Reefer Containers and the Cold Chain: Shipping Perishables

How to ship perishables in reefer containers: set point, ventilation, humidity, pre-cooling, airflow, PTI and data loggers, with a 40' reefer of dates.

Fresh fruit, vegetables, dates, fish, meat, dairy products, chocolate, flowers, pharmaceuticals: a large share of the world's food and medical trade depends on refrigerated transport. The reefer container made this trade possible by sea, at a fraction of the cost of air freight, but it only works if every link in the cold chain is managed.

When a perishable shipment goes wrong, the loss is often total, the claim is complex, and the cause is usually human: warm cargo loaded into a cold box, a set point typed in Fahrenheit, blocked airflow, or a container left unplugged at a terminal. Insurers and carriers will look first at what the shipper did.

This lesson explains how a reefer works, which settings you must give at booking, how to prepare and stow the cargo, how to monitor the temperature and protect yourself in case of a claim. A worked example follows a 40' reefer of Deglet Nour dates from Algiers to Surabaya.

How does a reefer container work?

A reefer is an insulated container with a refrigeration unit at one end, powered from the ship, the terminal or a generator set (genset) during road transport. The unit blows conditioned air under the cargo through a T-shaped floor (bottom-air delivery). The air rises through the cargo and returns to the unit over the top of the load.

Three consequences for you as shipper:

• The reefer maintains temperature; it does not cool cargo. Its capacity is designed to remove the heat that enters through the walls and, for fresh produce, the heat the produce generates by respiring. Warm cargo loaded into a reefer will take days to cool, if it ever does, and the cargo near the top may spoil.
• Air must circulate. The floor must be covered evenly so air rises through the cargo, not through gaps; nothing may sit above the red load line on the side walls, which leaves room for the return air.
• The power must never stop for long. Every transfer between ship, terminal and truck is a moment of risk.

Typical internal figures are about 11.58 × 2.29 × 2.55 m for a 40' high cube reefer (about 67 m³, or 65 m³ usable under the load line, payload about 29 tonnes) and 5.45 × 2.29 × 2.27 m for a 20' reefer. They vary by line; see shipping containers.

The three settings you give at booking

Set point (temperature)

The temperature the unit will maintain, written in degrees Celsius with a sign and one decimal: "+2.0 °C", "−18.0 °C". It depends on the product, its variety and maturity, and the transit time, and should come from your packer, your buyer's specification or the line's reefer department.

Chilled cargo is usually controlled on the supply air (the air leaving the unit), so no part of the load gets colder than the set point. Frozen cargo is usually controlled on the return air, which reflects the warmest part of the load.

Ventilation (fresh air exchange)

Fresh fruit and vegetables keep respiring: they consume oxygen and release carbon dioxide, water vapour and, for some, ethylene, which accelerates ripening. A vent lets fresh air in, set in cubic metres per hour (for example 15 or 25 m³/h) or as a percentage. Frozen cargo and most dry or processed goods travel with vents closed. Some produce travels in controlled atmosphere, where the unit regulates oxygen and carbon dioxide levels.

Humidity

Many units can dehumidify to a set relative humidity. Too much humidity encourages mould; too little dries the product out. Not all products need a humidity setting; ask before setting one.

Preparing and loading a reefer

1. Order a PTI-passed container (pre-trip inspection): the unit tested, the box clean, dry and odour-free.
2. Pre-cool the product in a cold store to the transport temperature, and record pulp or core temperatures.
3. Check the container's settings on the controller before loading: set point, vents, humidity, unit of measure.
4. Pre-cool the container only if you load from a sealed cold-store dock; otherwise, keep the unit off with the doors closed until loading, to avoid condensation on the walls.
5. Load quickly, with the unit off while the doors are open, then turn it on as soon as the doors close.
6. Block-stow the cargo evenly over the floor, without gaps between pallets. If part of the T-floor stays uncovered, usually at the door end, cover it with cardboard or a floor plate so the air is forced up through the cargo instead of escaping through the gap.
7. Stay under the red load line, and never stow cargo against the unit's air outlet.
8. Place independent data loggers in the load (one near the doors, one in the middle, one near the unit), record their numbers, and seal the container.

Monitoring the cold chain

Most reefers record set point, supply and return air temperatures, and alarms in their controller memory. A reefer download from the unit, which the carrier can provide on request, is the core evidence in any claim. Many lines now offer remote monitoring, with alerts if power is lost or the temperature deviates; ask for it on valuable cargo. Independent data loggers placed in the cargo add a second, shipper-controlled record.

Weak points to watch:

• the truck journey to the port (genset fitted and fuelled);
• waiting time at the terminal before plugging in;
• transshipment, where boxes are unplugged and moved;
• the delivery leg and the buyer's unloading.

Insurance and documents for perishables

Standard Institute Cargo Clauses exclude inherent vice and delay, two of the main causes of loss in perishables. Specific clauses exist for frozen and chilled food, including cover for breakdown of the refrigerating machinery under conditions set by the insurer, such as a minimum duration of breakdown. Discuss them with your broker; see cargo insurance.

Perishable food shipments also need sanitary or phytosanitary certificates, sometimes fumigation or cold treatment certificates, and must arrive with enough shelf life left for the buyer to sell. The sanitary and phytosanitary certificates lesson covers these documents.

Worked example: a 40' reefer of dates from Algiers to Surabaya

A packer in Biskra sells Deglet Nour dates to an Indonesian importer who wants them on the shelves well before Ramadan, expected to begin around 8 February 2027. Port-to-port transit with one or two transshipments in the Mediterranean and in Southeast Asia is quoted at 38 to 45 days.

Cargo: 18 pallets of 120 × 100 cm, each with 170 cartons of 5 kg (3,060 cartons, 15,300 kg net, about 16,900 kg gross), stack height 2.19 m, below the load line of the 40' high cube reefer.

Settings agreed with the packer and the line's reefer desk: set point +1.0 °C, supply air control; vents closed (the dates were fumigated, dried to shipping moisture, and do not need fresh air); dehumidification at about 65% relative humidity.

Timeline:

Cost (illustrative): reefer ocean freight and surcharges USD 5,900, origin THC and reefer plug-in USD 420, genset trucking USD 380, insurance with refrigeration-breakdown cover USD 260, phytosanitary and fumigation certificates USD 150. Total about USD 7,100, or USD 0.46 per kg of dates.

The packer keeps the pre-cooling records, the PTI certificate, loading photos and the logger data in the shipment file. If the buyer reports soft or fermented fruit, these records show what happened and where.

Common mistakes with reefer shipments

• Loading warm cargo and expecting the reefer to cool it.
• Ambiguous set points: missing sign, missing unit, Fahrenheit confusion.
• Wrong ventilation: open vents for frozen goods, closed vents for respiring produce.
• Blocking airflow with uneven stowage, solid wrap or cargo above the load line.
• Mixing products with incompatible temperatures or ethylene sensitivity.
• No independent loggers and no records, leaving nothing to support a claim.
• Not tracking the container through transshipments, where power interruptions are most likely; see tracking and transit times.