So I'm getting ready to brew my first AG Imperial Stout tomorrow (Prairie Bomb clone - 27 lbs. of grain) and I'm looking for any tips that the hive might be willing to share before I jump in.

I'm building up a keggle today to use as the mash tun since my old Igloo cooler can't handle all that grain and water (almost 9 gallons of mash water).
I'm planning on using a chugger pump to Vorloff the mash for 10 minutes or so, then sparge with 3 gallons of water.
60 minute boil with an OG goal of 1.14
Double batch of WLP001 going in the starter flask shortly.
Going to O2 the wort for 30 seconds or so before I pitch the yeast.
After fermentation I'm adding cocoa nibs, vanilla beans, coffee and Ancho chilies in the secondary.

I'd appreciate any tips or things I should look out for as this is my first batch this big.

TIA!

I came to post "don't forget chilies", clearly you are already there. Cheers.

Care to share the recipe?
This sounds like something I need to try

The problem with mashing in a keggle is heat loss.
When you use a cooler, you are getting maybe 1 deg of loss in 1 hour. With a keggle, it could be 10 degrees. I tried mashing in my boil kettle (using BIAB) and I was never able to get it to work correctly.
Using direct fire to bring the temp back up can kill your amylase enzymes.

27 lbs of grain? So you need at least 27 quarts of strike water, more realistically 34 quarts which is 8.5 gallons.
Also for that big of a beer, make sure you hold your mash temp for at least 1 hour.

Yup, I have a couple of thermal blankets that I'll be using on the keggle. I've done this previously (before I got the cooler) with pretty good success, but not with a batch this big.
Previously I upped the mash water temp to 170 before stirring in the grain and it settled out at 150-155 for the hour duration with the blanket. I'm thinking this time I'll need to up it a bit more to compensate for all the grain bill.

For those interested, I'm loosely following this recipe - Clone Linky

Go big or go home

I use 27 lbs of grain and 8.5 gallons mash water for my IPAs and it will fill a keggle up to about 1.5-2" from the top

My strike is 168 and with 70 degree grain that will get me to 152-154 every time. I have a insulated mash tun. Its a keggle with 2" foam strips wrapped around it. and a foam top. it might lose a degree- maybe 2 if its really cold/windy.

I would suggest trying the foam, 2" strips made from 1" material with overlapping layers and held on temperaly with duct tape will do amzing things. it will only cost about 30 bucks

ETA strike water temps dont have to be "upped" for large grain bills, as you add more water with more grain. Generally around 165-170 will always get you to 150ish.  my 5 gallon 4% light beers all the way to the big IPAs take around 165-168 strike

So I followed djkest's advice and picked up a 70 qt rectangular cooler this morning, and retrofitted the round tun's fittings to it. 170 degree strike water netted 153 degree mash temp, and after a 3 gallon sparge and a 60 minute boil I netted 5.5 gallons with an OG of 1.102. A bit lower then I was shooting for but I'll deal with it.

I'm looking at 2 weeks in the primary and another 3 in the secondary with the adjuncts. Needless to say I'm stoked at this first go. Updates to follow ??

Thanks for the tips gents!

153 degrees is a very nice mash temp to hit. Should give your yeast plenty to much on. I am in the process of buying a larger cooler to update my system as well. I hear Walmart has sales on coolers from time to time. Good luck! I hope you have a lot of yeast!

Also if you fail to fit your desired OG, it's always possible to add DME to bring that up a bit. The best way to figure out if you'll need DME is by taking Pre-boil gravity and volume measurements.

Update -  after 2 weeks in the primary, I racked to the secondary last night with a FG of 1.022. Looks like an ABV of close to 10.6.

I added the following adjuncts before sealing the secondary up;

1 cup of Jet Fuel coffee beans
2 Ancho chilies cut in thirds
3 Vanilla beans
8 oz. of coca nibs
1 oz of light oak chips that had been soaking in Pyrat rum for a week

I'll taste every week for the next 3 and see how it mellows.

I've got a couple of 2.5 gallon kegs that I plan to use for the final product - 1 on CO2 only and one on beer gas for a nitro pour.

Update to follow!

Soooo, after sitting in the secondary for three more weeks, I finally racked it to a keg this weekend. It doesn't quite have the Prarie Bomb mouth feel, but damn it tastes fantastic!

I'm carbing the keg to 1.5 volumes of CO2, and intend to put it on Nitro in a couple of weeks when I'm back in town.

Meanwhile, I've got an Oskar Blues Old Chubb Scotch Ale clone carbing up, which should be ready to pour on Friday. I had to brew something while I was waiting for the PBomb to settle.



If it turns out to be good I'll post the recipe.

OMG it's good! Real strong coffe flavor, so next time I'll cut the amount of beans back to 3/4 cup.

The recipe is almost identical to the link above, except I substituted coffee malt for chocolate and used the stated adjuncts.

I have it on nitro which helps with the creaminess, and I think I'll be doing this one again next winter.

Next up is a Pliney clone using whole hops in the mash ( More Beer Pliney clone recipe).

Damn good job OP. I love PA Bomb

Damn, me too! We should hang out

Seriously though, now that's it's sat in the keg for a bit, it's melded quite nicely. Since
It's getting warmer here in Texas we've been drinking pale ales, but we hit the stout tonight
And the coffee has faded and the cocoa is more pronounced.

Actually I'm extremely pleased with the outcome. If you're thinking about brewing this,
Go for it!