|Place of origin||Maritime Southeast Asia|
|Region or state||Southeast Asia|
|Associated national cuisine||Indonesia|
Oncom (Indonesian pronunciation: [ɔnˈtʃɔm]) is one of the traditional staple foods of West Javan (Sundanese) cuisine of Indonesia. There are two kinds of oncom: red oncom and black oncom. Oncom is closely related to tempeh; both are foods fermented using mold.
Usually oncom is made from the by-products from the production of other foods: soy pulp left from making tofu, peanut press cake left after the oil has been pressed out, cassava tailings when extracting the starch (pati singkong), coconut press cake remaining after oil has been pressed out or when coconut milk has been produced. Since oncom production uses by-products to make food, it increases the economic efficiency of food production.
In the production of oncom, sanitation and hygiene are important to avoid contaminating the culture with bacteria or other fungi like Aspergillus flavus (which produces aflatoxin). Neurospora intermedia var. oncomensis and Rhizopus oligosporus reduce the aflatoxin produced by Aspergillus flavus. However, aflatoxin-producing molds (Aspergillus spp.) are often naturally present on peanut presscake. 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.
- Sastraatmadja, D. D.; et al. (2002). "Production of High-Quality Oncom, a Traditional Indonesian Fermented Food, by the Inoculation with Selected Mold Strains in the Form of Pure Culture and Solid Inoculum". J. Grad. Sch. Agr. Hokkaido Univ. 70: 111–127. hdl:2115/13163.
- "Plasma cholesterol reduction by defatted soy ontjom (fermented with Neurospora intermedia) in rats fed a cholesterol-free diet". usda.gov. Retrieved 25 March 2019.
- Ho, C.C. (1986). "Identity and characteristics of Neurospora intermedia responsible for oncom fermentation in Indonesia". Food Microbiology. 3 (2): 115–132. doi:10.1016/S0740-0020(86)80035-1.
- "Effect of Rhizopus and Neurospora spp. on growth of Aspergillus flavus and A. parasitus and accumulation of aflatoxin B1 in groundnut". inist.fr. Retrieved 25 March 2019.
Also, There is an appendix on oncom in Aoyagi and Shurtleff's _Book of Tempeh; Professional Edition_, online at Google books.