Researchers from the Michigan State University (United States) investigated the use of the Ammonia Fiber Expansion (AFEX) process for the pretreatment of switchgrass (Panicum virgatum), at different harvest times and different ecotypes/locations. The AFEX process involves the addition of liquid ammonia into the biomass, at pressures between 100 psi to 400 psi (pounds per square inch) and temperatures between 70 to 200 degrees Celsius. A reactor which is (in many ways) similar to a pressure cooker is used. The pressure is held for some time and then rapidly released. The sudden release in pressure explosively disrupts the lignocellulose fibers, resulting in the breakage of the biomass lignin-carbohydrate matrix, and the release of sugars. Results showed that "each harvest type and location responded differently to AFEX treatment". The least mature sample required the least severe pretreatment conditions (i.e., temperature, pressure, loadings) and had the highest sugar release. The most mature harvest had the least amount of sugar released. Details of the study are published in the open access journal, Biotechnology for Biofuels (URL above)..