Fermentation in cocoa beans begins with the growth of micro-organisms, Yeast grows on the pulp surrounding the beans. Insects, like the vinegar fly, might be responsible for bringing micro-organisms to the beans. The yeast turns the sugar in the pulp to ethanol. Bacteria then starts to oxidize the ethanol; into acetic acid, and then into carbon dioxide and water. These chains of events ends up producing more heat and raises temperature for the beans. The length of fermentation varies depending on the bean type.