What it is
Vorlauf is German for "first runnings," and is now used as both a noun and verb to describe the overall process. In all-grain brewing, it's the second step in the process of lautering, following mash-out. At this point you’re preparing your wort for the boil, and the vorlauf step accomplishes two valuable goals: setting the grain bed for sparging and clarifying the wort.
For homebrewers, one of the big questions is whether or not to vorlauf. You will come across some pretty solid arguments for and against, but for me, the arguments for outweigh those against.
Let’s go a bit deeper into the ins and outs of the process, so you can see why I think it’s a good idea.