Cold storage for eel preserves all nutrients and safety

This article sets out the standard storage temperatures for each intended use, compares the cold store types suitable for commercial eel, the HACCP-compliant operating procedure, reference installation costs by scale, and the common technical errors to avoid.

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The correct storage temperature for eel in a cold store

The temperature inside an cold storage eel is what determines the commercial value and freshness of the product. Setting the wrong threshold is the common cause of the flesh structure changing, freezer burn or weight loss through dehydration. Depending on the state of the finished product, Tân Long's engineers recommend the following specifications:

Storing whole fresh eel (0°C to 2°C)

For live or unprepared eel, an cold storage eel needs to hold a temperature band of 0°C to 2°C with a relative humidity of 90% to 95%. At this temperature, enzyme activity and micro-organisms are slowed to a minimum while the flesh is not frozen, preserving the characteristic flavour and natural firmness.

• Storage time: Three to five days for unpackaged product and up to seven days with vacuum packing.
• Technical notes: The temperature must not be allowed below -0.5°C, because localised freezing ruptures the cell tissue, leaving the eel mushy and watery after cooking. To control this precisely, the system normally uses a control cabinet with sensitive temperature sensors.

Storing frozen eel for export (-18°C to -22°C)

This is the standard temperature for prepared eel, eel fillet or packed eel for export markets such as Japan and the EU. In long-term cold storage eel , the temperature has to stay steady between -18°C and -22°C to stop enzyme and microbial activity completely, allowing storage for six to 12 months.

For the best quality, eel has to go through two demanding cooling stages:

• Quick freezing stage: Before entering storage, eel must be processed in a IQF conveyor or contact freezer at an extreme -35°C to -40°C. This technology forms ultra-fine ice crystals, protecting the integrity of the cell tissue.
• Storage stage: After freezing, the eel moves to the storage freezer. Here the Mycom refrigeration compressor or Bitzer system supplied by Tân Long holds the temperature steady, minimising movement when goods are moved in and out.

Investing in the system cold storage eel built to standard not only helps a business meet demanding certifications such as HACCP or the Codex standard but optimises profit by reducing the rate of defective and spoiled product in international distribution.

Cold store types suitable for commercial eel

System selection cold storage eel that is optimal depends on three core factors: the state of the product (live or frozen), the storage scale and the standard of the target market. Below is a summary of the cold store solutions Tân Long's specialists most commonly design and build:

Cold storage type	Operating temperature	Eel storage time	Suited to
Dedicated chill room	0°C to 4°C	3 to 7 days	Fresh eel awaiting sale, buying stations
Freezer store	-18°C to -22°C	6 to 12 months	Prepared eel, commercially packed fillet
Combined cold store	0°C to -22°C	By temperature zone	Multi-purpose processing facilities
Quick freezing system	-35°C to -40°C	Freezing stage	Export eel fillet, industrial processing

Chill room for live fresh eel awaiting sale

A chill room running at 0°C to 4°C is the ideal choice for farms, buying stations and domestic distributors needing to keep the product fresh short term. To achieve optimum insulation in Vietnam's climate, Tân Long uses a standard 100mm insulated panel envelope.

This structure is combined with a industrial refrigeration sized accurately to the store's heat load, so the cold air is distributed evenly and localised hot spots that spoil product are eliminated entirely.

Freezer store for prepared and export eel

For long-term storage at seafood plants or exporters, a frozen cold storage eel must hold a steady band of -18°C to -22°C.

• Insulation construction: The envelope uses 150mm panel to achieve an extremely low heat transfer coefficient (U-value below 0.23 W/m²K), fully meeting the TCVN 5844 standard for seafood cold stores.
• Refrigeration and electrical system: The key element in this type of store is a refrigeration compressor screw or high-capacity piston compressor. Combined with a evaporative condenser, the system runs reliably 24/7, holding the deep temperature regardless of how often goods move in and out.

