Oncom is one of the traditional staple food

Staple food

A staple food is one that is eaten regularly and in such quantities that it constitutes a dominant portion of a diet, and that supplies a high proportion of energy and nutrient needs. Most people live on a diet based on one or more staples...

s of West Java

West Java

West Java , with a population of over 43 million, is the most populous and most densely populated province of Indonesia. Located on the island of Java, it is slightly smaller in area than densely populated Taiwan, but with nearly double the population...

n (Sundanese

Sundanese people

The Sundanese are an ethnic group native to the western part of the Indonesian island of Java. They number approximately 31 million, and are the second most populous of all the nation's ethncities. The Sundanese are predominantly Muslim...

) cuisine

Sundanese cuisine

Sundanese cuisine is the cuisine of Sundanese people of West Java, Indonesia. It is among one of the most popular food in Indonesia. The Sundanese food is characterize with its freshness; the famous lalab eaten with sambal and also karedok demonstrate the Sundanese fondness for fresh raw vegetables...

. There are two kinds of oncom: red oncom and black oncom. Oncom is closely related to tempeh

Tempeh

Tempeh , or tempe , is a traditional soy product originally from Indonesia. It is made by a natural culturing and controlled fermentation process that binds soybeans into a cake form, similar to a very firm vegetarian burger patty...

; both are foods fermented

Fermentation (food)

Fermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. Fermentation in simple terms is the chemical conversion of sugars into ethanol...

 using mold

Mold

Molds are fungi that grow in the form of multicellular filaments called hyphae. Molds are not considered to be microbes but microscopic fungi that grow as single cells called yeasts...

.

Usually oncom is made from the by-product

By-product

A by-product is a secondary product derived from a manufacturing process or chemical reaction. It is not the primary product or service being produced.A by-product can be useful and marketable or it can be considered waste....

s from the production of other foods -- soy bean tailings (okara) left from making tofu

Tofu

is a food made by coagulating soy milk and then pressing the resulting curds into soft white blocks. It is part of East Asian and Southeast Asian cuisine such as Chinese, Japanese, Korean, Indonesian, Vietnamese, and others. There are many different varieties of tofu, including fresh tofu and tofu...

, peanut

Peanut

The peanut, or groundnut , is a species in the legume or "bean" family , so it is not a nut. The peanut was probably first cultivated in the valleys of Peru. It is an annual herbaceous plant growing tall...

 presscake left after the oil

Oil

An oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils....

 has been pressed out, cassava

Cassava

Cassava , also called yuca or manioc, a woody shrub of the Euphorbiaceae native to South America, is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy tuberous root, a major source of carbohydrates...

 tailings when extracting the starch

Starch

Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...

 (pati singkong

Tapioca

Tapioca is a starch extracted Manihot esculenta. This species, native to the Amazon, Brazil, Colombia, Venezuela, Cuba, Puerto Rico, Haiti, the Dominican Republic, Honduras, and most of the West Indies, is now cultivated worldwide and has many names, including cassava, manioc, aipim,...

), coconut

Coconut

The coconut palm, Cocos nucifera, is a member of the family Arecaceae . It is the only accepted species in the genus Cocos. The term coconut can refer to the entire coconut palm, the seed, or the fruit, which is not a botanical nut. The spelling cocoanut is an old-fashioned form of the word...

 presscake remaining after oil has been pressed out or when coconut milk

Coconut milk

Coconut milk is the water that comes from the grated meat of a coconut. The colour and rich taste of the milk can be attributed to the high oil content. In many parts of the world, the term coconut milk is also used to refer to coconut water, the naturally occurring liquid found inside the hollow...

 has been produced.

Since oncom production uses by-product

By-product

A by-product is a secondary product derived from a manufacturing process or chemical reaction. It is not the primary product or service being produced.A by-product can be useful and marketable or it can be considered waste....

s to make food, it increases the economic efficiency of food production.

Red oncom reduces the cholesterol levels of rats, suggesting effects in humans.

Black oncom is made by using Rhizopus oligosporus

Rhizopus oligosporus

Rhizopus oligosporus is a fungus of the family Mucoraceae that is a widely used starter culture for the home production of tempeh. The spores produce fluffy, white mycelia, binding the beans together to create an edible “cake” of partly fermented soybeans.Rhizopus oligosporus produces an...

while red oncom is made by using Neurospora intermedia var. oncomensis. It is the only human food produced from Neurospora

Neurospora

Neurospora is a genus of Ascomycete fungi. The genus name, meaning "nerve spore" refers to the characteristic striations on the spores that resemble axons....

.

Toxicity

In the production of oncom, sanitation and hygiene are important to avoid contaminating the culture with bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 or other fungi like Aspergillus flavus

Aspergillus flavus

Aspergillus flavus is a fungus. It is a common mold in the environment, and can cause storage problems in stored grains. It can also be a human pathogen, associated with aspergillosis of the lungs and sometimes causing corneal, otomycotic, and nasoorbital infections. Many strains produce...

(which produces aflatoxin

Aflatoxin

Aflatoxins are naturally occurring mycotoxins that are produced by many species of Aspergillus, a fungus, the most notable ones being Aspergillus flavus and Aspergillus parasiticus. Aflatoxins are toxic and among the most carcinogenic substances known...

). Neurospora intermedia var. oncomensis and Rhizopus oligosporus

Rhizopus oligosporus

Rhizopus oligosporus is a fungus of the family Mucoraceae that is a widely used starter culture for the home production of tempeh. The spores produce fluffy, white mycelia, binding the beans together to create an edible “cake” of partly fermented soybeans.Rhizopus oligosporus produces an...

reduce the aflatoxin produced by Aspergillus flavus

Aspergillus flavus

Aspergillus flavus is a fungus. It is a common mold in the environment, and can cause storage problems in stored grains. It can also be a human pathogen, associated with aspergillosis of the lungs and sometimes causing corneal, otomycotic, and nasoorbital infections. Many strains produce...

. However, aflatoxin-producing molds (Aspergillus spp.) are often naturally present on peanut presscake. Furthermore coconut presscake can harbor the very dangerous Pseudomonas cocovenenans, which produces two highly toxic compounds - bongkrek acid

Bongkrek acid

Bongkrek acid is a respiratory toxin more deadly than other mitochondrial poisons cyanide or 2,4-dinitrophenol. There was some dispute regarding the actual structure of bongkrek acid but this was resolved in 1973, which explains different structures appearing in the literature prior to this...

 and toxoflavin

Toxoflavin

Toxoflavin is a toxin produced by a variety of bacteria including Burkholderia gladioli. It also has antibiotic properties.Toxoflavin acts as a pH indicator, changing between yellow and colorless at pH 10.5....

. Shurtleff and Aoyagi address toxicity in their book section on oncom.

While it is known that soybean

Soybean

The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...

s are the best substrate for growing R. oligosporus to produce tempeh

Tempeh

Tempeh , or tempe , is a traditional soy product originally from Indonesia. It is made by a natural culturing and controlled fermentation process that binds soybeans into a cake form, similar to a very firm vegetarian burger patty...

, oncom has not been as thoroughly studied; the best fermentation substrates for producing oncom are not yet known.