I was curious, why not add my 7.5 gallons of water into my kettle... mash for 60-90 minutes at 150degrees in a bag (deathbrewer partial mash style) and then pull them out and continue?
I'll assume there is a reason but I want to understand why?
Its suggested to mash for an hour with so much water per lb of grain, then sparge (in my case batch sparge) till you get the required volume. However is'nt that the same thing as the full volume to start with?
I'll guess that the original mash water is almost completely saturated with extract and that the fresh sparge is to give the remaining sugars a place to go?