**4. Pretreatment of lignocellulosic biomass**

Pretreatment processes are applied to lignocellulose prior to hydrolysis and fermentation in order to:

• Increase the amorphous regions, which is easier to be hydrolyzed than crystalline cellulose.


Physical, chemical, and biological pretreatment methods are used in pretreating lignocellulose. For a classification of pretreatment methods, the following are a brief summary:
