A refrigerated container maintains a temperature. It does not lower one. That is the first thing to understand about temperature controlled shipping. That single fact explains most reefer claims: cargo loaded warm arrives warm, and no amount of set point adjustment during the voyage fixes it.
A reefer unit circulates air at a set temperature through the container. Air enters under the floor through T-bar decking, rises through the cargo and returns to the unit. The system controls the air, and the cargo follows the air only if the air can reach it.
That is why stow pattern matters as much as the set point. Cargo blocking the T-bar floor, stacked above the red load line, or packed tight against the doors interrupts circulation and creates hot spots that the return air sensor never sees.
| Mode | Typical purpose | Air management |
|---|---|---|
| Frozen | Hold product below freezing | Sealed, minimal fresh air exchange |
| Chilled | Hold fresh produce or dairy in a narrow band | Fresh air vent open to remove respiration gases |
| Controlled atmosphere | Extend life of respiring produce | Gas mix actively managed |
Fresh produce respires, generating heat, carbon dioxide and ethylene. That is why chilled loads need a fresh air exchange setting, and why a produce load shipped with the vent closed can arrive spoiled with a perfect temperature record.
Before a reefer is released for loading it should have a pre-trip inspection confirming the unit runs, holds temperature and records data. Ask for it. A failed unit discovered at the stuffing point is an inconvenience; one discovered on arrival is a total loss claim that your insurer will contest by asking whether you verified the equipment.
Perishable cargo, and food and beverage cargo in particular, carries more paperwork than dry freight. Depending on commodity and destination, expect phytosanitary or veterinary certificates, health certificates, origin documentation and import permits, alongside the commercial invoice and packing list. Many of these have validity windows measured in days, so they have to be timed against the sailing, not obtained in advance and forgotten.
Temperature data logs should be kept. If the cargo is claimed, the download from the unit is the evidence, and the party that produces it first usually controls the narrative. Insurance mechanics are in cargo insurance for ocean freight.
Reefer freight prices above dry freight, and it carries plug-in charges at terminals, monitoring costs and, on some lanes, a higher risk of rolling because reefer plug capacity on a vessel is finite. Free time is usually shorter and demurrage higher, because a plugged container occupies a scarce slot. Plan collection tightly, using demurrage and detention as the checklist.
No. It maintains the temperature of cargo that is already at the required temperature. Load pre-cooled product.
Chilled produce respires. The vent exchanges air to remove carbon dioxide and ethylene. Frozen loads normally run with it closed.
A check confirming the refrigeration unit runs correctly and records data before the container is released for loading.
Yes, the unit logs data and the carrier can supply the download. Request it immediately if there is any suspicion of a problem.
Consolidated temperature controlled services exist on some lanes but are far less common than dry LCL, and the compatibility of commodities limits what can share a box.
Moving perishables into the Caribbean or Latin America? Talk to us about equipment, pre-cooling and the document calendar.