A cool journey for fresh Avocados

A hot summer’s day in Veracruz in Mexico: the thermometer climbs above 40°C in the shade, and the air in the port shimmers under a blistering sun. Notwithstanding the heat, several snow-white reefer containers are being loaded onto Hapag-Lloyd’s “London Express”. Inside the containers: a wintry 5°C and several tonnes of avocados. The fruit, which frequently originates in Mexico but which is also grown in South Africa, Peru and Chile, often spends several weeks on board ships as it makes its way to Northern Europe. But how do the reefer containers ensure that this low temperature is kept constant and remains unaffected by the outside temperature until they reach their port of destination?

Fresh Avocados often spend weeks travelling to Europe after they are harvested.

“A reefer works in exactly the same way as a fridge, even if a 40-foot container has a volume of more than 67,000 litres while a fridge only has between 100 and 200 litres,” explains Frank Nachbar, Director Container Engineering at Hapag-Lloyd. The principle: “A substance needs energy to change from a liquid into a gas. In the case of a reefer container, in the form of heat from the air inside the container. For the reverse process – condensation – this energy is released back into the outside air,” he explains. In Hapag-Lloyd’s reefer containers, the substance in question is the cooling agent that moves within a closed circuit inside the cooling unit.

Using sensors, the Reefer controls the refrigeration circuit, as well as the heating facilities if necessary.

When the reefer container is in operation, the gaseous cooling agent is concentrated in a compressor and then condensed into liquid form by a heat exchanger. The superfluous energy created by the process is released into the outside air. The liquid cooling agent is subsequently decompressed via an injection valve and turns to gas again in an evaporator. This requires energy, which is drawn from inside the container in the form of heat, thus cooling the container. The compressor keeps this circuit in continuous motion. “You could call it the heart of the reefer,” says Frank Nachbar. A controller, which acts like a small computer, monitors and controls the operation. The required temperature programmes are set here before transportation. Using sensors, it then controls the refrigeration circuit, as well as the heating facilities if necessary. These are used if the outside temperature is lower than the temperature required inside the container.

A controller, which acts like a small computer, monitors and controls the operation of the Reefer.

For avocados, however, this is in itself not enough. They are classed as a “breathing” fruit that ripens particularly quickly and, even if it is kept cool, begins to spoil after three weeks. However, since its journey to the customer often takes longer than this, the reefer has to slow down the fruit’s ripening process in a controlled manner. To enable this, the composition of the air in the container is regulated – “controlled atmosphere” is the name of this system.

By lowering the level of oxygen and increasing the carbon dioxide content inside the container, the fruit is almost unable to “breathe” and therefore falls into a “ripening sleep”. The reefers, which are equipped with “Extrafresh” technology, use sensors to continuously measure the proportion of oxygen and carbon dioxide and ensure that ideal air composition is maintained by means of a membrane and automatic fresh air ventilation. This technology has enabled Hapag-Lloyd to increase the maximum transport time for avocados to up to 35 days – two weeks longer than would be possible without this technology.

Incidentally: in extreme circumstances, the high-tech container would even be able to maintain the interior temperature at up to minus 40°C – even if the outside temperature was up to plus 45°C. In the case of the avocados from Mexico, however, such extreme refrigeration was not requested. The fruit only needs a comparatively mild 5°C to ensure that it is fresh when it reaches our customers.

Would you like to find out more about what Hapag-Lloyd’s reefer containers can do? Just click to have a look on our reefer page.