Perforation options for shipping cartons for overseas transport of tropical and subtropical fruit [German version]

- by Dr. R. Scharnow -


1. Background


Tropical and subtropical fruit, such as citrus fruit, bananas and pineapples, are highly perishable commodities, which require uninterrupted cooling from the consignor to the consumer if they are to arrive intact. Due to their vigorous metabolic processes, they require

optimum cooling temperatures, in order to inhibit metabolic processes while also avoiding chilling damage;
optimum relative humidity values in order to prevent mold and rot due to excessive moisture, while also preventing wilting, shrinkage and weight loss due to drying-out;
optimum gas composition of the cold store atmosphere, which must firstly supply oxygen in the fresh air and secondly dissipate harmful substances such as carbon dioxide and ethylene;
optimum packaging and stowage in order to avoid bruising and to ensure that the cooling air can flow properly through and around the packages.



2. Packaging


Chilled goods are usually packaged in cartons and crates for international maritime transport. The cartons are primarily made from corrugated board, with the lid part generally consisting of single wall corrugated board and the base part of double wall corrugated board for greater strength. They may also be provided with a water-repellent finish (by waxing, coating or impregnation) to prevent moisture absorption.

Since corrugated board is used instead of millboard, the tare for citrus fruit shipping cartons, which have a capacity of 18 to 22 kg, is on average 1000 g. Using single wall corrugated board for the lid part instead of the double wall corrugated board used for the base part reduces the tare weight, for example achieving a weight saving with folding telescope cartons of 240 g for mandarins from Uruguay, of 280 g for oranges from Uruguay and of 150 g for bananas from Ecuador (see table).

Product Exporting country Packaging container Packaging material Tare, lid Tare, base Total tare Perforation
content
Mandarins Uruguay Folding telescope carton Corrugated board 400 g 640 g 1040 g 2.15%
Oranges Uruguay Folding telescope carton Corrugated board 500 g 780 g 1280 g 2.13%
Lemons Spain Folding carton Corrugated board     900 g 7.87%
Bananas Ecuador Folding telescope carton Corrugated board 450 g 600 g 1050 g 8.18%


Perforated polyethylene bags are often used as inner packaging and/or the fruits are wrapped in paper, e.g. pears from Brazil wrapped in sulfate paper, and shaped trays are often also used to separate the fruit into layers (e.g. apples and pears from Brazil).


3. Perforation


Vertical air flow has increasingly been superseding horizontal air flow in refrigerated holds as the path through the cargo is around ten times shorter than for horizontal air flow, so resulting in uniform temperature stratification in the cargo. The carton perforations play a vital role as they must ensure that air also flows through and around the packages.

Figure 1 illustrates vertical air flow through perforated cartons, a vital point being that the perforations in the stacked cartons stowed athwartships must correspond exactly so that the air can flow vertically through all the cartons. This is also the reason why the perforations are in most cases arranged directly opposite each other.

Diagram, air flow Figure 1: Vertical air flow through
perforated cartons



The following diagrams illustrate the usual kinds of perforations.

a) Plan view b) Side face c) End face

Figure 2: Folding telescope cartons for mandarins; lid part


In the folding telescope carton (Figure 2), the lid part is provided with a slot between the flaps and six round perforations, each 2.5 cm in diameter, arranged in opposing pairs. The side and end faces each have two perforations, with the end face perforations being somewhat lower than the side face perforations (see Figures 4 and 6).

d) Internal view e) Side face f) End face

Figure 3: Folding telescope cartons for mandarins; base part


The inner flaps of the base part closely abut, but the six perforations ensure adequate vertical air flow. The diameter of the holes is 3 cm on the inside, as opposed to 2.5 cm on the outside. The side and end faces each have two elongate 3 cm x 5.5 cm openings.

The proportion of the total surface area of the closed folding telescope carton occupied by perforations amounts to 2.15%. While the lid part consists of single wall corrugated board, the base part is made from double wall corrugated board and is coated on the inside and outside with a water-repellent finish.

a) Plan view b) Internal view c) Side face d) End face

Figure 4: Folding telescope cartons for oranges; lid part


e) Side face f) End face

Figure 5: Folding telescope cartons for oranges; base part


The lid and base parts of the folding telescope carton (Figures 4 and 5) are of the same design as in Figures 2 and 3, except that the central holes each have a diameter of 2.5 cm on the inside and the outer pairs of holes are each of a diameter of 3 cm. The side faces are each provided with three round holes of a diameter of 2.5 cm, while the end faces each have two such holes. These latter holes each correspond to elongate 3 cm x 5.5 cm openings. The proportion of the total surface area of the closed folding telescope carton occupied by perforations amounts to 2.13%.

The lid part is again made from single wall corrugated board and the base part from double wall corrugated board.

a) Plan view b) Side face c) Bottom surface d) End face

Figure 6: Folding cartons for lemons


The folding carton is optimized for vertical air flow (Figure 6). In this case, the outer and inner flaps leave an opening of an area of 528 cm² and the six 2.5 cm diameter holes have been located at the edges between the side and bottom faces. The base is of the same design as in Figure 2. The end faces have been perforated in such a way that the holes may be used as a handle (5 cm x 8 cm). The corrugated board is double walled, but since it is not a folding telescope carton, the tare is still only 900 g. Due to the large opening, the proportion of the total surface area of the folding carton occupied by perforations amounts to 7.87%.

a) Plan view b) Side face c) End face

Figure 7: Folding telescope carton for bananas


A similar principle has also been used for the folding telescope carton for bananas (Figures 7 and 8); the outer and inner flaps of the lid and base parts respectively leave an opening of 280 cm² and 220 cm² in area, so that vertical air flow is not impeded. In addition, the bananas packaged in perforated polyethylene bags (Figure 9) may be easily checked for ripeness. The side faces each have four oblong perforations of 1.5 cm x 6 cm and the end faces each have a handle-type opening of 3.5 cm x 10 cm and a further two holes 3.5 cm in diameter. The proportion of the total surface area of the closed folding telescope carton occupied by perforations amounts to 8.18%. The lid part consists of single wall corrugated board and the base part of double wall corrugated board.

(Click on Figures 8 and 9 to enlarge them)


Photo, banana carton

Figure 8: End face of a folding telescope cartons
for bananas from Ecuador

Photo, banana carton Figure 9: Bananas packaged in perforated
polyethylene film


Special cartons are used to transport pineapples from Martinique; these cartons have cardboard inserts which separate the individual fruits, so making an allowance for their high susceptibility to bruising. The base is lined with, for example, wood wool in order to prevent "pressure sores" on the fruit. Perforations are provided in the side walls and lid to allow proper air flow.