was over at a friend's house today just seeing his brew process and an interesting question came up. we both have fly sparging systems, but we use them slightly differently.
when i sparge, i keep the water level topped up over the grain the whole time. eventually i pretty much drain my entire 15g hlt into my mash, and get my 15 or so gallons in the kettle. when i'm done, the level of the liquid in the mash is still above the grain bed.
when he sparges, he keeps the water level topped up over the grain, until he gets close to his volume. then he lets the wort drain out of the mash/lauter tun, ending up with 15 or so gallons in the kettle, but when he is done, there is no liquid left in the mash.
i've been doing it my way as i thought that is how it should be done, and he's been doing the same thing for the same reason. it seems like there might be some differences in efficiency as well as ph in choosing one of these methods.
does anyone have any info / opinions? i've looked in how to brew, and this question seems to not be covered in the fly sparging sections.