Movable rapid cooling has potential

CONTACT DETAILS: +27 21 880 2332/ +27 82 453 1040/
DURATION: One year
Lead institution: Aruba Cooling
Beneficiary: The table grape industry

About six years ago, Aruba Cooling developed the innovative concept of a moveable rapid cooling (MRC) unit, which is really a forced-air cooling tunnel on wheels. It would take cooling directly to the vineyard or orchard, potentially shortening the supply chain and reducing the carbon footprint. After successful initial trials at South African table grape farms, two MRC units were sold to an agricultural development company in Egypt. The technology was not commercially implemented in South Africa, since the fresh fruit industry with its long established fixed cold chain infrastructure required clear technical proof of MRC functioning.

Comparative cooling trials and fruit quality assessment

An MRC unit, able to cool ten pallets at a time, was built for test purposes. It was moved to The Pines, a table grape farm in the Hex River Valley, Western Cape. The Post-Harvest Innovation Programme financed a project in which the capability of the unit to comply with time and temperature protocol requirements was tested. Aruba Cooling conducted trials in conjunction with the South African Table Grape Industry (SATI). One white seeded (‘Dauphine’) and two black seeded (‘Barlinka’ and ‘Bonheur’) cultivars were packed in 4.5kg cartons, together with plastic liners, polycote and carry bags.

Ten pallets of table grapes were cooled at a time to -0.5°C by rapid forced-air cooling in the MRC unit, whilst the control batch was cooled in conventional fixed, forced-air cooling tunnels. Temperature probes were connected to sensors and loggers and inserted at representative positions inside the cartons in the MRC unit. Frequent sample readings provided cooling graphs and other relevant data.

Fruit quality was tested over a simulated export period of about eight weeks. Grape samples from the MRC unit and the control batch were measured for berry shatter, dry stems, weight loss and signs of decay. Test results of both methods were statistically analysed and compared to determine their effect on quality maintenance and whether they produced different outcomes.

Outcome of study

  • Test results indicated no significant differences between the technical functioning of the MRC unit and fixed cooling tunnels. It was unequivocally proved that the MRC unit is able to cool table grapes within 36 hours to -0.5°C, in compliance with export time and temperature protocols, and with no adverse effect on fruit quality,
  • However, there is no present local market acceptance for this product. It is not commercially viable to buy an MRC unit that will only be used during harvesting, whilst renting it adds extra cost due to the practical logistics involved in moving it around.
  • In terms of commercial viability, there are still opportunities for success. Countries like Chile, India and Madagascar indicated interest and some South African producers would rent MRC units if they were operated in a fleet. Aruba Cooling is looking into these possibilities, with a new business model.
  • Ultimately, MRC technology is a good South African innovation that could provide additional cooling capacity during peak harvesting times and reduce the number of handling links in the cold chain.
  • It is suitable for all deciduous fruit and vegetables – an MRC unit is currently being tested in the Western Cape on vegetables.