Torrefaction has been shown to be a viable pre-treatment process for thermally upgrading biomass and making it better suited for use as a fuel. Results are presented here from the torrefaction of two different woody biomass (Mesquite and Juniper) using thermogravimetric analysis (TGA). Samples were torrefied in two different mediums (Nitrogen and Carbon-dioxide) to investigate the impact of inert and non-inert gases on the thermal degradation of the biomass, specifically mass loss as well as the breakdown of hemicellulose, cellulose, and lignin. A wide range of torrefaction temperatures ranging from 200 to 300 degrees C was investigated at a single residence time. TGA thermograms showed increased amounts of weight loss when the biomass was torrefied in a Carbon-dioxide environment compared to inert environments, while derivative thermogravimetric analysis (DTA) showed a drop in the peak rate of hemicellulose and cellulose weight loss when using Carbon-dioxide as the torrefaction medium. Fuel properties analysis of samples subjected to a mild torrefaction process (240 degrees C) showed increases in ash and fixed carbon content of the biomass, independent of torrefaction medium. Furthermore, comparison of the grindability of raw and torrefied samples showed torrefaction in a Carbon-dioxide environment further improved the grindability of the torrefied biomass. The effect of inert and non-inert torrefaction mediums on the volatile species (CO2, CO, CH4, and C2H6) released from torrefied Mesquite during pyrolysis was further investigated via TGA-FTIR analysis. (C) 2013 Elsevier Ltd. All rights reserved.