The buah keluak (Pangium edule) tree is indigenous to Malaysia, Indonesia and Singapore, and is known as kepayang and kluwek in the first two countries respectively. The seeds of the buah keluak fruit are used in Malay, Indonesian and Peranakan cooking, after various processes of underground fermentation, soaking and cooking to leach the seeds of poisonous hydrocyanic acid.
Indonesian Black Nuts
Buah keluak belongs to the Achariaceae family of shrubs and trees, of which there are five species: two native and three cultivated, including buah keluak. These species were previously recorded under the Flacourtiaceae family, but are now listed under Achariaceae. This family consists of unisexual plants with alternate or spiral leaves, unisexual flowers with sepals and petals, and large fruits. The tree fruits at about 15 years of age and can live to a great age.
The buah keluak tree can grow up to 24 m in height, and the reddish-brown fruits are large and can range from 15 cm to 30 cm in length and 4.5 cm to 7.5 cm in width. Hydrogen cyanide, or hydrocyanic acid, is present in all parts of the tree, and young buah keluak seeds contain more of the poison than ripe seeds.
The species name edule means “edible” in Latin, while buah keluak means “the fruit which nauseates” in Malay and Indonesian. The fruit has also inspired a Malay proverb: laksana buah kepayang, dimakan mabuk, dibuang sayang (“like the fruit of the kepayang, which intoxicates you if you eat it and which you have not the heart to throw away; pretty by harmful”). The proverb is used in the context of something that is harmful but desirable.
Cultivated in villages in Indonesia and Malaysia, each buah keluak fruit can contain 20 to 30 triangular, grooved seeds about 5 cm in length, embedded in oily pulp. Seeds from wild buah keluak trees were traditionally harvested as well. In the wild, the seeds float in water for long periods and readily transported via water bodies like rivers and streams.
Preparation of buah keluak as food
Preparation of buah keluak as food
There are a number of methods traditionally used to leach buah keluak of its poison and prepare it as food. The fruit is usually left to ripen until the flesh falls away, after which the seeds are taken out. In one method, the seeds are crushed, boiled and put under running water for a day. After a second boiling, they are ready for consumption.
With the fermentation method, the boiled seeds are buried with ash in a pit. The seeds slowly ferment over a period of 40 days, changing their flavour and reducing the toxicity of the hydrocyanic acid. Much of the buah keluak imported into Singapore is prepared this way. Other methods involve variations in the soaking, boiling and fermentation periods. Consumption of improperly prepared or unripe seeds can cause vomiting, abdominal swelling, contraction of the tongue or even death.
In regional cooking, the buah keluak seeds are either cooked with their shells intact or with just the meat within and the shells discarded. In Singapore, the best-known buah keluak dishes are ayam buah keluak (in a chicken stew) and tulang babi buah keluak (in a pork rib stew). The buah keluak meat can also be mixed with prawns and pork and stuffed back into the shells to be cooked, or wrapped in banana leaves and steamed or grilled with spices. Ayam buah keluak has come to be seen as representative of Peranakan cuisine, as it combines a host of Southeast Asian spices and the long simmering process of Hokkien cooking.
The black, oily buah keluak has been described as an acquired taste, with flavours reminiscent of cacao (used in chocolate-making), mushrooms and black olives. It has been called the Asian equivalent of black truffles, as connoisseurs attest that buah keluak tastes like the highly prized fungus.
In Indonesia, the seed is used to flavour an east Javanese beef broth dish known as rawon. Less well known is trassi puchong, found in east Indonesia, where the buah keluak is mashed and boiled and mixed with lemongrass, chillies, shallots, salt and belacan (fermented prawn paste).
Buah keluak seeds can be pressed after a process of boiling, soaking and drying in the sun to obtain an oil that can be a substitute for coconut oil. Besides its use in cooking, the oil can be used in soap-making. Among those that use this oil are the Dayaks of Borneo. Cold-pressed oil is poisonous, and has been used by criminals to poison food, as well as used in European remedies for leprosy.
There are medicinal and preservative uses for buah keluak, as it is said to have anthelmintic (parasitic worm-destroying) qualities. In western Java, Indonesia, pounded seeds – with antiseptic properties – are placed inside the body and over fish as they are transported to the market, while freshly crushed seeds are applied to boils by the Malay community. In Pahang, Malaysia, crushed seeds are also used to lure fish and stupefy them.
Buah keluak leaves have a variety of uses. On the Indonesian island of Sulawesi, old leaves (young leaves contain more poison) are shredded, mixed with pig’s blood and salt, stuffed into bamboo and boiled for consumption. Fresh or pulped leaves, possessing anthelmintic qualities, are also applied to itchy skin caused by parasites and festering wounds. In eastern Malaysia, the leaves are at times used as a preservative wrap for meat or put into water to stupefy fish and shrimps.
Handling Keluak after Purchasing
Dried food stallholders who sell the buah keluak seeds (stripped of fruit) – in places like Tekka or Geylang Serai markets – say that the seeds are already extracted of poison by a variety of processes like soaking, boiling or burying in ash.
But to be on the safe side, once you have bought the seeds, the practice is to soak the nuts in large tubs of water for at least four to five days, changed twice a day, not only to extract any remaining poison but to get rid of the raw taste of mud.
It is also to soften the shells so that it is easily cracked and you can get better access to the delicious black nut that we all love.
The best substitute is unsweetened baking chocolate, with 100 percent cacao.