Cellulose is the single most important component of plant biomass. Like starch, it is made of linked sugar components that may be easily fermented when separated from the cellulose polymer. The complex structure of cellulose makes separation difficult, but enzymatic means are being developed to do so. Perfection of this technology will create a large potential for ethanol production using plant materials that are not human foods. The efficiency with which biomass may be converted to ethanol or other convenient liquid or gaseous fuels is a major concern.
Conversion generally requires appreciable energy.
If an excessive amount of expensive fuel is used in the process, costs may be prohibitive. Inputs for the corn system include energy for production and application of fertilizer and pesticide, tractor fuel, on-farm electricity, etc., as well as those more directly related to fermentation. A recent estimate puts the industry average for energy output at 133 percent of that needed for production and processing. This net energy gain of 33 percent includes credit for co-products such as corn oil and protein feed as well as the energy value of ethanol. The most efficient production and conversion systems are estimated to have a net energy gain of 87 percent.