When a beam falls in the middle of the staff, the beams point normally
down. However, this behaviour can be altered with the
neutral-direction
property.
{ b8[ b] \override Beam #'neutral-direction = #-1 b[ b] \override Beam #'neutral-direction = #1 b[ b] }
This page is for LilyPond-2.5.11 (development-branch).