Eluze,
I forgot to make sure that the lilypond-user list was in the "To" field when I replied as follows:
>Fabio,
>Try \stemUp or \stemDown. In English, the beam is the horizontal line, so you want to tell the stem (vertical) to >move and the beam will follow.
>Best Wishes from a fellow bass player!
>Mark
I see that you gave the shotgun answer with a pointer to the the documentation, and I gave the rifle answer with the command but no pointer to documentation. For my own progress in learning, what other way is there besides \stemUp, \stemDown and \stemNeutral? I couldn't find anything else in my cursory perusal of the docs.
Thanks,
Mark