Tân Long has designed and built cold storage eel systems directly for a long list of major partners from Cà Mau to Nghệ An, making sure the finished eel retains its full nutritional value and meets the most demanding standards of the Japanese and EU markets.

The post-harvest eel storage process in a dedicated cold store

A compliant eel storage process has to start at the moment of harvest at the pond. Any break in the cold chain causes irrecoverable damage to the quality of the flesh, significantly reducing the commercial value by the time it reaches the cold storage eel.

Preparing and handling eel before it enters the store

After harvest, eel needs to be held in clean tanks with continuous aeration. Keeping the water at 10°C to 15°C for four to six hours lets the eel purge its gut and reduces physiological stress. This stage is critical to removing waste matter, which minimises the risk of cross-contamination when the eel enters the cold storage eel.

After grading by size and removing weak individuals, preparation is carried out as follows:

• For fresh eel: Cleaned and moved straight into the chill room to stay fresh.
• For frozen eel: After filleting to HACCP standard, the eel is washed in cold water at 2°C to 4°C and vacuum packed. Before entering the storage freezer, the product must go through deep freezing in a air blast freezer or system IQF freezer conveyor to lock in cell quality.

Temperature control and operational management of an eel cold store

To keep eel in perfect condition, the control system has to operate extremely accurately:

1. Automatic logging system: The temperature inside an cold storage eel must be updated at least every 30 minutes. Tân Long integrates a PLC and SCADA control panel so the owner can monitor the data in real time, meeting the demanding traceability standards of international markets.
2. Managing heat loss: The time the cold storage door is open should be limited to under three minutes per movement. Using a high-quality insulated door from Tân Long prevents heat and humidity entering from outside, protecting the stability of the product.
3. How goods are stacked: Finished eel must be placed on plastic pallets or stainless steel racking, at least 10cm off the floor and 15cm from the wall. This spacing ensures the cold air from the evaporator circulates throughout, so every position in the store reaches the standard temperature.
4. Regular cleaning: The store should be disinfected every two weeks with a suitable chlorine solution and dried completely before goods go back in. This prevents mould and bacteria developing in the cold, damp environment.

Operation cold storage eel done to the correct procedure not only keeps eel fillet at its best quality but optimises the monthly running cost.

The cost of installing an eel cold store

The cost of installing an eel cold store depends on the storage scale (in tonnes), the type of store (chilled or frozen), the panel material, the compressor technology and how automated the control system is. The table below gives reference costs for 2025 in the Vietnamese market.

Note: the costs above exclude the three-phase electrical infrastructure, the store foundation and ancillary works. Tân Long provides a free on-site survey and quotation.

The three biggest factors in the total cost are the compressor technology (a piston compressor costs 20 to 30% less than a screw compressor but has a shorter life and lower energy efficiency), the insulation panel thickness (100mm for a chill room, 150mm for a freezer store), and the level of control panel automation (basic PLC or SCADA remote monitoring).

Running energy cost is a long-term factor to include in the total cost of ownership. A 10-tonne freezer store consumes about 80kWh to 120kWh a day depending on ambient conditions and how often goods move, equivalent to VND 2.4 million to 3.6 million a month at current industrial electricity prices. An evaporative condenser in place of an air-cooled condenser can reduce energy consumption by 15 to 25% in the hot, humid climate of southern Vietnam.

Common errors when storing eel in a cold store

Most of the quality loss in eel in a cold store comes not from poor equipment but from operating errors. The five errors below account for more than 80% of the incidents recorded in practice at seafood storage facilities.

