One Brew, Two Mash Tuns, Math

[MyCarHasAbs]

I'm making an Imperial Pumpkin Porter (yes I know, it's early in the season) that will be aged another month or so on top of bourbon soaked oak cubes. Pretty stoked about it because in October I'm going to serve it at an office Halloween party.

Anyway, this beer is going to be big. Just shy of 21 lbs of grain. I made an imperial stout months ago that was 18 lbs of grain and that filled my 10 gallon mash tun with water to the brim. No way 21 lbs of grain and water are going to fit.

Luckily for me, I still have my 5 gallon mashtun from before the upgrade. My plan is to use both at the same time and I know this can be done as I've seen a video of a guy making a Russian imperial stout. I'd just have two tubes going to the pot at once.

Math wise, how do you recommend I distribute the strike water and grains accordingly between the 10 and 5 gallon tun?

 

[MyCarHasAbs]

So no one has tried splitting up the gain and strike water between multiple mash tuns before?

 

[McKnuckle]

Why not just do it proportionally? That would be 2/3 of the grain and water in the 10 gallon tun and 1/3 in the 5 gallon tun, using whatever standard mash density you always use. That would be 14 lbs in the big one, and 7 lbs in the small one. The water should sort itself out.

 

[MyCarHasAbs]

Could I suppose. Thought about splitting it directly down the center, 10lbs of grain in each.

 

[McKnuckle]

That would be fine, too. I suggested proportional because it would be more consistent to your process to keep the mash thickness the same in both. Also, with a 50/50 grain allotment, the 5 gal tun will hold its mash temp better than the bigger one (I assume you'd fill it all the way up with strike water). While that is good, it would result in the bigger tun having a less stable mash temp. Again, less consistency between the two vessels.

 

[MyCarHasAbs]

Ohhhh. I'll figure out the exact water measurements once I get the grains and officially weigh everything. Math is not my strength.

 

[MyCarHasAbs]

I have the numbers.

Grains weigh 20.8 lbs. Strike and Sparge calc say 10.8 gallons of water. I'll round that down to 10.
So I'm guessing fill each mash tun up with water about half way and fill the rest accordingly with grains?

 

[Carlscan26]

You'd be better to round the water up to 11 gals. Filling the coolers half way each is only 7.5 gallons of water.

 

[specharka]

Why don't you just use a lower water to grist ratio? Unless you plan on doing a step mash and pulling decoctions, there's really no reason to exceed 1.25 qt/lb. I brewed an impy two weeks ago with 22 lb of grain and it fit just fine into my 10G mash tun. It's not rocket science.

http://www.rackers.org/calcs.shtml

 

[MyCarHasAbs]

I didn't think of the lower water to grist ratio. I brewed this saturday and presuming I make something big like this again I'll probably take that alternative route. My efficiency wasn't as high as I was hoping. I was trying to aim for the 1.10 marker but fell short to 1.080. Presuming it hits 1.010 I'll take the 9% range. Might go a little higher after I introduce a few secondary ingredients involving bourbon in about 4 weeks.