Fly sparge question

[chemman14]

I currently do a batch sparge. I plan on going to a fly sparge system in the future when i go to a temperature controlled mash system. I see most people say that you need to keep 1-2 inches of water above your grain bed when fly sparging. Does this mean that your sparge water volume must equal your pre-boil volume? For example if you normally start a 60 min boil with 7 gallons of wort, you will need 7 gallons of sparge water.

 

[tally350z]

You sparge until you reach your preboil volume.

 

[chemman14]

You sparge until you reach your preboil volume.

I understand that but if you maintain 1-2 inches of water on top of the grian bed. Allowing the same ammount of water in as you allow out, wouldnt you need to sparge 7 gallons to get a pre boil volume of 7 gallons

 

[Dougie63]

depends on what you got from your first runnings

 

[tally350z]

You have to take into account the water from your mash..if you have 2 gallons in your mash. Then you need 5 g of sparge water.. Depends on your equipment loss in the MT, grain absorption.

 

[Bobby_M]

The answers so far are a bit cryptic so we'll try this...

There are two camps with fly sparging; those that continue to add new sparge water until the very end of collection and those that stop a little short so that the mashtun isn't filled with water and grain at the end of runoff.

I typically choose a sparge volume that will leave about 3 gallons of water in the tun when I'm done collecting. This is to keep the grainbed flowing nicely right to the end, but without having to dump all that liquid.