After natural / wet processing of coffee cherries, de-hulled coffee beans are roasted to give typical flavor and aroma. Roasting is a time temperature dependent process where chemical and physical changes takes place in the green coffee. During roasting, there is also loss of dry matter, primarily as CO2 gas and other volatile products of the pyrolysis. About half of total CO2 generated are retained in the roasted coffee together with a major proportion of the important volatile flavor substances. Roasting is normally carried out under atmospheric pressure with hot air and combustion gases as the primary heating agent. Though heat may also be provided by contact with hot metal surface.