[denny]

Efficiency is the other concern, especially if you batch sparge.  Expect at least a 15-20% drop if you go from a 10 lb to 20 lb grist (batch sparging), all else being equal and collecting the same amount of wort.

Boy, I sure haven't seen anything like that.  Maybe 5, sometimes 10 points.

[tygo]

Boy, I sure haven't seen anything like that.  Maybe 5, sometimes 10 points.

I got about 67% with a 22lb grist this weekend.  I'm normally running around 74%.

[nyakavt]

Efficiency is the other concern, especially if you batch sparge.  Expect at least a 15-20% drop if you go from a 10 lb to 20 lb grist (batch sparging), all else being equal and collecting the same amount of wort.

Boy, I sure haven't seen anything like that.  Maybe 5, sometimes 10 points.

From Kai's site: http://braukaiser.com/wiki/index.php/Batch_Sparging_Analysis#Effect_of_the_grist_size_.28weight.29

According to the mathematical model of batch sparging, the efficiency is dependent on the amount of grain used, pre-boil volume, absorbtion ratio, dead space, number of sparges, and relative runoff sizes, provided all other variables are well controlled and 100% conversion is achieved.  If only the amount of grain is being changed, then the model says there will be an 17% difference between the two for a 6.5 gallon (temp adjusted) pre boil, at least if my calculation is correct.  I have found this model to be a bit on the high side of estimated efficiency, I usually get a few points less than predicted.

Personally I've only done a couple of *really* big beers, so I'm not the person to look to for verification of theory.  On the last one efficiency went from a normal 80% down to 65% IIRC, collecting 7 gallons preboil with 23 pounds of grain.  Denny, I seem to remember you saying that you usually have a bigger preboil when you do the barleywine?  Far be it from me to question a brewer that has brewed a *lot* more batches, it's just hard for me to wrap my head around only a 5% efficiency reduction when going from 10 to 20 lbs of grain, all else being equal 

[bbump22]

There's a guy at our tailgate that does this with extract,

Know your lot for next season yet?  We had three homebrewers bring about 10 different varieties to the Spring Game tailgate weekend before last.  That sort of thing needs to be expanded upon.

Dammit - I should have never moved to seattle!  I would be at a bunch of Hokie games with a bunch of homebrews!

[denny]

Far be it from me to question a brewer that has brewed a *lot* more batches, it's just hard for me to wrap my head around only a 5% efficiency reduction when going from 10 to 20 lbs of grain, all else being equal 

Question, question! 

Maybe it's because I can't recall the last time I only used 10 lb. of grain!  My average batch is usually around 15+ lb.

[Hokerer]

Lot 4, we usually bring one keg each.  Where are you guys?

Upper Chicken Hill.  Requested same this season but don't know yet if that's gonna happen.

[Kaiser]

The number of sparges also matter when you go from 10 lb to 20 lb. For big beers I have to sparge twice which gains back a few of the lost points.

Kai

[bluesman]

The number of sparges also matter when you go from 10 lb to 20 lb. For big beers I have to sparge twice which gains back a few of the lost points.

Kai

+1

It's proportional to the concentration of sugar in the mash.

[majorvices]

Boy, I sure haven't seen anything like that.  Maybe 5, sometimes 10 points.

I got about 67% with a 22lb grist this weekend.  I'm normally running around 74%.

That's a bummer. Even on my 1bbl system I get up over 75% efficiency. Same as on my 12 gallon system. Both are batch sparged.

[tygo]

That's a bummer. Even on my 1bbl system I get up over 75% efficiency. Same as on my 12 gallon system. Both are batch sparged.

I wasn't bummed about the drop in efficiency for the bigger beer.  I'd planned it at 65%.  I'm eventually going to get around to tinkering with my system (starting with my crush) to push the "normal" 74% up a bit but that's really just for my ego