How does a reefer container work?
A reefer (refrigerated) container keeps its internal temperature at the set value with the refrigeration unit in its front wall. Cold air leaves the bottom of the unit, travels through the T-shaped channels in the floor, rises up through the cargo and returns to the unit along the roof. So the cargo itself shapes the airflow.
There are two basic types of cargo:
- Frozen: Meat, seafood, frozen food. The aim is to maintain the temperature; the cargo does not respire.
- Chilled: Fresh fruit and vegetables, flowers. The produce is still alive, respires and produces heat, so ventilation and humidity settings also matter.
Information to give at booking
- Set point: The carrying temperature. State the unit (°C or °F) clearly; mixing up units is a known cause of losses.
- Ventilation: For fresh produce, the fresh air exchange setting (m³/hour).
- Humidity: Dehumidification for some products.
- Controlled atmosphere (CA): For some fruit, shelf life is extended by adjusting oxygen and carbon dioxide levels.
These values depend on the product and are the exporter's responsibility. Follow the guidance of product specialists and the carrier.
Pre-loading checklist
Tick off the list below step by step before a reefer is loaded. Click an item to see why it matters.
Why?
Mixing up °C and °F is a known cause of losses; the set point should also appear on the bill of lading.
Why?
Fresh produce respires, so fresh air exchange is set for the product. For frozen cargo ventilation is closed.
Why?
The PTI shows that the unit and sensors have been tested; check the PTI label and date.
Why?
A reefer is designed to maintain temperature, not to cool the cargo down.
Why?
When a pre-cooled container is opened, warm humid air enters and condenses; follow the carrier's instructions.
Why?
If the line is exceeded, cold air cannot return along the roof to the unit.
Why?
The T-floor must not be covered; large gaps short-circuit the airflow.
Why?
An independent record is the strongest evidence in a claim.
Why?
Power interruptions are among the most common points where the cold chain breaks.
Why?
Missing certificates for food and plant products hold the cargo at destination and increase temperature risk.
Airflow: the most common mistake
A large share of reefer claims comes from blocked airflow:
- The cargo must not go above the red load line inside the container; otherwise cold air cannot return to the unit.
- The T-shaped floor channels must not be covered with paper, cardboard or stretch film.
- Avoid large gaps at the door end and between pallets where cold air can short-circuit.
- For fresh produce, the ventilation holes in the packaging should line up with the airflow.
Where does the cold chain break?
The cold chain means keeping a product at the right temperature without interruption from production to consumption. The riskiest points are:
- Loading warm cargo (no pre-cooling)
- Leaving the doors open for long during loading
- Power interruptions at the terminal or on the road (genset failure, container not plugged in)
- Waiting at transshipment ports
- Opening the container for a customs inspection
The container's temperature records (data logger) are the most important evidence in a claim. If needed, add a separate independent temperature recorder to the cargo.
Test yourself
- Apples at 25 °C were loaded into a reefer with the set point at 1 °C. What is wrong? (Answer: A reefer is designed to maintain temperature, not to cool cargo; the apples were not pre-cooled.)
- Why does the red load line matter? (Answer: If the cargo goes above it, cold air cannot return along the roof to the unit and the airflow is disrupted.)
- Which setting differs between frozen meat and fresh bananas? (Answer: Fresh produce needs ventilation (fresh air exchange) and often a humidity setting; for frozen cargo ventilation is closed.)