fly sparge question

[jp1316]

So I am doing my second all grain beer today and this time I am going to fly sparge instead of batch sparge. My only question is do I fill the hlt with the exact amount of sparge water I think I will need to get my preboil volume(so I would let the water in the mash tun drain all the way out)? Or should I just fill it with more then I will need and keep the water in the mash above the grain bed(1-2inches) until I collect my preboil volume? Thanks!

 

[ChemE]

The latter unless you're very confident about grain absorption and other losses. It is better to have too much than too little.

 

[jp1316]

Thanks, I just wasn't sure if I had to drain the water from the grain bed.

 

[TwoHeadsBrewing]

If you haven't used it yet, I'd try the BeerSmith program. I've found it to be pretty close on required volumes when fly sparging. Usually, I'll add another gallon for sparging just to make sure I don't come up short. It's pretty nice, the "brew sheet" prints out the steps for the brew day including volumes and temps for mash and sparge.

Here's a sample printout from my last brew:

Mash In: Add 6.43 gal of water at 163.8 F
Mash Out: Add 3.63 gal of water at 196.6 F
Sparge with 6.86 gal of 168.0 F water.