Pretreatment is usually the first step in the processing of lignocellulosic biomass into biofuel-ethanol (sometimes known as "cellulosic ethanol"). This step is often used to liberate the cellulose/hemicellulose molecules from the tight "lignin wrapping" in the biomass and also to breakdown the liberated cellulose/hemicellulose molecules into simple sugars. The simple sugars are eventually fermented to ethanol by bacteria or yeasts. Although the application of dilute acid or dilute alkali have been the known technologies for lignocellulosic biomass pretreatment, some recent (and supposedly more efficient) technologies have been reported. Among these recent technologies are "steam explosion" and "ammonia fiber explosion (AFEX)" pretreatments. Both processes involve the application of heat to the biomass under pressure (together with either steam or ammonia), then suddenly releasing the pressure. The sudden release of pressure explosively ruptures the biomass fibers and eventually breaks down the cellulose/hemicellulose molecules into simple sugars (glucose/xylose). Scientists from the Michigan State University (United States) recently compared the performance of AFEX and dilute acid treatment with respect to the amount of sugars liberated and the fermentability of the resulting hydrolyzates to ethanol. They found that AFEX pretreatment resulted in better fermentability but required supplemental addition of enzymes (xylanase and cellulase). Dilute acid treatment on the other hand, would not require enzyme supplementation, but had lesser fermentability. Details of the study are published in the open-access journal, Biotechnology for Biofuels (URL above)..