27 July 2021 • 18 min read
Reefer Shipping: A Guide to Shipping in Refrigerated Containers
What is a reefer? Learn about reefers, types, and techniques for shipping temperature-sensitive perishables in refrigerated containers.
Reefers (short for refrigerated containers) are large temperature-controlled containers used to transport perishable cargo such as fresh fruits and vegetables, seafood, meat, dairy, flowers, pharmaceuticals, photographic film, and several chilled and frozen goods that might spoil if not maintained at the right temperature and humidity. Reefers are the only effective way to transport perishables and other temperature-sensitive commodities in large quantities across long distances. This blog serves as a complete guide to reefers and touches on the following aspects:
- How reefers work
- Benefits of reefers
- Types of reefers
- What kind of cargo is shipped in reefers?
- Components of a refrigerated container
- Right way to handle reefer cargo
- Dos and don’ts
How Reefers Work
Reefers distribute chilled air from the floor via T-shaped decking. As such, they are also called “bottom air delivery units”. This design ensures the container produces a steady flow of air powerful enough to maintain the required temperature for the duration of the transit, even under the harshest conditions. Reefers are also equipped to provide warmer temperatures, irrespective of the temperature outside. They have a temperature range of -35 degrees Celsius to 35 degrees Celsius.
The biggest difference between reefers and conventional containers is the temperature control function. Normal containers are used to ship dry goods and do not have or need such a system. The two also differ in terms of size, design, power generation and electrical distribution equipment. Reefers are smaller and contain individually powered refrigeration units. They cost around six times more than a conventional container because they come with additional insulation and a power plant.
Benefits of Reefers
- Because they are self-contained refrigerated units, they can bypass cold storage on arrival at the destination port
- They are available in many dimensions, making them ideal for road, sea and air transportation
- They are durable and can operate in inclement conditions
- They offer a better return on investment than reefer ships
- They help avoid wastage of perishables, extend the shelf life of goods
- They provide easy loading and unloading, which is why container ships are now built or redesigned to carry reefers
Types of Reefers
Different types of reefers are available in the market today. Depending on efficiency, purpose, cargo and your requirements, one or the other can be used.
- Closed reefer: This is a conventional reefer that comes in a single piece. It has an integral front wall and all-electric automatic cooling and heating units
- Modified Atmosphere/Controlled Atmosphere (MA/CA) reefers: These are insulated containers with an air exchange system that keeps the atmosphere constant by replacing the consumed oxygen. As such, the atmosphere in these containers is in equilibrium with the deterioration rate of the cargo.
- Automatic Fresh Air Management (AFAM) reefer: This container uses cutting-edge technology to automatically adjust air exchange within the container to maintain a constant temperature. Similar in its working to the MA/CA reefer, the AFAM reefer controls the composition of oxygen, carbon dioxide and other gases. Its controls can be adjusted to extend the shelf life of cargo, irrespective of outside conditions.
Reefer dimensions can vary. Tabled here are the standard ones:
Know Your Cargo
While reefers transport a variety of goods, different products must be shipped under different conditions to ensure their freshness on arrival. Reefer cargo falls into three broad categories:
- Chilled goods: These include fresh fruits and vegetables, seafood, dairy, eggs, confectionery, live plants and flowers. They require low temperatures, around freezing points, but are not to be frozen. Their freshness and shelf life depend greatly on their nature and surrounding conditions. Temperature settings for such produce must factor in the stage at which the crop is being shipped. They must be transported with utmost precision so as to retain their commercial value. For example, asparagus and broccoli have high respiration rates and so, release a lot of gases and moisture. They require optimum temperature and humidity levels so that their quality and shelf life are not impacted.
- Frozen goods: These are goods that need to be stored and transported at temperatures of -20°C and below, which means they are frozen solid. Ice-cream, frozen meat, poultry and seafood, concentrates and prepared foods are some examples. The freezing temperatures prevent spoilage and help retain flavour, aroma, texture and quality. They stop disease-causing bacteria and microorganism growth while also slowing down enzyme activity and oxidation. For such goods, the reefer must maintain freezing temperatures without fluctuations. Repeated freezing and thawing can result in mushy products.
- Special and miscellaneous cargo: These constitute non-food products that require optimum temperature and humidity. Pharmaceuticals and drugs form the majority of such cargo. Tobacco, batteries, chemicals and photographic film also come under this category. Quite often, they have special handling instructions for packaging, stowage, temperature and humidity control.
