Durian should be allowed to fall to the ground so that it is really sweet and mature. The fruit in its own and fermented fruit will reduce the quality in terms of durian content and taste of durian.
Fruit is graded on weight, shape, size, and defects. Defects include disease, insects, mechanical injury, and flesh disorders. Since the fruit is packed into Cardboard cartons (4 to 6 fruit per carton), it is important to ensure that there is no direct fruit of the disease or insect as this will cause all the fruit in the cartons to infect and make the fruit is broken and less quality.
The pulp of half- to near-full ripe fruit is much less sensitive to chilling injury than the peel, and the pulp can be stored for 4 weeks at 5°C (41°F). Whole fruit stored at less than 15°C (59°F) develops chilling injury consisting of the peel turning black or dark brown, starting at the groove between the splines and will affect durians quality. Chill-injured pulp suffers a loss of aroma, does not soften, and may develop sunken areas on the surface.
Durian is odoriferous, and all the more so when fully ripe. However, the outside of a perfectly ripe durian doesn’t have the same sharp pungency as the inside. Since the shell of the durian doesn’t contain the same volatiles as the flesh, if the durian hasn’t been broken open yet, either by force of falling or a knife, the odor should remain mostly sealed inside. This varies slightly with the thickness of the shell. If the durian has no smell at all, chances are it’s not ripe. If it smells really strong, chances are it’s overripe. When the fruit is brought close to the nose, one should experience a low level, earthy yet sulfurous smell, like fresh-cut grass and scrambled eggs.
When ripe, durians fall off the tree. That’s why durian orchards have such a bad rap – every year, several people are injured or die from falling durians. If the durian fell within the last day, chances are that it’s perfect. Allowing a durian to sit for up to 12 hours improves the flavor (and drug-like effects), but it’s up to personal tastes. Ask the vendor if the durian fell, and how long ago. If the person selling the durians also owns the trees, chances are the person knows exactly what time of day or night that particular durian fell, and from which tree - or exactly how long that particular durian has been sitting around at the stall. Knowing if the durian fell is a good start, but immature durians sometimes get knocked down due to strong winds, rain, animals, or a natural culling process when the tree has too many fruits. In many countries, durians are purposefully cut off the three days before it would have fallen, for transportation or ease of harvest.
When a durian falls from the tree, it breaks off at a weakened groove on the stem. The botanical term is “abscission layer”. The stem of a ripe durian, no matter whether it fell or was cut early, should break off at that point. One can test how close to ripe a cut durian is by wiggling the stem – if it’s loose at that point, the durian is close to ripe. If it has broken off already or comes off easily in the hand, the durian is ripe. Mind, the stem should still be fully attached and fresh-looking, with a green hue coming through the brown skin. When the stem is scraped with the thumbnail, the interior should be grass green. If the stem is shriveled, or dark brown, the durian is days old, and chances are it was cut early and has been ripening under a tarp. It may be ripe and taste okay, but the flavor is always better from durian that falls on its own.
One of the easiest ways to tell if a durian is ripe is to hold it to the ear and shake it. The flesh of a ripened durian is soft, which allows the seeds to bang around inside the shell-like a maraca filled with gak. If the seed is rattling around with no resistance, chances are the durian is overripe. If there is nothing that can be heard or felt, the durian flesh is hard.
If the durian sounds slightly hollow, it means the flesh has softened enough to recede from the shell, and the durian is at least edible. Various levels of hollowness correlate to levels of softness.