Green coffee was subjected to thermal study of the reactions evolved during the roasting process. Specific heat, heats of reactions, pressure drop, and permeability of the packed coffee powder were obtained from the measurements. The sample was dried, therefore the thermograms showed no evidence of occluded water present in the coffee. The results showed predominant endothermic reaction in the range of 100 and 245° C mainly due to the formation of phenolic and nitrogen containing heterocyclic compounds. The reactions at temperatures above 245° C exhibited a double trough exotherm related to fracturing of the matrix and formation of cracks as a result of the decomposition of the lignin. The largest pressure build up and consequently lowest permeability was observed in this temperature range. The decomposition reactions were completed at 430° C.