrogen transitions to gas, capturing and recycling cold gas from the immersion stage, making the process about 50% more efficient than with liquid nitrogen alone.

Best suited for 🔗

Cryogenic freezing is recommended for new production lines, seasonal production, or small and medium productions of high-quality food. The investment in a cryogenic freezing solution is 2.5 times lower than in a mechanical solution, with lower initial start-up costs, smaller dimensions, and the equipment is always ready to use and easy and fast to clean. It is particularly valued for high-quality, high-value seafood products – such as sashimi-grade fish, premium shrimp, and delicate fish fillets – where texture and appearance preservation are non-negotiable. The main trade-off is the ongoing operational cost of purchasing and storing cryogenic gases, which makes it less economical at very large, continuous production volumes compared to mechanical systems.

Comparing the six freezing systems 🔗

Each freezing technology occupies a specific niche in seafood processing. Plate freezers excel at block-frozen products and work well in space-constrained environments, including onboard vessels. Tunnel freezers handle the broadest range of product shapes and are the workhorses of large-scale continuous lines. Spiral belt freezers maximize throughput in limited floor space and are ideal for coated or delicate products. Contact tunnel freezers deliver the dual benefit of plate contact and air circulation, making them suitable for difficult-to-handle products. Fluidized bed freezers are the gold standard for IQF of small, loose seafood pieces. And cryogenic freezers offer unmatched freezing speed and quality for premium, high-value products – particularly where a low capital investment and fast setup time are required. The right technology choice is determined by product type, target capacity, packaging preference, and investment and operating costs. Often, a combination of multiple freezing methods in one facility gives the best result.

What do you think? Given that each freezing method has distinct advantages for different fishery products, how would you decide which system best fits a mid-scale coastal processing plant handling mixed catches? And do you think cryogenic freezing will eventually become the standard in the industry as equipment costs decline?

References

1. https://www.fao.org/4/v3630e/v3630e05.htm
2. https://klingecorp.com/blog/how-blast-freezing-improves-the-quality-of-fish/
3. https://rinac.com/blog/the-benefits-of-using-a-plate-freezer-for-freezing-fresh-produce-and-meats/
4. https://www.kelolalaut.com/details/articles/1731/freezing-seafood-with-contact-plate-freezers-process-benefits-and-best-practices
5. https://www.interlakemecalux.com/blog/tunnel-freezer
6. https://en.ntsquare.com/tunnel-freezer/benefits-and-applications-of-tunnel-freezer/
7. https://advancedfreezer.com/freezing-methods/
8. https://en.ntsquare.com/iqf/best-practices-for-seafood-processing/
9. https://advancedfreezer.com/seafood-industry-tunnel-freezers-spiral-freezers/
10. https://www.lindeus.com/industries/food-and-beverage/seafood/freezing
11. https://en.ntsquare.com/iqf/how-to-process-iqf-fish/
12. https://www.messer-us.com/food-freezing
13. https://dsidantech.com/products/tunnel-freezer-cryogenic
14. https://www.frigomekanik.com/en/blog/seafood-refrigeration-systems-best-practices-in-fish-processing-and-storage