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.
Why to do it
You might wonder why it’s important to set the grain bed, when you likely already have a false bottom, sieves, and so on. One reason goes back to a homebrew disaster we had several years ago. We were still getting the hang of all-grain brewing and weren’t quite as versed on the hows and whys of the processes, so we didn’t vorlauf before sparging. Grains dislodged from the grain bed, got stuck in the drainpipe, and clogged the mash tun. I’ll spare you the details, but suffice it to say that disaster ensued, and we hated our beer before we even boiled it.
A set grain bed also creates a filter for the sparge water to run through, allowing for greater clarity. Yeah, you can drop a bit of Irish moss into the wort as it’s boiling, but the biggest reason you need clarity is that you don’t want to introduce any grains into the boil. If the grains reach temperatures over 170°F (77°C), they’ll begin to release tannins into your wort. Tannins result in an astringent flavor and haze, both of which you do not want in your final beer.
How to do it
Some of these details may vary slightly depending on your build, so I’ll keep it simple. You will need a sieve of some sort—a large colander, a stainless steel vegetable steamer basket, or a large piece of foil with holes poked in it. Position it above your grain bed.
Now you’ll need a clean pitcher to collect your wort. Slowly open your mash-tun valve to halfway at most to allow the wort to flow into your pitcher. You’ll notice that your wort is cloudy and has a few grains floating in it, which is how it should look at this point. Next, you’ll want to slowly and carefully pour the cloudy wort over the top of your sieve—the point of this step is to set your grain bed, so if you pour the water too fast, it’ll be counterproductive to what we’re trying to accomplish.
Some brewers like to run their vorlauf until the wort is crystal clear, but that’s really not necessary. You can, but really, the most important goal for this process is to clear the wort of grains. A good guideline for how long it should take is 10–20 minutes, and not much longer. Remember, if your wort is still a bit cloudy that can be taken care of later with some kettle finings such as Irish moss, fermentor finings, or cold crashing.
Once you’re satisfied with the appearance of the wort, you can begin to sparge!