Freezing is the process of bringing the temperature of food below freezing (-18°C or lower) in the shortest time possible, so as to shut down the micro-organisms and the spoilage enzymes completely. When the cooling rate is fast enough, the ice crystals that form are small, under 50 micrometres, and do not rupture the cell membranes, so the tissue structure, the flavour and the nutritional value survive thawing intact.
In food processing, freezing is not merely storage: it is the technical stage that determines the output quality of the entire production chain. In this article Tân Long sets out the full grounding in industrial freezing: the thermodynamics, the classification of methods, the operating parameters, and how to choose the right equipment for each product line.
What does freezing mean in the food industry?
In modern refrigeration engineering, the term What is freezing? is defined as quick freezing, bringing the product core down to the standard -18°C (0°F). Under the strict requirements of Codex Alimentarius (the FAO/WHO international food standard) and TCVN 5602:2008 in Vietnam, that has to be completed within 30 minutes to 4 hours. To achieve it, businesses generally use a air blast freezer system or a purpose-built air blast freezing tunnel installation.
The key thing separating freezing from ordinary chilling is the speed at which the product crosses the zone of maximum crystal formation (-1°C to -5°C). Passing through that danger zone very fast, the intracellular water changes phase into tiny ice crystals, evenly dispersed. Take longer than 30 minutes, by contrast, and the large ice crystals that form puncture the cell membranes, causing water loss on thawing and leaving the product mushy and weeping, with a weight loss of 3% to 8%. That is why IQF conveyor technology has become the best answer for protecting food structure.
Microbiologically, anything below -12°C suppresses most pathogenic and spoilage bacteria. At -18°C, water activity (aw) falls below 0.85, the point at which micro-organisms all but stop growing. Endogenous enzymes such as lipase and protease still work slowly at that temperature, however. So on projects installing cold storage for export seafood, the engineering team at Tan Long always recommends holding storage at -25°C (-13°F), to give a shelf life of up to 24 months with the fresh flavour fully intact.
How industrial freezing equipment works
Industrial freezing equipment works on the vapour-compression refrigeration cycle, in which the refrigerant absorbs heat from the product and rejects it through the condenser. Freezing performance depends on three core technical factors: the heat transfer coefficient, the circulating air velocity, and the contact area between the refrigerant and the product.
- Heat transfer and the coefficient of performance: Freezing rate is governed by Fourier's law of conduction and Newton's law of convection. In air blast freezing, the convective heat transfer coefficient reaches 20 to 50 W/m²K at an air velocity of 3 to 5 m/s. Raise the velocity to 10 m/s and that rises to 80 to 120 W/m²K, cutting freezing time by 30% to 50%. Too high a velocity, though, increases fan power consumption and causes surface moisture loss (freezer burn) if the product is unwrapped.
- Refrigerant in the freezing system: Most industrial freezing equipment in Vietnam today uses one of two refrigerants. Ammonia (R717) has a coefficient of performance (COP) of 3.5 to 4.5 at an evaporating temperature of -35°C, but it is toxic above 25 ppm, so it requires leak detection and a well-ventilated plant room. HFCs (R404A, R507) are safer but carry a high GWP (global warming potential) and are being phased down under the Kigali Amendment, which Vietnam signed in 2019.
- Temperature and humidity control: PLC control panel in modern freezing systems reads the temperature from a Pt100 sensor (accurate to ±0.1°C) and adjusts the electronic expansion valve (EEV) by the second, holding the chamber temperature within ±0.5°C. Relative humidity in the freezing chamber is held at 90% to 95% to limit surface moisture loss, through scheduled defrost cycles and control of the air flow.
