SATI Beyond The Bunch 3rd Quarter 2025

Liners

Liners are essential to curtail moisture loss from bunches. However, unperfo rated liners slow cooling and increase humidity, predisposing the grapes to all the problems already discussed. For example, Stefan du Plessis’ mas ter’s research showed that an unper forated liner reduced stem browning but increased SO 2 damage in Red Globe. The unperforated liner also increased berry split and promoted decay in Thompson Seedless. The solution is perforating liners so that they restrict but don’t prevent venti lation. The optimal perforated area differs from cultivar to cultivar. Ngcobo measured the ventilation in cartons with unperforated, microper forated, and perforated liners. He in cluded three perforated liners: 54 x 2 mm, 36 x 4 mm and 120 x 2 mm. The liners contained Regal Seedless grapes in carry bags, shock-absorbing sheets, moisture-absorbing sheets, and SO 2 -re lease systems. Cooling rates were similar for unper forated and microperforated liners, probably because Ngcobo didn’t include forced-air cooling, limiting airflow through the microperforations. He also didn’t see a significant dif ference in cooling time between the different perforated liners. However, at the time he was conducting his trials, the total perforated area of lin ers used by the South African industry was much smaller than it is today. For example, current SATI-funded trials on packaging are testing 96 x 5 mm, 112 x 4 mm, and needle-scarred micro perforated liners.

Ngcobo reported that the relative humidity inside the perforated liners corresponded to that of the cooling air. Lower humidity inside perforated liners helped prevent condensation. A related paper by Dr Mulugeta Delele and co-au thors described the modelling of airflow and heat transfer in table-grape packaging. They reported that partial or complete cooling of bunches, either as bulk grapes or in carry bags, before placing them in liners, greatly reduced total cooling time. Partial cooling before placing the grapes in an unper forated liner achieved a high relative humidity without SATI

subsequent condensation. For perforated liners, mois ture loss can be limited by maintaining a high relative humidity of the cooling air. Marius Leuvennink and Dawie Moelich, while at Ex periCo, researched grape cooling in a forty-pallet commercial cooling tunnel. They reported that grapes in 4.5-kg cartons cooled nearly 38% faster in 36 x 4 mm liners than in unperforated liners. Cooling times in 9.0-kg cartons were more than 35% faster in 36 x 4 mm liners than in unperforated liners.

BEYOND THE BUNCH • 9 • QUARTER 3 • 2025