Biochemical conversion comprises breaking down or “cracking” biomass by using physical, chemical, enzymatic and/or microbial action, to make the polymeric carbohydrates of the biomass (hemicellulose and cellulose) available as (fermentable) sugars, which can then be converted into biofuels and bioproducts using microorganisms (bacteria, yeast, fungi, etc.) and their enzymes or chemically converted using specific catalysts. A general overview of the different process steps of the biochemical conversion of lignocellulosic biomass is given in Figure 2.2.

Firstly, a reduction in particle size is often needed to make material handling easier and to increase surface/volume ratio, so as to enable better accessibility of the processed material in the next pretreatment step. Size reduction is most often done by a mechanical process such as crushing, milling, chipping, grinding or pulverizing to the required particle size.