The core of aquatic product quick-freezing is not “bringing the temperature down,” but passing through the ice crystal formation zone (0℃ to -5℃) as quickly as possible: the faster it passes, the finer the ice crystals inside the cells, and the less drip loss after thawing. Thin materials such as shrimp and fish fillets, and thick materials such as whole fish and squid tubes, do not follow the same equipment route.
TL;DR
- Materials that are thin and require individuation (shrimp, fish fillets, squid rings) go through a liquid nitrogen tunnel, with variable-frequency mesh belt speed control and high degrees of individuation.
- Continuous large-batch lines with relatively fixed categories go through an immersion chiller, where the heat exchange medium contacts the material directly, with throughput up to ton-level per hour.
- Factories with multiple varieties, small batches, and fluctuating orders are equipped with blast freezers, handling tens to hundreds of kilograms per batch, with no line changes needed when switching products.
- The common red line for all three routes: discharge core temperature ≤ -18℃, and the quick-freezing stage must let the material pass through the ice crystal formation zone (-1℃ to -5℃) within 30 minutes.
I. Three Difficulties of Aquatic Materials
High moisture content, soft tissue. The moisture content of shrimp is usually above 75%. If the freezing speed is insufficient, large ice crystals will pierce the cells, and water will come out at a press after thawing, with both weight and texture dropping.
Irregular shapes, prone to sticking. Shrimp, squid rings, and fish fillets stacked together will freeze into blocks, and must be broken apart during portioning, increasing the breakage rate. Individually quick frozen (IQF) requires that materials do not contact each other during freezing, or can be easily separated after contact.
Salt and protein are corrosive to equipment. Seawater residue, fish blood, and shrimp shell fragments adhere to the mesh belt and cabinet. If not cleaned thoroughly, scale and odors will accumulate, affecting the next batch of product.
These three points determine that equipment selection cannot look only at capacity figures, but also at how the material travels through the equipment, how it is separated, and how it is washed.
II. How to Choose Among the Three Equipment Routes
| Material form | Recommended equipment | Processing method | Applicable capacity |
|---|---|---|---|
| Shrimp, fish fillets, squid rings (thin, require individuation) | Liquid nitrogen quick-freezing tunnel | Mesh belt conveying, liquid nitrogen spray/immersion, variable-frequency speed control | Small-to-medium batch continuous production, one category per line |
| Whole fish, fish blocks, shellfish, prepared aquatic products (continuous large batch) | Immersion chiller | Mesh belt immersed in food-grade freezing liquid, liquid temperature down to -50℃ | Ton-level per hour, fixed category per line |
| Multiple varieties small batch, samples, seasonal orders | Blast freezer | Cart/tray in and out, batch freezing | Tens to hundreds of kilograms per batch |
2.1 Liquid Nitrogen Tunnel: The Mainstay for Thin Materials
The heat exchange efficiency of the liquid nitrogen tunnel comes from the temperature difference: the boiling point of liquid nitrogen is -196℃, the material surface instantly enters the deep low-temperature zone, and the time to pass through the ice crystal formation zone is compressed to a very short period. Structurally, the equipment is a SUS304 mesh belt passing through an insulated tunnel, with variable-frequency adjustable belt speed, and the material laid in a single layer or thin layer passing through.
Several key dimensions of the Kunning Cryo DKN-LFT series tunnel lines for reference: LFT-1206 mesh belt 6000 mm × 1200 mm, total power 9 kW; LFT-1212 mesh belt 12000 mm × 1200 mm, total power 18 kW, freezing capacity 1 m³/hour; LFT-1612 mesh belt effective width 1600 mm, suitable for wider material spreading. For a specific production line, the belt length must be back-calculated according to material thickness, inlet temperature, and target core temperature, and models cannot be copied directly.
The operating cost of the liquid nitrogen tunnel mainly falls on liquid nitrogen consumption, so whether the material spreading thickness and pre-cooling before feeding are done well directly determines the nitrogen consumption per kilogram of product. This part is broken down in How to Calculate Liquid Nitrogen Consumption.
2.2 Immersion Type: The Choice for Continuous Large Batches
The immersion chiller sends the material directly into the low-temperature freezing liquid. The heat transfer coefficient of liquid is much higher than that of cold air, and at the same temperature difference the heat exchange is faster. Moreover, all sides of the material contact simultaneously, so there is no situation where “the windward side is frozen while the back is still soft.”
Taking DKN-RHV-2000L as an example: tunnel inner box 23260 × 2360 × 570 mm, mesh belt effective width 2000 mm, freezing liquid temperature down to -50℃, working temperature ≤ -35℃, temperature control accuracy ±2℃, freezing capacity 0~2000 kg/hour, tunnel cycle time adjustable from 20~100 minutes, power supply 380V/50Hz, total power 320 kW, operating power about 270 kW.
Two points to note. First, the freezing liquid must be food-grade and able to contact food directly, and concentration and microbiological monitoring must be done daily. Second, the discharge end must have air knives for drying and freezing liquid recovery; otherwise the liquid is carried out by the material, which both increases consumables and affects packaging. The air knives and recovery device at the tail of the equipment are designed for this.
