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Post harvest handling of melons | AG0241 |
Rob Dimsey, Bairnsdale
March, 1995 |  |
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Melons such as cantaloupes, honeydews and musk melons (arls melons from Japan) are highly perishable and only have a storage life of several weeks. In order for fruit to arrive at their destination in peak condition and with the longest shelf life, top quality fruit must not only be grown but must be given the best possible post harvest handling. Correct post harvest handling slows ripening and breakdown of the fruit increasing shelf life.
What controls post harvest quality
The major factors influencing outturn quality and shelf life of melons include: temperature, handling methods, disease control, packaging and presentation. The end result can only be as good as the weakest link in the chain.
Temperature control
Temperature is a vital factor in fruit quality. Every 10°C rise in fruit temperature leads to an increase in respiration by a factor of 2-3 times. This hastens ripening, increases moisture loss reducing quality and storage life. Ideally fruit should be packed and cooled to the holding temperature in less than 24 hours.
Harvesting
Melons are best harvested in the cool of the morning, especially for fruit destined for export or long term storage. Once harvested the fruit should be kept cool (not below 2°C for rockmelons and 7°C for honeydews) and ideally, either pre-cooled or held in a cool room. At the very least the melons must be left in the shade prior to packing.
Gentle handling is also essential. Melons are easily damaged and bruised, which can provide ideal sites for infection and fruit breakdown. The fruit should be gently placed into buckets or onto conveyors and not dropped or thrown. Melons left resting on rough surfaces will become indented under their own weight.
To obtain consistent fruit maturity frequent picking is important. Over mature fruit does not carry well, even after the best post-harvest treatments.
Pre-cooling removes field heat
To maximise storage and shelf life it is important to remove the field heat as quickly as possible. Room cooling is not effective as it is too slow. Before grading and packing, the fruit should be cooled to at least 15°C within 8 hours of harvest. The melons can be pre-cooled prior to grading and or immediately afterwards.
The most effective methods of pre-cooling are forced air cooling or refrigerated hydrocooling (the latter is expensive to install and operate). These methods provide rapid pull down times and can handle large quantities of fruit. A cheaper but less effective pre-cooling method is to shower the melons with evaporatively cooled water. This will lower the fruit temperature to the dew point and remove much of the initial field heat. This procedure is more suited to inland areas of low humidity.
Washing the melons
After picking and cooling, the fruit should be washed to remove soil and debris. Soil and debris can strip out or remove the fungicide from solution reducing the dips effectiveness.
Washing can be done prior to grading, via an inline spray or bulk dip as indicated in the grading line layout (Fig. 1). It is important to keep the wash water separated from the fungicide solution to prevent dilution and contamination of the dip.
Figure 1. Inline spray or bulk dip
Post harvest fungicide dips
Post harvest fungicide dips are essential to control post harvest diseases during storage, or long distance transport. The current fungicide recommendation is a mixture of benomyl (Benlate ) and guazatine (Panoctine ) both at 500 ppm.
- The benomyl should be mixed to a paste then stirred into the tank followed by a nonionic wetter (0.01 %).
- The guazatine should then be added and thoroughly mixed. Benomyl and guazatine are compatible only if mixed in this way.
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Agitation of the dip is essential, as fungicide can be stripped out of the solution by dirt particles and settle to the bottom of the tank. Bubbling air through the tank is one simple method of agitation. The dip should be topped up regularly to replace lost fungicide. This could be done automatically via a header tank or manually by changing the mixture, when the volume of fruit that has passed through is equivalent to 100 times the volume of the dip.
The grading line
Even grading for size and maturity is important for a quality pack out of melons. A range of graders are available such as rotating bar, rope, belt and weight graders. Melons like any other fruit require gentle handling. Because the melons vary from round to oval shapes a rope grader is a very effective, gentle and relatively inexpensive grader.
The layout of the grading line will vary depending on whether the fruit are to be conveyed along under sprays for washing and fungicide treatment or bulk dipped prior to grading. Inline brushes are very useful, fulfilling a number of functions. They assist in removing dirt by either dry brushing or in conjunction with an inline wash. Brushes also assist in ensuring good fungicide coverage of the fruit as well as removing excess moisture. However if the melons are not kept moving forward, brushes will abraid and cause skin damage. An example of a grading layout is shown in Figure 1.
Packaging
A range of package sizes and materials are available ranging from a several layer box to a single layer tray. The package and style used will depend on the market destination of the melons. Packaging and labels are important in presenting the fruit attractively but the most important function of the carton is to protect the melons. Melons destined for export should go in cartons suitable for the climatic conditions, and the handling requirements of the market. Unwaxed fibreboard cartons will not stand up to the damp humid conditions and handling requirements in South East Asia.
Fully waxed single layer trays are essential for the export market. The base of the carton should be above the height of the fruit. A full lid and dividers inside the box will protect the fruit, taking weight from above and adding rigidity and strength.
Storage after packing
The packed melons should then be cooled to the holding temperature as quickly as possible. Even if cooled prior to packing the internal temperature of the fruit will have risen significantly during grading. Prompt cooling to the holding temperature will maximise storage life.
Storage temperatures and times vary for different types of melons. Cantaloupes will store for 2-3 weeks at 2-4°C, Hami melon and green flesh melon for 2-4 weeks at 7°C, and Honeydew melon for 4 weeks at 7°C. New technologies can extend the storage life of some melon types. Rockmelons seem suited to the use of gas permeable wraps which can further extend the storage life at 2.5°C.
Summary
In summary, a number of different handling strategies can be used to take melons from the field to final storage.
Fruit can be cool-stored prior to packing if there is a backlog of fruit. Initial field heat must be removed and a fungicide dip applied. The whole process from field to storage should be achieved in less than 24 hours, and within 8 hours of harvest the fruit should be at a temperature not exceeding 15°C.
Ideally, melons should be in cool storage within 4 hours from harvest.
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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