Classifying industrial freezing methods
Industrial freezing methods are classified by the mechanism of heat transfer between refrigerant and product. Each has its own operating temperature range, freezing rate, and suitability for particular products. The table below summarises the four most common methods in Vietnamese food processing.
| Method | Heat transfer mechanism | Room temperature | Time to reach -18°C at the product core | Suited to |
|---|---|---|---|---|
| Air blast freezing | Forced convection | -35°C to -40°C | 30 minutes to 4 hours | Shrimp, fish fillet, meat blocks, prepared foods |
| Contact freezing | Direct conduction | -35°C to -45°C | 15 minutes to 2 hours | Flat fish fillet, whole shrimp in blocks, tray-packed products |
| IQF freezing (individual quick freezing) | Convection + fluidised bed | -35°C to -45°C | 5 to 30 minutes | Loose shrimp, loose squid, vegetables, fruit, rice, dumplings |
| Cryogenic freezing | Instant evaporation | -80°C to -196°C | 1 to 10 minutes | Premium seafood, products that must hold their shape, pharmaceuticals |
Air blast freezing
Air blast freezing uses forced circulation of cold air to draw heat out of the product. Air Blast Tunnel Freezers and air blast freezer works on this principle, with the chamber held at -35°C to -40°C (-31°F to -40°F) and air velocity between 3 and 8 m/s. It is the most flexible method, because it can freeze a wide range of product shapes, from whole shrimp to a 20 kg carton of meat.
The drawback of air blast freezing is a lower heat transfer coefficient than contact or cryogenic freezing, so the freezing time is longer. With a 100mm-thick block of beef, reaching -18°C at the core can take up to 6 hours even at a chamber temperature of -40°C. Weight loss from surface evaporation is typically 0.5% to 2% if the product is unwrapped.
Contact freezing
Contact freezing transfers heat through a metal surface pressed directly against the product. Contact freezer (plate freezer) uses hollow aluminium plates with refrigerant circulating inside, pressed onto both faces of the product at 0.3 to 0.5 bar. The heat transfer coefficient reaches 200 to 400 W/m²K, five to ten times that of air blast freezing, which shortens the freezing time considerably.
The method is particularly effective with 2 kg (4.4 lb) shrimp blocks and 30mm fish fillets, reaching -18°C at the core in only 45 to 90 minutes. It is not suited to irregularly shaped or loose product, however, because it needs a flat, even contact surface.
IQF freezing (individual quick freezing)
IQF freezing is the technique of freezing each piece individually, so the product does not stick together during the freeze. Mesh belt IQF freezer stainless steel belts carry the product through a zone of very high-velocity cold air (-40°C to -45°C), while vibration or a fluidised bed separates small items such as shrimp, vegetables and fruit.
Ưu điểm căn bản của IQF là người mua có thể lấy đúng lượng cần dùng mà không phải rã đông toàn bộ. Trong xuất khẩu thủy sản, IQF được yêu cầu bắt buộc với tôm rời và mực ống xuất sang Nhật Bản, EU và Mỹ. Công suất băng chuyền IQF công nghiệp dao động khoảng 300–3.000 kg/giờ với dây chuyền thông dụng, tùy kích thước buồng và tốc độ băng chuyền.
Cryogenic freezing with liquid nitrogen
Cryogenic freezing sprays liquid nitrogen (N₂) at -196°C (-321°F) directly onto the product. It freezes faster than any mechanical method, reaching -18°C at the core within 1 to 5 minutes for size 16/20 shrimp. That speed produces extremely fine ice crystals and preserves the cell structure almost perfectly, which suits premium fresh seafood such as sashimi and scallops.
Running costs for liquid nitrogen freezing are three to five times those of mechanical freezing, because it consumes roughly 0.8 to 1.5 kg of N₂ per kg of product. It is used mainly on premium export seafood lines and in medical and pharmaceutical products.
The advantages of industrial freezing over other preservation methods
To understand why every large food business favours this technology, we need to look at What is freezing? from the standpoint of economics and engineering together. Industrial freezing maintains product quality far better than ordinary chilled storage (0°C to 4°C) or traditional salting. The process shuts down both micro-organisms and natural chemical reactions without any chemicals at all. With Tân Long's solutions, a business gains five key technical advantages:
- Maximum retention of nutritional content: Detailed studies show that food processed through an IQF conveyor system retains over 95% of its protein and essential amino acids after 12 months at -18°C. That is far higher than salt-and-ice storage, which holds quality for only 7 to 10 days.
