Keeping it cool: An overview of reefer containers

From juicy strawberries to life-saving vaccines, have you ever wondered how these and many other temperature-sensitive commodities are kept fresh and safe while travelling long distances?

Enter the reefer container – essentially the world’s de facto mobile fridge-freezer. And the reason we can all enjoy quality, fresh perishable products shipped to us from across the world.

Up ahead, we explore the fundamentals of reefer containers, how they work, and best practices to ensure products are kept safe during transit.

What are reefer containers?

Reefer containers, or refrigerated containers, are specialised shipping containers designed to transport various types of reefer cargo, such as fresh produce, frozen foods, pharmaceuticals, and other temperature-sensitive goods.

These containers are equipped with insulated walls, a state-of-the-art refrigeration unit, humidity control, and a fresh air exchange system – just to mention a few key features.

The reefer container and specialist software installed in the controller will accurately maintain perfect temperature and humidity levels throughout the journey. This prevents spoilage and other forms of deterioration, ensuring that goods arrive at their destination in optimal condition.

Differences between dry and reefer containers

The key difference lies in their ability to control the internal environment of the container.

While dry containers provide a basic, unprepared space for non-perishable items, reefer containers offer a controlled environment to preserve temperature-sensitive cargo. This makes them indispensable for transporting fruits and vegetables, pharmaceuticals, and other types of refrigerated cargo , where temperature stability is directly tied to product integrity.

Types of reefer containers: Dimensions, sizes, and specifications

Reefer shipping containers have various sizes and configurations, specifically designed to cater for different cargo requirements and transport routes. They usually come in standard container sizes of 20ft or 40ft high cube containers.

• 20ft reefer containers are ideal for smaller volumes of temperature-sensitive cargo and are often used for urban or regional deliveries due to their compact size. They are also widely used in ocean transportation, especially when smaller shipments need to be consolidated or when vessel space is limited.
• 40ft HC reefer containers are best for large-scale transportation, ideal for high-demand routes with larger cargo loads like fresh produce or seafood. In today’s market, 40ft HC reefer containers account for over 90% of the volume moved in reefer containers globally.

For example, Maersk provides the following types of refrigerated container:

How do reefer containers work?

Refrigerated containers are engineered to create and maintain optimal conditions for temperature-sensitive cargo — ensuring specific temperature, humidity, and airflow levels during transit. This process depends on advanced refrigeration technology, efficient power systems, interior design of container, and more.

Cooling system mechanics

The heart of a reefer container is its cooling unit — which comprises a compressor, condenser, evaporator, and refrigerant.

The compressor compresses refrigerant gas into a high-pressure liquid, which is then passed through the system. Once the compressed refrigerant enters the evaporator, it expands and evaporates, creating a cooling effect. The heated gas flows into the condenser, where it’s cooled back into a liquid, ready to be cycled again. This continuous loop maintains the set temperature within the container.

Airflow and temperature distribution

Reefer containers use a bottom-air delivery system. Depending on the cargo type and packaging used, the air is circulated along the floor of the container and upward. This ensures all areas within the container are evenly cooled.

Advanced monitoring

These containers are also equipped with sensors that monitor temperature, humidity, and air composition in real-time. Some of the most sophisticated remote container management systems even alert users to any deviations from the set parameters. This gives customers complete visibility of their cargo from origin to destination and allows for prompt corrective actions to safeguard the cargo, if needed.

Managing reefer containers: Controlled atmosphere, humidity, and typical temperatures

Controlling the atmosphere surrounding temperature-sensitive cargo is critical to preserve the quality and freshness of certain commodities benefitting from this.

Atmosphere management, or controlled atmosphere, refers to the process used in reefer containers to control the internal air composition and humidity, particularly the levels of oxygen and carbon dioxide. By creating an optimal atmosphere, reefer shipping containers help maintain the shelf life of sensitive cargo types, prevent spoilage, and preserve freshness.

A major aspect of reefer technology, atmosphere management serves two key functions:

• Controlled atmosphere (CA): Reefer containers utilise CA technology to regulate gas levels within the container. This helps to slow down the ripening process of fruits and vegetables, extending their shelf life and reducing food loss.
• Humidity control: Reefer containers prevent damage to moisture-sensitive items like pharmaceuticals and confectionary by removing humidity from the surrounding air.

With the ability to control temperature and atmosphere conditions precisely, businesses can maintain the integrity and quality of their perishable goods even when transporting them long distances.

What is the temperature range of a reefer container?

Temperature requirements for different types of cargo vary significantly. Here are some examples:

• Fresh produce: Fruits and vegetables require a chilled environment, typically between 0°C to 13°C depending on the product. For instance, leafy greens stay fresher closer to 0°C, while citrus fruits may be kept at a slightly higher temperature.
• Frozen goods: For frozen produce, including seafood and meat, temperatures are generally set at or below -18°C to maintain quality. Ice cream, which is particularly sensitive to temperature deviations, may require even colder settings, around -25°C. For cargo requiring ultra-low temperatures, like certain seafood and biologics, reefer containers able to provide ultra-low temperatures (down to -60°C) can be used.
• Pharmaceuticals: Many medications are stored within a narrow temperature range, mainly between 2°C and 8°C, to ensure efficacy. Specific items, like vaccines, may need even tighter control with real-time monitoring for compliance and safety.

Tip: For more on the different types of goods transported in reefer containers, read Keeping it fresh: An overview of refrigerated cargo.

Using reefer containers: Challenges and best practices

While reefer shipping containers offer a reliable solution for transporting perishable goods, they also present certain challenges.

Common challenges in reefer container operations

• Equipment malfunctions: Reefer containers rely on their cooling units, and any mechanical issues can risk the entire shipment. Faulty refrigeration systems, power outages, or compressor malfunctions can lead to temperature fluctuations that may jeopardise product quality.
• High operating costs: Reefer containers are more expensive to produce and procure compared to standard dry containers. They also have higher operating costs for the owner, as they require inspections, cleaning, and regular monitoring and equipment upgrades.
• Complex logistics: Using reefer containers requires meticulous planning, especially when transporting items across multiple climates and regulatory environments. Each transition point presents potential risks and requires coordination to keep containers powered and within the correct temperature range.

Best practices for optimal reefer container usage

• Regular maintenance and inspections: Preventive maintenance is essential to ensure that reefer units function properly. Components must be inspected on a per-trip basis. Service providers adopt maintenance systems to address potential issues early to reduce the risk of malfunctions during transport.
• Efficient loading and unloading practices: Minimise the time that reefer doors are open during container stuffing and destuffing. Quick, efficient handling ensures that temperature fluctuations are kept to a minimum, which is particularly important for highly temperature-sensitive goods like pharmaceuticals or ice cream.

Ready to explore shipping refrigerated cargo?

Did you know that Maersk transports an extensive range of temperature-sensitive commodities globally? Whether you are shipping cherries from South America or flowers from Kenya, our cold chain logistics solutions and end-to-end integration capabilities will ensure your refrigerated cargo arrives in tip-top condition.