Most of the description is written in the passive voice (such as “Feedstocks for biochemical processes are selected . . .”). The passive voice is appropriate because the focus of this process description is on what happens to the materials, not on what a person does. By contrast, in a set of instructions the focus is on what a person does.

Source: U.S. Department of Energy, 2013: www1.eere.energy.gov/bioenergy/pdfs/biochemical_four_pager.pdf.