"Biomass recalcitrance" is a term given to second-generation (lignocellulosic) biofuel feedstocks which are not easily amenable to the pretreatment processing step in the "cellulose-ethanol" production process. "Recalcitrance" is attributed to the tight lignin wrapping which prevents the accessibility of the biomass carbohydrate fractions (cellulose/hemicellulose). The carbohydrate fractions must be accessible to enzymatic hydrolysis so that these can be converted to simple sugars that are eventually fermented into ethanol. Extreme (and energy-intensive) pretreatment processes (such as high temperature in acidic, alkaline or oxidizing conditions) are often used to break biomass recalcitrance. In order to reduced the high pretreatment costs associated with the pretreatment of recalcitrant biomass, scientist are starting to focus on developing genetically-tailored bioenergy crops with modified lignin contents in the biomass. The lignin modification allows less extreme pretreatment conditions during ethanol processing. An international team of scientists from the United States and China report the use of genetic modification (of a lignin biosynthetic pathway) and "low phytic acid mutation" on barley and wheat straws, in an effort to develop biofuel feedstocks with low biomass recalcitrance. They found that "the change of fiber structure caused by mutation and genetic modification significantly improved "hydrolysibility" of the straws, and further enhanced cellulosic ethanol production". The full paper is published in the journal, Biomass and Bioenergy (URL above)