OK, so last time we talked about partigyle and the myth of free beer. I discussed how to figure out roughly what you can expect from second-runnings beer and ways you can improve it. I also mentioned (at least, I think I did) that the big problem with this is that it's very hard to plan ahead and brew a second beer of your choosing. While this is not necessarily a huge problem for some people (the "hey, it's beer, I'll drink it" crowed. You know who you are.. ) some of us like to have the beer we LIKE on tap, not just the beer we ended up with...
So, how do you make a deliberate second-runnings beer? Or possibly a better question: How do you make two beers out of the same mash?
Let's say that you want to make two beers, a porter, and an IPA, and being a complete lush, you want a full keg of each (That'll just about tie you over for the weekend, wouldn't it? Yeah, I thought so...) Full keg is about 18L (we're talking cornys here), so you need about 36L of beer at the end of the process. Call it 40 with losses and trub. How do you make it?
Let's start by taking a look at the two beers that you want to make and look for any commonalities, I deliberately chose two beers that seem very different for this example (cause I don't believe in coddling). So...
For the IPA:
OG: 1.065. FG: 1.012 IBU: 64
85% Two row, 5% Munich, 8.5%, Crystal 15, 2.5% Crystal 40
On my system I get about 72% efficiency, so that means I need about
4.75kg Two row, 300g Munich, 450g C15, and 100g C40. (For a 20L batch)
For the Porter:
OG: 1.052 FG: 1.013 IBU:27
74% Two row, 10% Brown Malt, 10% Crystal 40, 6% chocolate malt or
3.4kg Pale, 450g brown, 450g C40, 285g Chocolate.
Of that, the percent that comes from the base malt can be calculated per-beer, so for the IPA 85% of 1300 = 1100, and for the Porter 72% of 1040 =750. Together, that means that if we wanted to do a mash of Two Row only, we would need a mash that can provide 1850 points.
Now that we have that number, we can decide how we want to achieve this amount of sugar. Basically, we have two choices: We can increase the gravity, or we can increase the volume.
Increasing the volume goes like this: We need 20L of 1.055 wort for the IPA, and another 13.5L for the Porter. This is because 1.055 is the relative part of the base malt in the IPA (with another 1.010 coming from the steeping malt.) For the porter, we will dilute the 13.5L with 6.5L of water to achieve 20L of 1.037, which is 72% of 1.052 - the relative part of the base malt there. To double check that figure we can calculate back: 55*33.5=1842.5. Close enough.
Increasing the volume has advantages: A lower wort gravity means better hop utilization, for example. But the biggest disadvantage of this idea is that you have a lot of wort to boil. For a 33.5L final batch size you'd probably have to bring something in the neighborhood of 40-42L to a rolling boil. Most of us who do 20L batches don't necessarily have the capability to boil that much liquid, both in terms of kettle size or heat, and trying to brew that size batch on a system that's dialed in for half of it is just asking to screw things up.
The other option is to increase the gravity: We know we need a total of 1850 points in our kettle. For a regular 20L batch size that makes 1.0925 OG (1850/20), which is the size of a good size DIPA or RIS, but not out of reach for most homebrew systems. Of course, as with high gravity brewing you have to take into account lower efficiency and utilization, but to my mind this is still the better option. Especially if you've brewed "big beer" before and are familiar with how your system functions under those conditions.
So that's those are the basics. So far I've only talked about the base malt, and there're still the questions of the steeping grains and the hops, but this post is already getting long, so I'll talk about those things in part three of this series...