Reefers remove heat generated by the “respiration” of products, thus keeping temperatures stable. They also control humidity to maintain conditions favourable to the cargo. But how does a reefer do this? Let’s look at the reefer components that fulfil these key functions:
- Genset: A genset, or generator set, is the reefer’s power source. It is usually dual-powered, which means it runs both on fuel (diesel, petrol and gas mostly) and electricity. This ensures it can tap the power unit of a ship or operate on fuel while on a truck. The genset can be clipped to the side of the container (clip-on genset) or mounted on the chassis of the container from the bottom (underslung genset).
- Humidity control: The relative humidity of air in a reefer is critical to the safe transportation of cargo. (Relative humidity is defined as “the amount of water vapour in air expressed as a percentage of the amount needed for saturation at the same temperature”.) Dry air can cause excessive water loss in fruits and vegetables while moisture in the air can cause mold and bacteria. A reefer’s humidity control mechanism maintains optimum humidity conditions for goods such as pharmaceuticals and electronics. It ensures dry packing and prevents fungi and rotting in the case of consumables. A reefer has a dehumidification range of 60% to 95% maximum relative humidity in the chilled temperature range.
- Temperature control: Reefers are either water-cooled or air-cooled, though water coolant systems are dwindling because they are expensive. Air cooler fans, either propeller or centrifugal type, remove dissipated heat from the refrigeration unit. A compressor, powered by a small engine, draws in refrigerant gases and compresses and liquefies them. This releases heat in the surrounding air. The air flows into a condenser and then into an evaporator, which drains the heat outside.
- GPS chip: A reefer comes equipped with a GPS chip to ensure no package is lost in transit. Typically, containers enter multiple ports and use several transportation modes before they arrive at their final destination. Cargo security is paramount. And the GPS chip provides the location and temperature status of each container.
Right way to handle reefer cargo
Cargo must be handled properly at every step of the transportation process, from packing to stowage to processing. Negligence can adversely impact the shelf life, quality and appearance of the cargo. It is important to factor in equipment type, product quantity and weight, transit duration, and international regulations. Here are the different cargo handling stages and the right way to do it:
- Pre-shipment handling: The importance placed on pre-shipment handling implies that a shipper must provide accurate information of the products being shipped, their volume and weight, departure and destination ports, type of packing (boxes, drums, palettes, etc), temperature and humidity requirements, and any other handling specifics. The freight forwarder usually handles the rest, such as identifying the right vessel and container, coordinating shipment dates, ensuring cargo size and weight are within legal limits and that the conditions are right.
- Pre-cooling: Reefers do not lower the temperature of goods. Rather, they maintain the pre-cooled temperature of goods. So, the shipper must ensure his chilled or frozen goods are pre-cooled to the recommended temperature before they are stuffed into the container. Likewise, the container has to be pre-cooled to prevent surface thawing and freezer burn, which happens when the container and cargo temperatures don’t match. For loading, a “cold tunnel” facility is used. This comprises a tightly insulated duct that prevents warm, humid air from entering the container.
- Packaging and stowing: This aspect of cargo handling should be designed to protect against rough handling and bad weather. The cartons used for packing must be strong enough to withstand the weight of the stacks above them and capable of protecting the products inside, especially with regard to humidity and temperature. When stowing cargo, there should be adequate ventilation and airflow. However, different cargo types require different stowage practices. Chilled fruits and vegetables need proper air supply through the packaging while frozen goods must be stacked as solid blocks without gaps.
Best Practices in reefer shipping
Proper storage and stowage cut the risk of spoilage and rejection at the destination port. Here are the dos and don’ts of reefer shipping:
- Tightly pack cargo and ensure it is stable
- Set the reefer at the prescribed temperature and humidity settings
- Pre-cool the cargo when necessary
- Ensure proper ventilation and correct settings
- Insure your cargo, because a lot can go wrong with a reefer as compared to a conventional container
- Stow the cargo above the load line marked in red
- Stow the cargo further than the end of the T-floor
- Allow restrictions or tight stuffing that block airflow
- Pre-cool the reefer if it is not in cold storage
- Allow gaps between pallets and the door
- Miss shipment deadlines and cutoffs, particularly for perishables.
TABLE: Temperature and humidity settings for different commodities
*MA = Modified Atmosphere. *CA = Controlled Atmosphere
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