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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.
What the equipment does
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 where the air reaches 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 does not see.
Chilled and frozen behave differently
| Mode | 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. Chilled loads therefore need a fresh air exchange setting, and a produce load shipped with the vent closed arrives spoiled with a perfect temperature record.
Pre-trip inspection
Before a reefer is released for loading, a pre-trip inspection confirms the unit runs, holds temperature and records data. Ask for it. A failed unit found at the stuffing point is an inconvenience; one found on arrival is a total loss claim that your insurer contests by asking whether you verified the equipment.
Stuffing discipline
- Pre-cool the cargo before loading. The container maintains, it does not chill.
- Pre-cool the container where the carrier's procedure calls for it, and load quickly to avoid condensation.
- Do not block the floor channels or the evaporator.
- Stay below the load line.
- Use pallets that allow airflow, and avoid solid pallet bases where the stow pattern needs bottom air.
- Record the pulp temperature at loading, not just the ambient.
The FDA sanitary transportation rule for food loads
Every refrigerated food load that moves in the United States falls under 21 CFR 1.908, which assigns temperature responsibilities to four parties:
| Party | Duty under 21 CFR 1.908 |
|---|---|
| Shipper | Specifies the operating temperature to the carrier in writing, including the pre-cooling phase, and keeps written procedures for adequate temperature control |
| Loader | Verifies before loading that each mechanically refrigerated container is adequately prepared, including pre-cooling where needed |
| Carrier | Meets the shipper's specifications, pre-cools the unit as specified and, on request, shows the temperature was maintained |
| Receiver | On receipt, assesses whether the food suffered significant temperature abuse by checking the food temperature, the ambient temperature, the temperature setting and a sensory inspection |
Temperature records carry legal weight under this rule. Shippers keep the specification and procedure records for 12 months beyond the end of the carrier agreement (21 CFR 1.912), and every party makes the records available promptly on request. If any party sees an indication of a possible material failure of temperature control, the food is not sold or distributed until a qualified individual determines the deviation did not make it unsafe (21 CFR 1.908(a)(6)).
In-transit cold treatment for fruit
Some fruit enters the United States only after a cold treatment that kills quarantine pests, and a reefer container can serve as the treatment enclosure. 7 CFR 305.6 sets the conditions, and they are stricter than commercial practice:
- Pre-cooling: the fruit must be pre-cooled to no more than the highest temperature of the treatment schedule before treatment starts. An APHIS official takes pulp temperatures from a sample, and a pallet 0.28 °C (0.5 °F) or more above that temperature is rejected and returned for more pre-cooling.
- Stability: pulp temperatures cannot vary by more than 0.39 °C (0.7 °F) between two consecutive hourly readings, or the treatment is invalid unless an APHIS official verifies the temperature stayed at or below the treatment temperature.
- Probes: a minimum of three temperature sensors for containers and four for vessel holds.
- Stowage: double-stacking of pallets is not allowed, and only one type of fruit in one type of package goes in a container.
- Seal: a numbered seal goes on the doors of the loaded container and is removed only at the port of destination by an APHIS official.
- Records: recording devices must log date, time, sensor number and continuous temperature, and generate charts for the inspector. If records are manipulated, the container can be suspended from cold treatments until recertified.
The treatment clock starts when all probes reach the schedule temperature. A load that is loaded warm starts the clock late.
Equipment and training duties
The sanitary transportation rule also covers the equipment. Under 21 CFR 1.906, transportation equipment for food that needs temperature control must be designed, maintained and equipped to provide adequate temperature control, and must be kept in a sanitary condition that prevents contamination. Under 21 CFR 1.910, a carrier that takes responsibility for sanitary conditions in a written contract trains its personnel on food safety problems, sanitary transportation practices and the carrier's responsibilities, on hiring and after that as needed, and keeps training records. Ask the carrier for the written procedures and the training records in the booking stage, because the carrier retains them for 12 months under 21 CFR 1.912.
A booking checklist for a reefer load
- Written operating temperature, with the pre-cooling phase, sent to the carrier by the shipper.
