Melons

Infobox on Melons
Example of Melons
Freshness facts
Optimum carrying temperature	2°C to 4°C (Cantaloupe) 8°C (Galia, Orange flesh) 10°C (Honey Dew, Piel de Sapo, Watermelons)
Highest freezing point	-1°C
Acceptable product temp. at loading into containers	Max. 2°C above carrying temperature
Optimum humidity	90%-95%
Ventilation setting for containers	25 m³/hr
Storage life	2-4 weeks (variety dependent)
Climacteric / non-climacteric	Climacteric (Muskmelons) Non-climacteric (Watermelons)
Ethylene production	Moderate
Ethylene sensitivity	High
Modified / controlled atmosphere	10%-20% CO2; 3%-5% O2
Potential benefits	Slight to moderate
Availability
South Africa South America Central America	December - May September - April December - May

Melons

Harvesting and handling

Cantaloupes

Cantaloupes are harvested by maturity and not by size. Commercial maturity is ideally at the firm-ripe stage or "3/4 to full-slip" when a clear abscission (slip, separation) from the vine occurs with light pressure. Cantaloupes ripen after harvest but do not increase in sugar content.

Cultivars vary in their external colour at this stage of maturity and may retain a greenish cast. This skin colour typically transitions from grey to dull green when immature, deep uniform green at maturity, and light yellow at full ripeness. A raised and well-rounded netting on the fruit surface is another indicator of proper commercial maturity.

High relative humidity is essential to maximise postharvest quality and prevent desiccation. Water loss through scuffed and damaged surface netting can be significant. Extended periods of higher humidity or condensation may encourage the growth of stem-scar and surface moulds.

Packaging in twist-tied closed and secured mouth-ends of polythene bags will create a Modified Atmosphere (MA) inside the bags. A combination of proper (pre-)cooling and increased CO₂ percentage should inhibit mould growth. A sub-optimum condition of the commodity at the shipping point and/or improper (pre-)cooling of same may have an adverse effect on the MA conditions².

Storing cantaloupes below 2°C will result in chilling injury, which is characterized by pitting, off-flavours and increased surface decay.

Galia, Orange flesh, Honeydew, Piel de Sapo Melons are climacteric, but as they have no starch reserves they cannot become significantly sweeter after harvest. Therefore melons are usually harvested at the hard-ripe stage. However, maturity is difficult to judge because no clear abscission (slip, separation) from the vine occurs. Postharvest ripening is restricted to softening of the flesh and development of flavour volatiles. Prompt pre-cooling of melons is highly desirable since it retards the breakdown of sugars.

A non-optimal condition of the commodity at the shipping point and/or improper cooling of same during (part of) the storage/transit period may have an adverse effect on the PSL (Potential Storage Life) and condition of the fruit. It is said that four days delay in the pre-cooling of certain melon varieties might reduce the shelf life with a week.

Storing at temperatures <5°C will induce chilling injury in these melons.

Watermelons

Quality in watermelons is determined largely by high sugar content, a deep red flesh colour and a pleasant crisp texture of the edible flesh. These factors are dependent on maturity, cultivar and handling methods. Commercial melons for distant markets are usually harvested when mature, but before full ripeness, to minimise handling damage and flesh breakdown. They are at their best for eating when mature but pre-climacteric. Immature melons have a pink flesh, mature melons are red to dark red, and over-mature ones have orange flesh. Actually, the red colour and flavour of watermelons improve during storage for 7 days at or above room temperature, while at 10°C or below colour fades. After watermelons reach optimum harvest maturity, soluble solids content (brix) does not increase during storage.

Relative humidity is not critical, since watermelons do not readily lose moisture. They are sensitive to ethylene, however.

Watermelons are not adapted to long storage. At low temperatures (<7°C) they are subject to various symptoms of chilling injury and loss of quality, and at high temperatures they are subject to decay. Around 10°C is a good compromise. Watermelons should keep at this temperature range for 2 or 3 weeks; some will keep longer. Melons held 6 weeks at room temperature will have poor flavour.

Although decay is usually not a major form of deterioration, extended storage at warm temperature will result in more decay than at cooler temperatures.

Rough handling will result in serious losses. Watermelons should not be dropped, thrown, or walked on, as internal bruising and flesh breakdown will occur.

Cooling and storage

All the cucurbits have tropical ancestors, and suffer physiological disruption at low temperatures. Chilling injury can result from low temperatures in the field, but is more usually a consequence of inappropriate storage or transit conditions. The time factor is critical, and a brief exposure (2 or 3 days) may cause no harm. The longer the period of exposure and the lower the temperature, the greater the damage sustained. Symptoms (which vary with the conditions imposed) may not develop until the produce is returned to a higher temperature, when rapid deterioration ensues.

When melons are stored too long or at too low a temperature, they deteriorate (decay, surface breakdowns, softening or off-flavours) so rapidly upon transfer to room temperature, that they soon become worthless.

Evidently elevated storage temperatures will not only be disadvantageous to the condition of the melons, but also enhance any decaying process to which the produce may be predisposed. Several species of bacteria may be present in the internal tissues of healthy fruit. Under certain circumstances, these bacteria can multiply and cause serious disease.

Warm, wet melons are subject to invasion by micro organisms.

Mixed loads

Do not ship with ethylene-producing commodities.

Cautions

CO₂ above 10% produces a carbonated taste that is lost during subsequent air storage.

Storage disorders

Alternaria rot, Anthracnose, Bacterial rots, Blossom end rot, Blue mould, Botryodiplodia rot, Chilling injury, Cladosporium rot, Cotton end rot, Cottony leak, Fusarium, Grey mould rot, Myrothecium rot, Pink mould rot, Pythium rot, Rhizoctonia rot, Rhizopus rot, Sclerotium rot, Senescent breakdown, Sour rot, Watery soft rot.

²Modified Atmosphere (MA); an atmosphere in which oxygen, carbon dioxide and nitrogen concentrations are different from those in air, but are not precisely regulated.