Partigyle brewing with batch sparge (10g to 5g)

Tomorrow morning I am planning in brewing a 10 gallon IPA with the following grain bill:
24lbs. 2 row p ale malt
8 oz. carapils
8 oz. crystal 10l
6 oz. crystal 40l

I will be using the the batch sparge method.

Will I have enough fermentables left to add another 6.5 gallons of water and let it sit in the mash tun during the 60 minute boil and get a beer around 1.045 OG? If so, could I add the entire boil volume for the first runnings? If my OG will be lower than 1.045, could I add another lb. or two of the two row to leave in the 60 minute mash?

Interesting idea. I don’t think you’ll hit 1.045 with the second beer without adding some more malt as you suggest. But also think about what you’re doing – you’re basically doing like a 2.5-hour mash for that second beer (except for the malt added halfway in). And this is a second smaller beer anyway, so it’s already going to be kind of wimpy. So that second beer is going to turn out even more wimpy if it mashes for a super long time – very thin and watery. I think the final gravity on it after fermentation would be like 1.002 or something since it is such a long mash time. What I might consider instead is whether you want to collect your third runnings right away instead of waiting an extra hour, bring up to >170 F on your stove in several pots or whatever it takes to stop conversion dead, and then you can worry less about it finishing too thin and dry. But you’ll need to add some serious steeping malts. My wild-butt guess is that you’ll only hit a gravity of around 1.035, maybe even less, and I’d consider adding more crystal malts or dark roasted grains and maybe even up to a half pound of lactose to help bring up the final gravity and give the final beer a little more body. If you don’t want a crystally or roasty beer, then a little extract might be the way to go to boost gravity as required. Best thing might be to test the gravity of the final runnings and then decide what you’ll want to do. Sort of off-the-cuff. But then if the gravity is only like 1.020, you might just decide to stop right there.

In a nutshell, I might sound skeptical but I really don’t know if this is going to work out, as there are a zillion variables, but it should make for an interesting experiment! Let us know how it all turns out if you do try it. I think if you were starting with a bigger beer around 1.100, then partigyle would be a no brainer. But it doesn’t look to me like your IPA is going to be quite that high of gravity.

Dave,
thanks for the input. I guess I never thought about the 2.5 hour mash time for the second beer.
I was planning on a citra pale ale for the second batch. I thought with the amount of grains I had for a 1.065 10 gallon first batch, I may be able to pull a 1.045 5 gallon second batch. i do have a couple pounds of DME and I believe a 1/2 lb to 1 lb of lactose.
It does make more sense to collect the third runnings when I start my first boil. I suppose that would let me know where my OG will be and how much DME/lactose to add.

Just do it! See what happens and report back.
Experimentation is always good.

Add 3# more grain and mash with an extra gallon of water, then set that extra gallon aside. Sparge with the normal volume. Add that reserved gallon back to the MT along with four gallons of water, then take a gravity reading. You can then adjust with a little crystal if needed.