Tempeh Bongkrek or the hunt for the forbidden ferment

Not the real tempeh- but irresistible nevertheless, because of it’s status of being prohibited. The forbidden fruit in de garden of FermentEden. Though this fruit might be forbidden for a good reason.

Tempeh bongkrek, a weird and dangerous delight, made of fermented coconut press cake, is only produced in Java, Indonesia. The coconut press cake, a byproduct of coconut milk and oil production is left to ferment after inoculation with the same mold fungus used for classical tempeh, Rhizopus Oligosporus, often by reusing banana leaves from tempeh production.

Consumption of tempeh bongkrek has led to hundreds of lethal poisonings, which lead to it’s prohibition by the Indonesian government in 1988. Researchers found that all the poisonous samples were contaminated with a certain bacteria (Burkholderia gladioli pathovar cocovenenans) that produces one of the strongest respirational toxins known (bongkrekic acid), able to kill within 4 hours after consumption.[1]

Mostly this, and other bacteria are outnumbered by the fast growing rhizopus oligosporus. A pH lower than 6 inhibits bacterial growth and the production of bongkrekic acid. Therefore tempeh, when made the right way with proper acidification (by a first fermentation as is done in Indonesia, or by adding vinegar as is done in the western world) is a safe food. Unfavourable conditions like a temperature too high or too low, acidity too low (pH>6) or too much moisture, stimulate the growth of bacteria, which in this case originates from the badly handled coconut press cake. The reason why only tempeh bongkrek contains the poisonous bongrekic acid, is because the bacteria is found to produce the toxin where there is a high content of specific types of fatty acids, found in coconut. Soybean tempeh, even when the bacteria is present, doesn’t contain the toxin. A traditional way of avoiding bongkrekic acid is by adding shredded oxalis sepium leaf to acidify the coconut pulp. This results in a green tempeh, which looks weird and and is not very popular.

Luckily there is a safety check for tempeh bongkrek: along with the colourless bongkrekic acid, another, yellow toxin is produced, visible on the inside of the cake when cracked open. So yes- even in snowless Indonesia, we hear Frank Zappa’s warning.

This said- if the coconut press cake is handled well, the result should be a beautifully fermented delicacy. Favourable conditions are inoculation of the coconut pulp within 18 hours after production, hygienic and cool handling and transportation, adding 2% salt to the pulp and well pressed coconut shreds to lower the fat residue.

I ‘ve been hearing rumours of tempeh bongkrek still being produced on Java. Traditions are not easy to change, the more since it’s a cheap, tasty and efficient way of processing coconut waste.  Tempeh bongkrek “lives” on, underground, and i won’t rest before i find it.

Sources, beside the rumours:

Garcia et al. (1999), “The effect of lipids on bongkrekic (Bongkrek) acid toxin production by Burkholderia cocovenenans in coconut media” in Food Additives and Contaminants, 1999, Vol. 16, No. 2, pages 63- 69

Moebius N. (2012). “Biosynthesis of the Respiratory Toxin Bongkrekic Acid in the Pathogenic Bacterium Burkholderia gladioli” in Chemistry and Biology Volume 19, Issue 9, 21 September 2012, Pages 1164-1174

Shurtleff W. & Aoyagi A. (1997), the book of tempeh, Soyinfo Center

[1] To understand how the poison works, this fantastic blogger tries to explain in layman’s terms.