- Meeting global clean-label standards: Quick freezing removes the need for sodium benzoate, sodium nitrite or any other chemical preservative. That gives the product a clean label and easy access to demanding export markets such as the EU and Japan.
- Killing parasites and guaranteeing safety: Under FDA 21 CFR Part 113, temperatures below -18°C in dedicated cold storage systems kill parasites such as Anisakis in sea fish, making sashimi and raw fish dishes completely safe for the consumer.
- Optimising production and distribution planning: The technology lets a plant concentrate production in season, when raw material is cheapest, then store and distribute steadily all year. Solutions such as a modern air blast freezing tunnel give flexible operation at any plant size.
- Cutting economic losses: According to 2023 figures from the Vietnam Association of Seafood Exporters and Producers (VASEP), losses across the frozen supply chain run 20% to 30% lower than for fresh product. That translates directly into a better ROI on any installation of industrial refrigeration system.
Choosing the right freezing method is not only a storage question; it is a strategy for raising brand value and competitiveness in international markets.
Common industrial freezing equipment in Vietnam
Industrial freezing equipment in Vietnam falls into two main groups: batch freezing and continuous freezing. The choice between them depends on production capacity, product type and how automated the line is.
Air blast tunnels and blast freezers
Hầm đông gió (blast tunnel) và tủ đông gió (blast freezer) thuộc nhóm cấp đông theo mẻ. Nhiệt độ vận hành từ -35°C đến -40°C, công suất thiết kế theo sản lượng từng nhà máy — tại dự án NECS, Tân Long triển khai hệ thống lạnh cho hầm đông 12.200 kg/mẻ. Đây là lựa chọn phổ biến nhất với các nhà máy chế biến thủy sản và thịt tại Việt Nam do chi phí đầu tư thấp hơn so với IQF và linh hoạt với nhiều loại sản phẩm.
The blast freezer suits small to medium production, 500 kg to 2,000 kg a day. The blast tunnel suits large plants needing to freeze up to 20 tonnes a day in one go.
Contact freezer
The plate or contact freezer has 5 to 30 aluminium plates stacked one above another, each plate an evaporator. Product is loaded into tray frames between the plates, and a hydraulic system presses the plates together. A 2 kg shrimp block freezes in 45 to 75 minutes, using 15% to 20% less energy than air blast freezing of the same capacity.
This equipment suits plants processing shrimp and fish blocks for export, particularly lines that need blocks uniform in size and weight for automatic packing.
IQF conveyor
The IQF tunnel freezer is continuous equipment, suited to a line running 16 to 24 hours a day. Capacity ranges from 500 kg/hour to 3,000 kg/hour (1,100 lb/hour to 6,600 lb/hour) depending on the model. A mesh-belt IQF conveyor suits shrimp, squid and cut vegetables; a flat-belt IQF conveyor suits thin fish fillets and formed products.
Investment in a 1,000 kg/hour IQF conveyor line runs from VND 2 billion to VND 5 billion (roughly USD 80,000 to USD 200,000), higher than a blast freezer, but labour cost per unit of product is appreciably lower thanks to the automation.
The technical parameters that matter when choosing freezing equipment
Choosing the right freezing equipment means analysing three groups of parameters carefully: thermal capacity, operating conditions and product requirements. The most common mistake in practice is sizing the equipment on nominal throughput while ignoring heat loss from the surroundings, the heat load of the packaging, and how often the door is opened to load.
