Sparging/lautering wort levels

[butterman]

It appears to be standard practice with with fly sparging of all grain mashes to maintain at least an inch of wort above the grain bed when lautering. I'm not sure, but the reasons seems to be to limit the oxidation of the grist as well as to settle the grain bed in order to reduce channeling. Is that correct?

Is the maintenance of such a level just as important with batch sparging since I've seen some recommendations to completely drain the tun for each sparge volume addition?.

[Ozwald]

It appears to be standard practice with with fly sparging of all grain mashes to maintain at least an inch of wort above the grain bed when lautering. I'm not sure, but the reasons seems to be to limit the oxidation of the grist as well as to settle the grain bed in order to reduce channeling. Is that correct?

Is the maintenance of such a level just as important with batch sparging since I've seen some recommendations to completely drain the tun for each sparge volume addition?.

It's just to keep from disturbing the grain bed which could cause uneven rinsing or channeling. Nothing more.

[BDawg]

The whole concept behind batch sparging IS to drain the mash tun, add some sparge water, stir it up to maximize sugar extraction, and drain it again (maybe repeat 1 or 2 more times).
Having an inch of water on top makes no difference.

As said earlier, it's done when fly sparging to help distribute the water coming in so that it doesn't channel, and also to help keep the grain bed from compressing down.

Finally, if you think about it, plain water is lighter than sugary wort. If you gently sprinkle more plain water into the mash tun, it will form a layer above the sugary wort but not mix in with it (think Black and Tan). In some respect this acts like a piston pressing from the top driving the wort out the bottom. The "inch rule" is an easy way to help maintain enough water on top so that pressure at the bottom remains the same and sugar moves downward through the grain bed.