Traditionally, ripe fruits are allowed to drop on to the ground naturally and later collected for the market. Malaysian durian growers do not pluck fruit at the mature stage as what is widely practiced in Thailand. Although naturally dropped fruit has a better eating quality, it has very short storage life (3-4 days), which hinders the fruit from being transported to distant markets.

Harvesting the fruit from the tree at maturity has an advantage in that the fruit takes a longer time to ripen and can be transported to distant markets. Fruit maturity plays a very important role in ensuring that the harvested fruit has a good eating quality and is acceptable by consumers. Fruits that are harvested earlier than the optimum stage of maturity will have a poor eating quality. In contrast, fruits that are harvested too late have a shorter storage life, as the fruits may have ripened on the tree. Durian, therefore, should be harvested at an optimum stage of maturity for optimum quality and storage life.

Reliable maturity indices are very important to determine the best time for harvesting. Criteria such as age of fruit based on calendar date, the appearance of the fruit stalk and the fruit surface, the sound of fruit from tapping, and the smell of the fruit are commonly related to fruit maturity in durian. However, not all the criteria can be applied for all durian cultivars as one single criterion or several criteria may be suitable for some cultivars but not for some other cultivars.

Calender date

The time taken from flowering, flower anthesis or fruit-set to maturity is always used as a guide for harvesting. Generally, durian fruits mature 3-5 months after flowering – depending on the cultivar . For example, the fruit of early maturing cultivars will mature 90-100 days after anthesis while a medium maturing cultivar will mature 100-120 days after anthesis . The late maturing cultivars will mature 120-130 days and the fruit of very late maturing cultivars will take 140-150 days to mature. Table 1 indicates the age of fruit suitable for harvesting recommended for certain durian cultivars grown in Malaysia and Thailand.

Table 1: Days from anthesis (full bloom) recommended as maturity indices for selected durian cultivars

However, calendar date is not always a reliable harvesting index though it can be used as a general guide. The number of days from anthesis may vary with growing area, temperature and rainfall patterns. Furthermore, flower emergence and anthesis on the same tree do not occur at the same time. Normally, a tree will take about 2 weeks to complete flowering in a particular season. The suitable time of harvesting can be estimated from the date at which about 70% of flowers are at full bloom or anthesis .

Bulging abscission zone and abscission layer

The abscission zone in the fruit stalk swells as the fruit matures. This is more pronounced in the Chanee cultivars (Thai varieties). The Malaysian clone, D24, the mature fruit exhibits the swelling abscission zone together with the formation of the abscission layer. However, the swelling in D24 is not as pronounced as in Thai cultivars. The development of an abscission layer on fruit stalk can be a good harvesting index for D24 cultivar . The fruit can be harvested when the abscission layer has developed evenly around the fruit stalk. The fully developed abscission layer around the stalk indicates the maturity of the fruit is at an advanced stage and the fruit is about to ripen.

Spines
The immature fruit is green or light brown in colour. For many cultivars, the tips of spines turn dark brown when the fruit matures. This is in contrast to the lighter colour of the spine base. However, skin colour may influenced by light intensity. In addition, mature fruits have elastic, flexible spine tips that can be pulled together by the fingers more easily than those of immature fruit.

Carpel sutures
The carpel sutures become more pronounced as the fruit matures. The formation of sutures between locules is the most reliable maturity index for D24 cultivar . The sutures normally develop on the fruit about 100 days after flower anthesis . The suture of mature fruit can be seen very clearly even for fruit located at higher branches. The appearance of suture lines is more pronounced on overly mature fruit.

Sound from tapping
Mature fruits sound hollow when a finger tip, knife or wooden stick is run through or knocked on fruit spines. The fruit sounds solid if it is not fully mature. The relationship between sound and maturity may be due to the development of free space between the pulp and the wall of fruit husk during maturation. However, workers who harvest fruits must be well-trained and have enough experience to detecting fruit maturity with this method.

Smell
Fruits that are very close to ripening or are already ripe produce a characteristic odour. Fruits harvested at this stage are not suitable for distant markets or long storage.

Tree-ripened fruit needs to be rapidly transported to the market and consumed within 2 to 3 days after harvesting. Delayed handling is unacceptable as the fruit rapidly begins to split and ferment beyond this period. Fruits that either drop naturally or are hand-harvested are collected and transported to the collection centre or directly to the packinghouse. The fruits are usually placed in bamboo or plastic baskets. For small orchards, fruits are normally carried either manually or by bicycles or on motorcycles. In bigger orchards or plantations, lorries or tractor-mounted trailers are common modes of in-field transport. Farm roads should be kept in good condition. Great damage can be inflicted on durian fruit carried over rough roads as the fruit inside the containers can rub on one another resulting in broken spines. Damaged fruits are prone to infection by pathogen .

Packinghouse operations
The packinghouse is a place where the preparation of the produce for market is carried out. It can be built in the farm itself or in other close-by areas that have better infrastructure. A packinghouse can be a simple shed that is similar to an in-field collection centre or a complex equipped with all necessary sophisticated facilities. A practical packinghouse should have a good supply of clean water, electricity, a working area and storage space. In a packinghouse, the fruits undergo a series of operations before they are distributed to the market ( Fig. 1 ).

Fig.1. A flow chart of postharvest handling of durian

Durian fruits must be transported quickly to the market because the fruits dehisce and spoil easily during transportation. Fruits that drop naturally must be marketed and consumed within 2-3 days. Durian fruits are normally transported by lorries or vans. Bamboo baskets packed with durian fruits are arranged in the lorries either, in a single or double layers. Wooden crates or corrugated fibreboard cartons packed with fruits may be arranged in more than two layers depending on the size of the vehicles used. During transportation, the lorries are covered with canvas so that the fruits are not exposed to direct sunlight. Transportation should be done at a cooler time of the day and preferably at night.