2.3 Blast Freezer: The Fallback When Orders Are Unstable
The value of the cabinet type is not in efficiency but in flexibility. A cabinet can freeze shrimp today and squid tomorrow; switching products only requires changing trays and parameters, without cleaning the whole line. It is suitable for samples, seasonal high-value-added categories, or as backup capacity when the tunnel line is under maintenance.
III. Two Examples of Line Configuration
Case 1: An export processing plant handling 10 tons of shrimp per day. The front section is washing, shelling, and grading. The quick-freezing section uses a liquid nitrogen tunnel, with the material laid in a single layer on the mesh belt. Before feeding, pre-cooling reduces the product temperature from 15℃ to about 5℃, reducing the sensible heat load in the tunnel. After discharge, it goes directly to a -18℃ cold storage or packaging room. The bottleneck of this line is usually in grading and packaging, not in quick-freezing itself.
Case 2: A continuous line for prepared aquatic products (breaded fish steaks, seasoned squid). The material carries a batter coating, which is prone to drying and sticking; the immersion type is more stable: liquid heat exchange does not blow air, so the coating is not blown off, and the mesh belt hold-down belt keeps the material fully immersed. The disadvantage is that a line is basically locked to one category, and switching products requires thorough cleaning of the freezing liquid system.
The logic of configuration is: first determine the category and daily capacity, then determine the equipment form, then calculate power and footprint. Conversely, looking at equipment parameters first to match a production line will most likely lead to losses in cleaning and product switching.
IV. What to Look at During Acceptance
- Core temperature: Immediately after discharge, use a probe to measure the thickest core part, ≤ -18℃; sample no fewer than 3 points (inlet end, middle section, discharge end).
- Time to pass through the ice crystal zone: Control the time from 0℃ to -5℃ within 30 minutes; this is the dividing line between quick-freezing and slow-freezing.
- Moisture loss rate: Compare weights before and after freezing. Thin materials are usually required to be controlled at a low level; if the agreed value is exceeded, check whether the air speed, material spreading thickness, and pre-cooling are in place.
- Cleaning accessibility: Mesh belt, cabinet inner walls, freezing liquid tank, and air knives—all four locations must be removable and flushable. The Kunning Cryo tunnel line adopts an integral lifting structure, allowing the mesh belt to be raised as a whole for 360-degree cleaning, and the cabinet bottom has a shallow V-shape with a drain outlet.
- Freezing liquid status: Concentration, turbidity, and microorganisms—all three must have daily records.
V. Frequently Asked Questions
Q: Between the liquid nitrogen tunnel and the immersion type, which has lower operating cost? A: It depends on electricity price and liquid nitrogen price. Liquid nitrogen is priced by the kilogram and follows the market, while the immersion type consumes electricity but the electricity price is relatively stable. For daily capacity above ton-level with fixed categories, the unit cost of the immersion type is usually more controllable; for daily output of hundreds of kilograms with frequent category changes, the liquid nitrogen tunnel is easier to start and switch. The specific calculation must be based on local electricity prices and liquid nitrogen quotations; we can provide a comparison after obtaining these two figures.
Q: Must shrimp be individually quick frozen? A: Export and domestic portioning requirements differ. To do IQF, the material must not be stacked during freezing, and the tunnel material spreading thickness and mesh belt speed must match; if it will later be cut into blocks or minced, block freezing is also acceptable, and then the equipment choices are much broader.
Q: Can the equipment adapt to 60Hz power supply? A: Yes. 380V/50Hz is the standard configuration. For export to 60Hz regions (such as Mexico 440V/60Hz, Peru, etc.), motors and control components need to be re-selected according to the order, and both quotation and delivery time will change. The destination power grid should be provided together during selection.
Q: Can one line freeze both shrimp and fish fillets at the same time? A: Yes, but the time cost of parameter switching must be accepted. Switching categories on a tunnel line requires changing mesh belt speed, liquid nitrogen flow, and cleaning the mesh belt; switching on the immersion type requires evaluating whether the freezing liquid needs to be replaced. For factories with a large category span, equipping a main line plus a cabinet machine is often more practical than forcing one line to handle everything.
Q: How many times a day should cleaning be done? A: Follow the production batches. Protein and salt residues from aquatic products are prone to breeding bacteria; usually a rinse at the end of each shift and a complete cleaning once a day. Whether the equipment is easy to disassemble and wash affects actual output more than the nominal capacity in the long run.
VI. Next Steps
If you are planning an aquatic product quick-freezing line, send us these items: category and form, unit weight and thickness, daily capacity or hourly capacity, inlet temperature, target core temperature, destination power grid, existing upstream and downstream equipment. Engineers will provide equipment form recommendations and capacity calculations based on these parameters; parts with incomplete parameters will be confirmed per order, without estimation filling.
Related pages: Immersion Chiller, Liquid Nitrogen Quick-Freezing Tunnel, Selection Q&A.