SATI Beyond The Bunch 3rd Quarter 2025

Bunch carriers Pre-packaging grapes in bunch carriers is con venient for retailers and consumers. However, bunch carriers can impede airflow, especially if their perforated area – the total area of the perforations as a percentage of the total liner area – is too small or stickers or labels cover the perforations. If the bunch carrier is poorly ventilated, the SO 2 reaching the bunch may be insufficient to con trol decay. Inadequate airflow will also hinder cooling and increase humidity, elevating the risk of condensation during cold-chain breaks. Dr Mduduzi Ngcobo’s doctoral research found significantly faster cooling of bunches in open top or clamshell punnets compared with carry bags. He speculated that the soft carry bags deform, allowing the liner to collapse and cold air to channel between the liner and the carton, rather than move through the liner perforations. The rigid punnets, on the other hand, press the liner against the carton sides, creating less op

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The bunch It’s worth remembering that berries and stems are packaged naturally – they are covered in epidermis and a cuticle. These outer layers limit water loss and repulse invading pathogens. Differences in skin and cuticle char acteristics impact the optimal choice of man-made packaging for each cultivar. Berries lose water more slowly than stems because berries have a less water-permeable surface and a smaller surface-to-volume ratio. Therefore, cultivars with relatively more stem area or more exposed stems – looser bunches – will be more sensitive to moisture loss. Unfortunate ly, their stems are also more visible, so any desiccation or browning is easier to spot.

portunity for cold air to bypass the liner. Although table grapes in punnets were better ventilated, they didn’t lose significantly more mass than those in carry bags during a 35-day storage period. However, bunches in punnets did have more stem de hydration, especially in the open-top punnets. It should be noted that Ngcobo didn’t use forced-air cooling in his trials. Forced-air cooling would likely have improved ventilation and cooling rates of the carry bags. The perforated area of liners was also smaller than current industry standards – more on this below. An industry-funded project led by Dawie Moelich investigated the rela tionship between vents in punnet lids and the development of decay. The results confirmed that poor ventilation of the punnet led to insuffi cient SO 2 levels and increased decay. Moelich demonstrated that a minimum total lid vent area of 15 cm 2 for 500 g punnets and 7.5 cm 2 for 250 g punnets reduced decay during cold storage. Vents are less effective when confined to the edges of the punnet lids. SO 2 is about twice as heavy as air, so it tends to sink rather than move sideways. Therefore, vents in the top of punnet lids improve SO 2 penetration.

Sheets Moisture- and shock-absorbing sheets and SO 2 sheets can reduce ventilation, especially if they block perfora tions or holes in other packaging components. However, the SO 2 sheet should be large enough to distribute SO 2 evenly over all the bunches. Moisture- and shock-absorbing sheets also lower humidity and can reduce SO 2 levels. When placed above the SO 2 sheet, the moisture-absorbing sheet will have a greater effect on moisture. When placed below the SO 2 sheet, it will have a greater effect on SO 2 levels.

BEYOND THE BUNCH • 8 • QUARTER 3 • 2025