Most of my experiences have involved 3-5 "shadow shifts" in which I observe
the bartender on duty and gradually begin to take a more active role until I'm
doing it all myself. Some of my jobs have provided more formal training,
including workbooks and even classes, particularly Serv-Safe or other
responsible alcohol service programs, but also just formal training in the
recipes.
Here's how I would do it: when a new bartender is hired, I'd give him a
written test to gague his cocktail, wine, and beer knowledge, and do a
role-play scenario to test his real-time acumen. I'd then decide on the basis
of how prepared he seemed what kind and how much training to give him. Someone
who seemed to know as much as one could possibly know without having worked at
this particular bar would get a recipe book to take home and a shadow shift or
two to practice, then another test to ensure he got it all. Someone who
thought a martini should get triple sec (true story from the trenches, that!)
would get the whole training shebang. Or fired, depending on how badly I
needed him.