| Parameter | Unit | Reference level | What it affects |
|---|---|---|---|
| Freezer temperature | °C / °F | −35°C to −45°C (−31°F to −49°F) | Freezing rate and ice crystal quality |
| Air velocity (air blast freezing) | m/s | 3 to 8 m/s | Heat transfer coefficient, surface moisture loss |
| Time to reach -18°C at the core | minutes / hours | Depends on the product | Throughput and product quality |
| System COP | dimensionless | 2.5 to 4.5 | Running cost for electricity |
| Freezing capacity (kW or TR) | kW / Ton Refrigeration | Calculated from the actual heat load | Equipment size and capital cost |
| Refrigerant | type | R717 or R507 | Safety, cost, plant room requirements |
To size the equipment, you have to establish three components of the heat load: the heat to be removed from the product (Q₁), the heat load from the chamber structure and the surroundings (Q₂), and the operating heat load from fans, lighting and defrost (Q₃). Actual equipment capacity is normally set at 1.15 to 1.25 times the total (Q₁ + Q₂ + Q₃), to leave an operating margin.
The correct freezing procedure in a food plant
To meet the industrial storage standard properly, understanding the nature of What is freezing? is not enough on its own: a business has to follow a strict operating procedure of seven consecutive steps. Every stage in that cycle bears directly on the structural quality of the food and on the electricity consumption of the whole system. Any technical slip can lengthen the freezing time, waste energy and reduce the value of the product. The engineering team at Tan Long always recommends the following standard procedure:
- Step 1: Intake and temperature conditioning of the raw material: Before it goes into the equipment, the raw material has to be brought down to between 0°C and 4°C. That avoids a sudden heat load, protects the refrigeration compressor from overloading, and prevents a rise in chamber temperature that would affect the batches already being processed.
- Step 2: Grading and uniform preparation: The product has to be graded to a uniform size so that the core reaches -18°C at the same moment throughout. If sizes vary by more than 30%, the small pieces will be over-frozen while the large blocks have yet to reach temperature at the centre.
- Step 3: Loading the product into the equipment: How the product is arranged depends on the equipment. In a blast freezer, it has to be laid out in a single layer on trays with at least 10mm between pieces, so the cold air circulates evenly. In a contact freezer, by contrast, it has to be packed tightly into the tray frames to maximise the contact area with the plates.
- Step 4: Running the system to its design parameters: One important rule: never load more than 80% of the equipment's design capacity in a single batch. Overloading pushes the chamber temperature up by 5°C to 8°C and lengthens the freezing time by 20% to 40% over the expected figure.
- Step 5: Checking the core temperature of the food: Before the cycle ends, the technician has to push a probe thermometer into the centre of the thickest piece. Only once the reading confirms the core has reached -18°C should the batch leave the freezing chamber.
- Step 6: Transfer to the cold store: Once the freeze is complete, the product has to be moved into cold storage within three minutes. Moving it quickly prevents surface thawing, which is the main cause of pieces sticking together in loose-frozen product lines.
- Step 7: Cleaning and scheduled defrost: A 5mm layer of frost on the industrial refrigeration can cut system performance by 15% to 25%. Defrosting every 8 to 12 operating hours is therefore mandatory, to maintain the optimum heat exchange coefficient.
Following this procedure properly does more than establish a business's reputation for product quality: it is a sustainable way to cut running costs over the long term.
Quality standards that apply to industrial freezing
Setting the technical standards that answer the question of What is freezing? is decisive for a food business's ability to export and for its reputation. Processors in Vietnam today have to apply national (TCVN) and international standards together to govern deep freezing rigorously. These standards not only ensure hygiene and safety but also optimise the performance of modern industrial refrigeration systems . Specifically, a plant has to comply with the following:
- TCVN 5603:2008 (equivalent to Codex CAC/RCP 1-1969): This is the foundation standard, setting a minimum of -18°C for frozen product and requiring clear labelling of production date and expiry date on the packaging.
- TCVN 9616:2013: This standard covers storage temperature and the transport procedure for frozen seafood throughout the cold chain.
- Regulation (EC) No 853/2004: For goods exported to the EU, the plant has to meet the hygiene regulation for food of animal origin, under which the core temperature of product leaving the cold store must never exceed -18°C (0°F).