• Setting a temperature that does not match the state of the product: Many facilities use the same freezer store (-18°C) for fresh eel awaiting sale. At that temperature the fresh eel freezes uncontrolled, loses its flesh structure and cannot be sold fresh after thawing. Fresh eel for short-term storage needs a separate chill room at 0°C to 2°C.
• Heavy frost on the evaporator from not defrosting on schedule: When frost on the evaporator is thicker than 5mm (0.2 inch), heat exchange efficiency falls sharply and the store does not reach its set point even with the compressor running continuously. The automatic defrost should be set two or three times a day, 20 to 30 minutes each time, depending on the moisture load of the goods in the store.
• Storing eel together with strong-smelling seafood: Eel absorbs the odour of squid, tuna and shrimp without a partition or isolating packaging. A store holding several species needs clear zoning or completely sealed packaging for the eel.
• Not controlling the store humidity: A freezer store that is too dry (below 80% RH) causes freezer burn on the surface of the eel after two to three months' storage. This creates dry, silvery-white patches on the skin which cannot be reversed and significantly reduce commercial value, even though the product is still safe to eat.
• Not logging the temperature and not applying FIFO: No temperature control record means not qualifying to export to markets that require HACCP. Not applying FIFO (first in, first out) means eel that arrived later goes out first, leaving older eel in store beyond its shelf life.

The benefits of cold storage in the commercial eel supply chain

An eel cold store creates value at three points in the supply chain: at the farm, at the processing facility and at the distribution point.

• At an eel farm, a cold store allows harvesting in large batches rather than piecemeal to daily market demand. That optimises the harvest schedule, reduces labour cost and gives more room to negotiate price with buyers. An intensive eel farm of one hectare or more normally harvests 500kg to 2 tonnes per crop. Without a cold store, all of it has to be sold within 24 hours or accept a low price from the traders.
• At a processing facility, a freezer store extends production year round, free of the eel harvest season (normally April to October in the Mekong Delta provinces). Eel bought when prices are low is frozen and stored, then processed and exported when the market is better.
• At the distribution and export point, an unbroken cold chain from store to refrigerated vehicle to port is mandatory to meet the food inspection requirements of Japan (JAS/HACCP), the EU (Regulation EC 853/2004) and many Southeast Asian markets.

Tân Long, a trusted eel cold store designer and installer in Vietnam

Tân Long Refrigeration Electro-Mechanical Joint Stock Company has more than 20 years of deep experience in consulting on, designing and building industrial refrigeration systems, particularly cold storage eel and seafood stores in Vietnam. Founded in 2005 and with its own modern equipment factory in Tây Ninh since 2008, Tân Long is now established among the five largest refrigeration and electro-mechanical companies in the country. With HACCP certification, we guarantee outstanding technical capability for cold store projects meeting demanding international export standards.

Technical capability and notable seafood projects

Tân Long has established its position by delivering large-scale refrigeration systems, a solid foundation for high-quality commercial cold storage eel solutions:

• Frescol Tuna Vietnam project (Nghệ An): Design and construction of a 12,000-tonne cold store using a complete NH3 refrigeration system.
• Strategic partners: Systems delivered for industry leaders such as Ca Mau Seafood Processing and Service Joint Stock Company (CASES) and Vietnam Clean Seafood Joint Stock Company (Sóc Trăng).
• Operating standard: Every system has strict temperature control, preserving maximum freshness and nutritional value in high-value seafood.

The professional eel cold store consulting and installation process

At Tân Long, every cold storage eel project is personalised through an on-site survey and free design consultation at the site:

1. Survey and design: Analysing the specific storage requirement and the site conditions to produce the technical design file, with an accurate heat load calculation.
2. Construction and installation: Installing the insulated panel envelope directly, integrating a high-capacity refrigeration compressor unit and a smart control panel.
3. Acceptance and handover: Test running, detailed operator training and setting up the scheduled maintenance regime.

Tân Long's technical team is on duty 24/7 to deal with anything that arises, so the customer's cold chain is never interrupted. The biggest difference is that Tân Long manufactures core equipment such as IQF conveyor, contact freezer and wind tunnel at its own factory, which optimises the investment cost and shortens the lead time for replacement equipment.

Tan Long contact information:

• Address: 86 Dong Den, Ward 14, Tan Binh District, Ho Chi Minh City
• Phone: (+84) 933 357 058 (Mr. Thịnh)
• Email: info@tanlongvn.com
• Website: tanlongvn.com

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