Looking like a cross between a pineapple and a cantaloupe, with a prickly outer skin that demands careful handling, the durian is highly prized as a delicacy in its native Brunei, Indonesia, and Malaysia. There are thirty recognised species of the genus Durio and the tall evergreen trees regularly top one hundred feet. Fruiting once or twice a year, they take three months after pollination to produce a ripe fruit. It is easy to see why as the fruit is no shrinking violet, weighing up between two and seven pounds and measuring a foot in width, with brown or green husks and pale yellow or red flesh, depending upon the particular species.
Proponents of the durian point out that it is packed with antioxidants and rich in potassium, iron and vitamins B and C, making it ideal for lowering blood pressure, improving skin texture and muscle strength. Containing 23 grams of dietary fibre, a single fruit is sufficient to meet our daily nutritional requirements. Superfruit it may be, but the durian stands out in another respect, the aroma that accompanies it.
Smell is one of the most subjective of senses, curiously there is no commonly accepted metric for describing or rating smells, and the durian is the Marmite of fruits. Some think that it has a pleasantly sweet fragrance while others, the majority, certainly amongst Occidentals, think that it has an overpowering and deeply unpleasant odour that lingers for days. What is known in the Far East as the “king of the fruits” has earned itself the sobriquet of the world’s smelliest fruit. So offensive is the smell to many that it is banned on buses, trains, planes and many public spaces across Singapore, Thailand, Japan, and Hong Kong. Taxi drivers will refuse you entry into their cab if you are carrying one and hotels display signs advising their clientele “No Durian Allowed”. It is, nonetheless, the official Singaporean fruit and has left its mark on the city’s skyscape, the Esplanada building, adjacent to the city’s Marina Bay, resembling a durian cut in half.
Aside from taste and smell, the durian falls foul of those who, in these more environmentally aware times, are concerned with food waste. Around 70% of the fruit is discarded because it is inedible. This shockingly high level of waste led a team of chemical engineers from the University of Sydney, headed by Vincent Gomes, to consider whether the inedible parts could be deployed in another way.
Their principal objective was to find an alternative source to power mobile devices, given that the lithium-ion battery, so favoured by manufacturers, loses its ability to hold a charge over time, is inefficient in extreme weather conditions and the mining activities associated with its production come with a high social and environmental cost. Could the inedible parts of the durian, together with that of another Asiatic favourite, the jackfruit, be turned into a super-capacitor, a type of reservoir that charged and discharged energy?
By heating, freeze-drying, and baking the inedible, spongey core of the fruits in an oven at a temperature of more than 1500C, they produced a black, highly porous, ultra-light structure which they moulded into electrodes for a low-cost super-capacitator. The resulting super-capacitor could be charged up in just thirty seconds and was able to power up a range of electronic devices, including mobile phones, tablets, and laptops, in just a few minutes. Gomes and his team may just have found a new and sustainable way to store energy for domestic use.
If it does come to fruition, it is no thanks to Gomes’ wife. Having taken the risky step of using his home freezer to store the fruit, perhaps he should not have been too surprised when she, finding the stench emanating from them too offensive, cleared them out. Being married to an inventor is no bowl of cherries, it would seem.