Beyond the regulatory standards, the HACCP food safety management system (Hazard Analysis Critical Control Points) is central to quality control at the plant. Within it, technicians have to identify and monitor two critical control points. The first is CCP1, making sure the product core reaches -18°C the moment the freezing cycle ends. The second is CCP2, holding storage temperature steady below -18°C for the whole time the product is in store.
To control those critical points precisely, the specialists at Tan Long generally advise integrating an intelligent PLC control panel system. It records data continuously and raises an immediate alarm on any temperature deviation, so management can take corrective action promptly under the approved HACCP plan, protecting the value of the product all the way to the consumer.
Complete industrial freezing solutions from Tân Long
Tân Long is proud to be a pioneer in advising on, designing and installing industrial refrigeration systems in Vietnam, with more than 20 years behind it. To answer the question of What is freezing? properly, and of how to apply it effectively, we supply a full range of equipment, from small-scale production through to modern export processing plants. Tân Long's freezing solutions are engineered for very fast freezing and outstanding energy efficiency, and include:
- Mesh-belt IQF conveyor and Flat IQF conveyor: The first choice for loose products such as shrimp, squid, fruit and vegetables, holding the shape and the quality of each individual piece.
- Air blast freezing tunnel: Purpose-designed for blocks, carcass meat or large cartoned products that need strong convective cold air flow.
- Blast freezer: Flexible operation across a range of product trays, suiting processors handling several product lines.
- Contact freezer: The best answer for block products that need direct heat transfer through a metal surface to reach deep sub-zero in the shortest time.
Tân Long's experienced engineers are always ready to work with customers on calculating the real heat load, and to advise on the equipment that best fits each plant's particular products and output targets. Investing in a properly engineered industrial refrigeration system does more than protect the value of agricultural and seafood products: it strengthens your position in international markets. For free technical support and a detailed quotation, please contact Tân Long directly on (+84) 933357058, or visit our freezing equipment section today.
Frequently asked questions about freezing
What is the difference between freezing and chilling?
Chilling brings the product down to around 0°C to 4°C, keeping food fresh for 3 to 10 days. Freezing takes the temperature below -18°C, turning the intracellular water to ice, shutting down micro-organisms completely and extending storage to 6 to 24 months. Both use the same refrigeration principle but differ in target temperature and in the cooling rate required.
Why does quick freezing matter more than slow freezing?
Quick freezing crosses the crystallisation zone (-1°C to -5°C) in under 30 minutes, forming ice crystals smaller than 50 micrometres that do not rupture the cells. Slow freezing stretches that stage to 2 to 6 hours, and the large crystals, 200 to 500 micrometres, puncture the cell membranes, so the product loses 3% to 8% of its cell fluid on thawing.
Which freezing equipment suits a medium-sized seafood plant?
A seafood plant running 3 to 10 tonnes a day typically chooses a contact freezer for shrimp blocks and a blast tunnel for whole shrimp and loose-frozen fish fillet. If the main product is loose IQF shrimp for export, an IQF conveyor of 500 to 1,000 kg/hour is the better choice on both throughput and product quality.
Frequently asked questions about freezing
What is freezing?
Freezing is the process of bringing a product's temperature rapidly below its freezing point so that most of the water in it turns to ice, suppressing micro-organisms and extending storage life.
How does freezing differ from chilled storage?
Freezing is the rapid cooling stage, carried out over a short period with high-capacity equipment. Frozen storage is the stage that follows, simply holding the temperature already reached, in a store, over a long period.
Why does freezing have to be fast?
Because slow freezing produces large ice crystals that tear the cell structure, so the product weeps heavily and loses quality on thawing. Fast freezing produces small crystals and preserves the structure far better.
What freezing methods are there?
The common ones are air blast freezing (blast freezer, IQF conveyor), contact freezing (plate freezer) and immersion freezing in a liquid refrigerant. The choice depends on the shape and size of the product and on the quality required.
Does Tân Long supply freezing equipment?
Yes. Tân Long designs and builds freezing systems for seafood, meat and agricultural processing plants, together with matched refrigeration plant and cold stores.
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