Question about a different sparging method

So I have been doing all grain for a bit now and have been getting around 70% efficiency. I do a double batch sparge.

I was talking to a buddy about it, and he asked if I thought I would get a better efficiency if instead of adding clean water to the second sparge, what if I took the wort that I had already collected and poured it back in the Mash. Would the liquid coming out be a lot more concentrated or no?

I didnt have an answer for him, but I knew that there was probably a reason why no one has mentioned it on homebrewtalk before(that I know of).

What would happen in this situation?

i don't know, but follow thru in your head with your process.

run off ~2.5 gallons of 1st wort, recirculate to get 2.25 gallons of more concentrated.

then what? boil 2.25 gallons? even if it is more concentrated, you're still going to have to add water to your boil kettle at some point. might as well add wort.

That makes sense, but I guess it would be more of an option with a bigger brew where you wouldnt want to have more then 8 gallons of wort to boil down.

Say you want a really high gravity beer, but don't have the capacity to boil that much wort. Then would this method work well?

If the gravity of your mash is say 1.075 and you run off that wort, pouring it back into the mash would do jack squat. The sugar concentration of the liquid trapped in the grain is also 1.075 and at equilibrium. When you put water in as sparge, the sugar that is in the liquid trapped in the grain diffuses out into the water until equilibrium is reached again.

I don't think that you would get a better efficiency doing it that way. Would you get cleaner dishes if you used the dirty dish water to rinse your dishes? Imagine that your grains are the dishes and the mash water is the dish water. You want clean water so that you can create a larger concentration gradient between the grains and the sparge water. This is also why double batch sparge will add a few points over single batch sparge.

Bobby_M said:

If the gravity of your mash is say 1.075 and you run off that wort, pouring it back into the mash would do jack squat. The sugar concentration of the liquid trapped in the grain is also 1.075 and at equilibrium. When you put water in as sparge, the sugar that is in the liquid trapped in the grain diffuses out into the water until equilibrium is reached again.

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makes sense, thanks

I thought I'd chime in with a similar idea I've read about in Radical Brewing by Randy Mosher.

It's called (I think; don't have the book on me) doble-doble, and you basically take a big grain bill, mash half, then use the runnings from this first mash as the strikewater for the second half of the grains.

IIRC Mosher claims it will mean an increased efficiency for high gravity brews without having to gather and boil off as much wort. Also, he recommends capping and sparging the second mash to make a small beer.

I'd like to try it some day, but as a partial mash-er, I don't yet have the equipment. Sounds like an interesting experiment, though!