Tempe bongkrek is one type of tempe from Central Java, or more popular from the Banyumas area, which is made from soybeans and coconut pulp. This tempeh often causes poisoning because it is contaminated by the bacteria Burkholderia galdioli which produces toxins in the form of bongkrekic acid and toxoflavin, and destroy the fungus Rhizopus due to the antibiotic effect of bongkrekic acid.
With frequent poisoning that can cause fatalities, the government bans the sale of this tempeh. But making it secretly continues to be done because it feels popular. Usually safe markers of bongkrek tempeh are a good smell, texture, and taste. Yellowish bongkrekic tempeh is usually a sign of the presence of toxoflavin. But bongkrek tempeh with a normal color still keeps the possibility of danger.
Source : wikipedia