By Eamonn Ryan
The regulatory breakthrough creates an opportunity.
The hardest part starts when the container leaves the cold store, but it also creates a demanding engineering challenge. For an in-transit treatment to work, the refrigerated transport system must do more than maintain a nominal setpoint. The fruit itself has to reach the required treatment temperature, and that temperature has to be maintained for the required period.
This is where the cold chain becomes considerably more than a logistics service. It becomes a controlled thermal process. The setpoint is not the fruit temperature – this distinction is fundamental.
A reefer controller may indicate that the air temperature is at the required level while the centre of the fruit remains warmer. The thermal mass of a fully loaded citrus container is considerable. Heat stored within the fruit, cartons and pallets has to be removed. Air has to circulate through the cargo effectively, and the coldest air in the container cannot simply bypass warmer areas of the load.
South African protocols for other export markets demonstrate how demanding this can become. For example, the current South African protocol for citrus exported to Korea specifies self-refrigerated treatment containers, temperature sensors with high accuracy around 0°C, automatic recording and carefully controlled loading to ensure uniform airflow around pallets and boxes.
The implication for India is straightforward. The reefer’s display is not the treatment record. The treatment record comes from the temperature sensors monitoring the fruit and the continuous data associated with the treatment.
Pre-cooling becomes critical
The most effective way to reduce the thermal burden on the reefer is to remove as much field and packing heat as possible before loading. Other South African cold treatment protocols illustrate the principle. The Thailand protocol, for example, requires citrus intended for in-transit cold disinfestation to be pre-cooled for at least 72 hours until the innermost fruit pulp reaches the required treatment temperature before container loading.
The precise Indian requirements must, of course, be followed once the final protocol is implemented. But the engineering principle is universal:
- The cold-treatment clock cannot simply be started because the container has been switched on.
- The fruit has to reach the required thermal condition.
- This puts pressure on the packhouse and cold-store interface.
A shipment can be perfectly refrigerated at sea and still fail to meet its treatment requirement if it entered the container too warm or was loaded in a way that prevented uniform cooling.
Airflow becomes a phytosanitary issue
This is where cold-chain engineering gets particularly interesting. In conventional refrigerated transport, airflow is essential for maintaining product temperature and quality. Under cold-treatment conditions, airflow becomes part of the phytosanitary control strategy.
Pallets and cartons need to be arranged to allow refrigerated air to move consistently through the load. South African cold-treatment protocols specify loading arrangements designed to promote uniform airflow, while fruit temperature sensors are positioned at representative points in the cargo.
The objective is to avoid cold spots and, more importantly, warm spots. A container in which the air temperature looks satisfactory but fruit in the centre of a pallet has not reached the treatment temperature is not a successful treatment system.
This places a premium on everything from container design and evaporator performance to airflow distribution, pallet configuration, carton ventilation and pre-cooling, while accurate sensor placement and calibration, together with continuous temperature recording, become equally critical. In this environment, the sensor becomes almost as important as the compressor.
There is an important technological shift here. For ordinary refrigerated transport, the refrigeration plant is the heart of the system. For regulated cold treatment, the measurement and verification system becomes equally important. A current South African cold-treatment protocol for Korea requires sensors with an accuracy of ±0.1°C around 0°C, automatic recording and hourly data capture, with recorded values protected against alteration.
Another South African in-transit protocol specifies continuous recording, multiple fruit-pulp sensors and the ability to retain and produce the treatment record for inspection.
The technology therefore creates a chain of accountability: Refrigeration → temperature → sensor → data → verification → phytosanitary clearance.
A refrigeration failure is no longer merely a quality problem. A sensor failure or questionable temperature record can become a market-access problem.
The ocean becomes part of the treatment plant
This is perhaps the most powerful way of explaining what has changed. Once in-transit cold treatment is permitted, the sea voyage is no longer simply the period during which the fruit is transported while refrigerated. It can become part of the treatment process.
South African citrus has already demonstrated the viability of this concept in other markets. In-transit cold treatment has been used for destinations including China, where specialised reefer vessels have carried citrus through the required treatment period before arrival.
The concept therefore isn’t new. What is new is its application to the South Africa–India citrus corridor. And that brings the story back to the container.
The container is simultaneously: packaging, warehouse, refrigeration system, treatment chamber, data recorder and phytosanitary evidence.
That is a remarkable amount of responsibility for a 40-foot steel box.