- Vent setting: open for chilled produce, closed for frozen.
- Pre-trip inspection record for the unit.
- Pulp temperature at loading, recorded and signed by the loader.
- Prior notice confirmation number for FDA, filed 8 hours or more before vessel arrival.
- Certificates timed against the sailing date.
- Plan for plug-in at the terminal, and a named person to collect the container on the day it is available.
Documentation
Perishable cargo, and food and beverage cargo in particular, carries more paperwork than dry freight. Expect phytosanitary or veterinary certificates, health certificates, origin documentation and import permits for the commodity and the destination, alongside the commercial invoice and packing list. Many of these have validity windows measured in days, so time them against the sailing and do not obtain them in advance and forget them.
For food entering the United States, FDA prior notice must be submitted and confirmed no less than 8 hours before the vessel arrives at the port of arrival, 4 hours for air, 4 hours for rail and 2 hours for road (21 CFR 1.279). Through the ABI/ACE system the notice cannot be submitted more than 30 calendar days before the anticipated arrival. The facility that holds the food after entry must also be registered with FDA under 21 CFR 1.225, which applies to any facility that manufactures, processes, packs or holds food for consumption in the United States unless an exemption applies.
Temperature data logs must be kept. If the cargo is claimed, the download from the unit is the evidence, and the carrier must demonstrate on request that the temperature was maintained, for example with time and temperature data taken during the shipment (21 CFR 1.908(e)(2)). Insurance mechanics are in cargo insurance for ocean freight.
Cost realities
Reefer freight is priced above dry freight, and it carries plug-in charges at terminals and monitoring costs. Reefer plug capacity on a vessel is finite, so a reefer booking can be rolled when plugs run out. A plugged container occupies a scarce slot at the terminal, so plan collection tightly, using demurrage and detention as the checklist.
Where the cold chain continues on land
The container is one link. Cargo that arrives frozen or chilled moves to a temperature-controlled warehouse or to a cross-dock, and the rule above applies to that move too. Interworld Freight is FDA registered, and the Miami operation offers FDA warehousing and cold storage for the land leg. The cold chain solutions page, the guide to shipping frozen and refrigerated items and the multi-temperature logistics service cover the different temperature bands in one movement.
FAQ
Does a reefer container cool the cargo down?
No. It maintains the temperature of cargo that is already at the required temperature. Load pre-cooled product.
What is the fresh air vent for?
Chilled produce respires. The vent exchanges air to remove carbon dioxide and ethylene. Frozen loads run with it closed.
What is a pre-trip inspection?
A check confirming the refrigeration unit runs correctly and records data before the container is released for loading.
Are temperature records available after the voyage?
Yes, the unit logs data and the carrier supplies the download. Under 21 CFR 1.908(e)(2) the carrier demonstrates on request that it kept the operating temperature the shipper specified. Request the download immediately if a problem is suspected.
Can reefers be shipped as LCL?
Consolidated temperature controlled services exist on some lanes, and they are far less common than dry LCL, because the commodities in one box must share the same temperature and air management.
Who sets the temperature for a refrigerated food shipment?
The shipper. Under 21 CFR 1.908(b)(2) the shipper specifies the operating temperature to the carrier in writing, including the pre-cooling phase where needed.
When must FDA prior notice be filed for ocean freight?
No less than 8 hours before arrival at the port, and not more than 30 calendar days before the anticipated arrival when it is filed through ABI/ACE (21 CFR 1.279).
Can a reefer container be used for quarantine cold treatment of fruit?
Yes, under 7 CFR 305.6, when it meets the treatment schedule: pre-cooled fruit, a maximum 0.39 °C variation between consecutive hourly pulp readings, at least three temperature sensors, no double-stacked pallets, one fruit type per container and a numbered seal removed only by an APHIS official at the destination port.
What records must a food carrier keep?
The written procedures for sanitary conditions, temperature compliance and bulk vehicles, and the training records of its personnel, each for 12 months under 21 CFR 1.912.
Moving perishables into the Caribbean or Latin America? Talk to us about equipment, pre-cooling and the document calendar.
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