 Furthermore, coconut presscake can harbor the very dangerous "Burkholderia gladioli", which produces two highly toxic compounds – bongkrek acid and toxoflavin.Shurtleff and Aoyagi address toxicity in their book section on oncom.While it is known that soybeans are the best substrate for growing "R. oligosporus" to produce tempeh, oncom has not been as thoroughly studied; the best fermentation substrates for producing oncom are not yet known.