Calculating/predicting parti-gyle densities and resulting brews

[unclebrazzie]

Posted on another forum as well, but sharing = caring

I'm planning another parti-gyle / split-batch brew day.
My aim is to brew a 1.090 OG wee heavy from first runnings (plus extras), and a 1.054 OG sour from second runnings.

Since I'm brewing on a primitive 30 liter rig (double plastic filterbucket mash tun, 30 liter kettle), parti-gyling seems like a good way to achieve a good, strong wort for the first, with enough yumminess in the last.

Here's my approach.

Using Randy's tables and taking the 50/50 approach, I decide I need a 1.081 theoretical brew, which will yield 1.108 in the first half, and 1.054 in the second. 10 liters each, so a 20 liter 1.081 mash should yield all the fermentables I need for both brews.

Result: 10 liters at 1.108 (Wort 1)
10 liters at 1.054 (Wort 2)

I'm about .010 SG over my 1.090 mark, because I want the scotch to be peated, without peating the sour second runnings, so I'm doing a small second mash of just whiskey malt, yielding 5 liters of 1.055 wort.

Result: 5 liters at 1.055 (Wort 3)

Combine worts 1 and 3 to yield 15 liters at 1.090. This will be the wee heavy.
Wort 2 is pretty much good to go, but I might decide to add some extra wheat malt and/or starchy grains to the mash tun and actually mash again instead of just sparging. This'll yield a denser wort, which I can then dilute to have more wort at the desired gravity.

Couple of sidenotes:

*) gravities are all calculated pre-boil. Post-boil, they'll be higher (especially the wee heavy which I intend to boil for about two hours). Dilution at the end of the boil will be necessary to get them where I want them.
*) I'm complicating things by wanting peat in one but not the other. It'd be easier if I could just re-use the same grist, but where'd be the fun in that?
*) another reason I'm going through the trouble and mathematical calistenics of parti-gyling is that I'm going to be using a lot of malt to get the wee heavy at 1.090. I could brew more than 10 liters, but then I'd need a bigger mash tun to be able to mash and sparge properly. It's a balancing act between malt, mash tun space, and yield volume.

Any thoughts on the above?
I'll be posting recipes for both brews later on.

 

[signpost]

Sounds like fun. I've done a couple partigyle brews, but never got that specific about calculating the gravity ahead of time. I just went for it.

Without actually doing any math, what you described seemed to make sense. I think it's definitely worth it to try and get a small beer from the grist, when you are already making a big beer. It's just a wasted opportunity if you don't.