[syncopadence]

Sorry if this is a stupid question (I'm a newbie to all-grain), but I'm wondering what the different volumes do?  I've seen on here that usually you use a ratio of 1.5 gallons of water per pound of grains.  So would that mean if I have 12 pounds of grain, I should be doing 4.5 gallons of water for the mash, and 2 gallons for sparge?  I wrote down 3.75/2.75, and the guys at my local brew shop think it's ok, but this would deviate from the aforementioned formula.
Thanks in advance for any help!

[a10t2]

12 lb of grain will absorb ~1.5 gal (0.12 gal/lb), so you need to sparge with enough that your total water volume is your pre-boil volume plus 1.5 gal. e.g. If you're trying to start the boil with 6.5 gal, you would want to infuse another 6.5 + 1.5 - 4.5 = 3.5 gal.

In practice, the liquor-to-grist ratio (1.5 qt/lb in this case) doesn't make much difference. If you're batch sparging, you want to try to get the two (or more) runoff volumes to be equal. For fly sparging, you want to mash as thick as you can work with.

[syncopadence]

12 lb of grain will absorb ~1.5 gal (0.12 gal/lb), so you need to sparge with enough that your total water volume is your pre-boil volume plus 1.5 gal. e.g. If you're trying to start the boil with 6.5 gal, you would want to infuse another 6.5 + 1.5 - 4.5 = 3.5 gal.

In practice, the liquor-to-grist ratio (1.5 qt/lb in this case) doesn't make much difference. If you're batch sparging, you want to try to get the two (or more) runoff volumes to be equal. For fly sparging, you want to mash as thick as you can work with.

So for batch sparging for this one, 4.5/3.5 would work? 

[a10t2]

Assuming 6.5 gal is your pre-boil volume, yes.

[micsager]

For fly sparging, you want to mash as thick as you can work with.

Can you explain this more?  I brew 1bbl batches, and the grain bill is between 65 and 90 pounds depending on recipe.  I almost always just add 20 gallons for mash, then roughly figure each 10 lbs of grain will retain a gallon of water, and fly sparge the right volume to hit 36 gallons.  Most sessions, I hit the 36 right on.......

[a10t2]

Can you explain this more?

I should have said that to optimize lauter efficiency, you want to mash as thick as possible. If the total water volume is constant, reserving more liquor for the sparge will more thoroughly rinse the grain bed.

At homebrew scales (or nano scale, for that matter) it doesn't really make much of a difference, but at bigger breweries it's nice to get that last few percent, if only because it translates into less grain you have to lug around.

[Guenther]

Assuming I have an HLT with the same size (or even a little bit smaller) than MLT, I just get it full of hot water, than while sparging it depends on what is my goal for that beer. Sometimes I just keep measuring the pre-boil volume that I want, in cases a couple gravity points below or above wont hurt and I want to achieve an specific color. Other times when I want to achieve an specific OG, I keep measuring the pre-boil gravity.

In any of these cases, how much hot water I have, and how much did I use in during the sparge? I don't know, because I don't need too. Once the boil kettle is getting close to the volume/gravity I want, I just stop adding water and let the rest of the wort I want get to the boil kettle.

Usually, just a few liters of hot water stay on the HLT (which I use for other purposes like washing stuff or re-hydrating yeast), and the rest of the wort that lasts in the MLT once you get used to this technique is really small volume. Basically.. doing that I never have to worry about sparge water volume... either for Fly or Batch Sparge (depends on the equipment I'm using).