What Is Reefer Shipping and How Does It Work?

Reefer shipping is the transport of temperature-sensitive cargo in refrigerated containers, known as reefers, that plug into a vessel's power supply and hold a set temperature for the entire voyage. You need it whenever your cargo would spoil, degrade, or lose value outside a narrow temperature band — chilled or frozen food, pharmaceuticals, flowers, and similar goods. If your product is shelf-stable at ambient temperature, standard dry containers are cheaper and simpler; reefer shipping only pays off when temperature control is non-negotiable.

What Reefer Shipping Is and What It Carries

A reefer is a container with an integrated refrigeration unit (the "machinery" end) that connects to the ship's electrical grid. Unlike a dry container, it actively manages temperature, and on many units also ventilation and humidity, for the whole journey — not just at the terminal.

Typical reefer cargo:

• Perishables — fruit, vegetables, meat, seafood, dairy
• Pharmaceuticals — products requiring a validated temperature range
• Flowers and plants — highly sensitive to heat and ethylene buildup
• Other temperature-sensitive goods — certain chemicals, cosmetics, and specialty foods

The key distinction is chilled versus frozen. Chilled cargo (often roughly −1°C to +15°C depending on the commodity) is kept just above freezing to slow ripening and decay. Frozen cargo is held well below 0°C to keep it solid. The exact setpoint depends on the commodity, not on a single universal number, so always confirm the required range with your buyer or supplier.

How the Reefer Process Works

1. Booking and equipment selection

You book a reefer container with the carrier and specify the commodity, required temperature, and any ventilation or humidity needs. The carrier assigns a reefer unit and confirms the setpoint. Getting this wrong at booking is the most common source of downstream problems.

2. Pre-cooling the cargo

The cargo itself should be pre-cooled to its target temperature before it is loaded. A reefer is designed to hold temperature, not to pull a warm load down to setpoint quickly. Loading warm cargo forces the unit to work hard, can cause hot spots, and risks spoilage.

3. Loading and sealing

The container is loaded, typically leaving space for air to circulate around the cargo. Blocking airflow is a frequent mistake — air must move through and around the load for even cooling. The unit is then set and the container sealed.

4. Monitoring in transit

Once on the vessel, the reefer plugs into the ship's power and runs continuously. Temperature is monitored, and many carriers provide data logging so you can see the temperature history. This record matters if a claim arises.

5. Delivery and discharge

At destination the container is discharged, kept powered at the terminal, and moved to the consignee. The cold chain should remain unbroken from origin to final delivery — any gap, such as an unpowered wait, can damage the cargo.

Key Requirements to Get Right

Common Mistakes and How to Avoid Spoilage or Claims

• Loading warm cargo. Pre-cool first; the unit cannot reliably pull down a warm load.
• Packing too tightly. Leave space for air circulation, or you get uneven temperatures.
• Wrong setpoint or ventilation. Confirm the exact requirement for your specific commodity rather than assuming a generic number.
• Broken cold chain at handoffs. Ensure the container stays powered during terminal waits and inland moves.
• No monitoring record. Keep the temperature log; it is your evidence if something goes wrong.
• Assuming all reefers are identical. Capabilities for ventilation and humidity vary, so state your needs at booking.

If you handle temperature-sensitive cargo, the practical rule is simple: confirm the commodity's required temperature, ventilation, and humidity before booking, pre-cool the cargo, protect airflow, and keep the cold chain and its records intact from origin to delivery.