This work presents the results of analysis of organic coffee beans grown in the department of Cauca – Colombia. The beans studied are of the species Coffea arabica grown in mountain soils, at a medium altitud of 1500 meters above sea level. Thermogravimetry (TGA) and Fourier Transform Infrared Spectroscopy were used to characterize the coffee powders obtained by grounding green coffee beans, as well as roasted beans at a temperature ranging from 210 to 230 0 C. The main purpose of this investigation is to determine the transformations produced by roasting and to associate the changes to patterns of identification of functional groups by FTIR spectroscopy. Infrared absorption peaks evidencing the main changes produced by roasting are present at 880 cm -1 , by anomeric bands of carbohydrates, at 1160, 1250, and 1380 cm -1 due to action of the chlorogenic acid, and in the region of 1500 to 1800 cm -1 with a outstanding peak at 1650 cm -1 due to the presence of caffeine. The TGA spectra show that the transformation of the coffee is accelerated starting at 200 0 C, and it exhibits a singular point at 218 0 C, this point is the critical temperature value to obtain excellent quality coffee.