Reefer containers: how they work and what they cost

A reefer is a shipping container with an integral refrigeration unit. It is not an insulated box that keeps cold in — it is a working machine that makes cold, and it needs power for the entire journey: plugged into the terminal at the port, into the vessel’s reefer sockets at sea, and into a genset on the road.

The common sizes are 20ft and 40ft, with the 40ft high-cube being the standard for most fresh produce. Usable internal volume is smaller than a dry container of the same nominal size, because the machinery takes up one end.

What it controls #

Temperature, obviously, held to a setpoint through the voyage. Ventilation — fresh air exchange, measured in cubic metres per hour, which lets respiring produce vent CO₂ and ethylene. Humidity, on units that support it.

Some cargo also travels under controlled atmosphere, where oxygen and CO₂ levels are actively managed to slow ripening. That is a specification you order and pay for, not something every reefer does.

The setpoint is a commercial decision made before loading. Getting it wrong is not recoverable at destination.

The temperature log #

Every reefer records its actual temperature through the voyage, at intervals, and that log can be downloaded at the end. This is the single most valuable document in a quality dispute.

Fruit that arrives soft has either a pre-shipment problem or a cold-chain problem, and the log is the only thing that distinguishes them. Pull it as a matter of routine rather than only when there is an argument — by the time there is an argument, the container has usually been returned and the data is harder to get.

The container number is not your shipment #

A container number — MSKU1234567, four letters then seven digits under ISO 6346 — identifies the physical box, not your cargo and not your voyage.

That box is an asset the line reuses. It was carrying somebody else’s fruit last month and it will carry somebody else’s next month, for fifteen or twenty years, until it is scrapped. The same number will appear on dozens of unrelated shipments in its lifetime.

This has consequences importers run into constantly:

• A container number is not a unique reference for a shipment. Two of your own shipments a year apart can legitimately carry the same number.
• Tracking a bare container number can return the wrong voyage. It answers “where is this box”, which is only your question while your goods are in it.
• Tracking stops being about you once the empty is returned. After that the number keeps producing perfectly good data about somebody else’s cargo.
• Historic tracking data on a number is not your shipment history.

The bill of lading number is the reference that identifies your consignment with the carrier, which is why it is the better long-term key — one B/L often covers several containers, and it stops meaning anything once the contract is complete rather than carrying on into someone else’s voyage.

Trackberry ties a tracking registration to the shipment rather than to the box, so a container that comes back around later starts a new registration instead of appending to an old one.

Why reefers cost more to be late with #

Two things compound:

• Free time is shorter. Typically 2–4 days at destination against 5–7 for dry.
• The daily rate is higher. Reefer detention and demurrage tariffs are materially above dry equivalents, because the equipment is scarcer and more expensive.

A delay that is an annoyance for dry cargo is a real cost here — and it is running on a shorter clock. See free time for how the two interact.

FAQ #

What temperature should my container be set to? #

It depends on the produce, and it is set before loading — avocados, grapes and asparagus all want different setpoints, and some want controlled atmosphere as well. Get it from your exporter or your own protocol; it is not something to adjust in transit.

Can I get the temperature log after the container is returned? #

Sometimes, from the line, but it gets harder and slower. Download it on arrival as routine — the cost of pulling a log you never need is nothing compared to needing one you cannot get.

Why is reefer free time shorter than dry? #

Because the equipment is scarcer, more expensive and in constant demand. Lines price the box’s time accordingly, which is why the cargo with the least tolerance for delay runs on the shortest clock.

Is a container number unique to my shipment? #

No. It identifies the box, which the line reuses for fifteen or twenty years across dozens of unrelated shipments. Two of your own consignments a year apart can carry the same number. The bill of lading number is what identifies your consignment.

Does a reefer keep working if it loses power? #

No. It is a machine, not a cool box. It holds temperature for a while through insulation and thermal mass, but an extended unplugged period — waiting for a plug at a busy terminal, for instance — is a genuine cold-chain risk.