Will there be a difference in pre-boil gravity in these situations (in theory and practice):
1) I mash with the *exact* amount of water needed to hit my pre-boil volume on the mark. For instance, 3qts of water/lb grain. No sparge. Lauter slowly to boil kettle to get 7gallons pre-boil.
2) I mash with the same amount of water as above (3qts/lb), but this time, I fly sparge while it's lautering. Lauter slowly (same rate as sparge) to boil kettle to get 7gallons pre-boil. [I assume that the sparge water will push the mash wort down, so that only mash wort moves into BK, and all sparge water stays in MLT. Is this correct?]
3) I mash with less water, say 1-2 qts. Fly sparge. Lauter (slowly) to boil kettle to get 7gallons pre-boil. [In this case, "sparge water" will end up in the BK. Though that sparge water should have rinsed the grains of remaining sugars]
I'm trying to get a better idea of mashing/lautering in regards to water volume. Thanks for any help!