Biochemical Conversion<br />Cell-Wall Recalcitrance<br />
Source: US DOE
One of the greatest challenges in converting feedstock into ethanol is separating the lignin from the cellulose and hemicellulose. We call this cell wall recalcitrance. Recalcitrance is the natural resistance to degradation or breakdown. The lignin molecules, as you recall, form a protective coating to shield the cellulose and hemicellulose from the enzymes that we want to use to break them down. In addition lignin is a source of chemical by-products that can inhibit the conversion of sugar into ethanol. As I indicated, this is a great challenge to attaining a viable cost effective cellulosic biofuel industry.