Oncom is a traditional Javanese fermented food made from okara (leftover from soymilk production) or peanut presscake (leftover from peanut oil production). In Indonesia, oncom is produced on the scale of a small cottage industry without using an oncom starter, resulting often in poor quality oncom. To improve the quality of oncom and to prevent the growth of toxic molds, it is important to use a commercial oncom starter. One of the strains used is Rhizopus oligosporus, a mold that is also used in tempeh production. Since oncom is made from by-products, it increases the economic efficiency of food production. Praised for its low cost, easy digestability and high nutritional value, oncom can be prepared and cooked in different ways.