composed of sugars and is subject to both alcoholic and lactic fermentation. Sucrose is also hydrolysed to reducing sugars. Lactic acid is not usually metabolized further during cocoa fermentation, but ethanol is oxidized to acetic acid by acetic acid bacteria. Excessive acidity is a fault in cocoa beans. Production of acetic acid in the early stages of fermentation restricts the final quantity formed due to inhibition of yeasts and limitation of the quantity of ethanol available as a substrate. Acetic acid is itself oxidized, either by acetic acid bacteria or other microorganisms and the concentration tends to fall towards the end of fermentation, especially if the beans are highly aerated. A substantial proportion of acetic acid is lost during drying and roasting , but lactic acid is less volatile and tends to be responsible for acidity in cocoa powder.