I've previously just dumped them in too, haven't had an issue yet. With apfelwine the high alcohol % should help keep any nasty-ness from getting in.
Boiling, soaking in star san or soaking in booze, wouldn't be a bad idea either.
How old is this apfelwine? If you're planning to let it age for a long time, the oak will mellow. Some suggest oaking it just to the point where it's a little too much, then aging it. Also it depends on how much you use & what form they're in (cubes, chips, spirals, etc.). If you're using an entire 3oz package in 5 gallons, I would think a month or two should be enough, unless you want a very strong oaky flavor. I'm guessing in something like apfelwine though, you'd want it to be subtle.