[brewandski]

Everything I read about batch sparging says to "drain" the mash tun and add the sparge water.  Do you actually drain all the wort out or stop and leave some water in so that the grains are still wet?  I guess I am wondering how much to drain the mash tun?

[Malticulous]

For maximum efficiency you want to drain it as dry as possible.

[denny]

Everything I read about batch sparging says to "drain" the mash tun and add the sparge water.  Do you actually drain all the wort out or stop and leave some water in so that the grains are still wet?  I guess I am wondering how much to drain the mash tun?

Drain until there's nothing coming out any longer.  If you feel like it, you can tilt your cooler to get the last bits out.  How much you get depends on the cooler you use.  I seldom get more than a few cups by tilting, others get a couple qt.

[euge]

With the first run I stop when it's a small trickle and start the second sparge just to save time. Then I try to get as much as possible.

[bluesman]

The first runnings are the most precious and you should try to get as much as possible. I usually lauter until there's only a trickle. The first runnings are the most concentrated of the two and should be thouroughly drained.

[brewandski]

I have heard of a risk of astringency from exposing the grain bed to air.  Is this just for extended periods of time?

[denny]

I have heard of a risk of astringency from exposing the grain bed to air.  Is this just for extended periods of time?

I don't believe it's true at all, and I'm hard pressed to think of a reason it would be.  You certainly don't need to worry about it as a batch sparging homebrewer.

[brewandski]

Thanks for all your quick responses!