Fly Sparging volume confusion

Howdy,
I seem to be having a hard time hitting either my gravity numbers or pre-boil volumes and I wonder if part of it isn't a fundamental misunderstanding about Fly Sparging technique.  Typically, when I hit my volume, my runnings are still way above 2 degrees Plato and my pH is nowhere near 5.8 which is where I usually draw the line.  So, I keep going, not wanting to give up those sugars.  This weekend for example, I was making an 11 gallon batch, expecting a pre-boil volume of 17.3g and I stopped runnings at 20.5g with a Brix of 5 and a pH of 5.4.  To correct my volume I boiled the wort down to 17.3 gallons (about 90 minutes) and then started the "real" 90 minute boil with it's hop schedule.  The post boil volume was right but my gravity was off.  Expecting 1.080 and got 1.090  (Obviously, I'm getting the sugars out so I don't *think* I'm sparging/lautering too fast... am I?).  Not a big deal really.  I added a gallon of top up water and my gravity is fine now; though I have a gallon more wort than I expected.

Clearly I'm missing something.

The only reason I'm posting this in the BS forum is this:  In BS2, in the Mash tab of my recipes, I see "Fly sparge with x gallons" but in every other discussion on fly sparging I've always read the simple guidance: Always keep an inch or so of clear water over the grainbed".

So, my over-simplified question is, "Which one is right?".  Should I "Always keep an inch of clear water over the grainbed" until my runnings tell me to stop?  Or, do I "Fly sparge with X gallons" while keeping an inch of clear water over the grainbed until I run out of sparge water (while continuing the lauter)?  A side question: If the answer is to just keep an inch of water over the grainbed, what is the value of the sparge water calculation in BS?

Note (in case it's helpful): My MT is a 40 gallon Stout MT with a diameter of 20 inches.  I am lautering at 1 Qt per minute.

Thanks for any help,

G

Higher gravity beers often result in higher final runnings. I make a 20P beer that always has last runnings of 3 & 5 Plato.  Anything under 17P tends to get to 2P at the end of sparge.

gbarker121 said:

In BS2, in the Mash tab of my recipes, I see "Fly sparge with x gallons" but in every other discussion on fly sparging I've always read the simple guidance: Always keep an inch or so of clear water over the grainbed".

So, my over-simplified question is, "Which one is right?". 

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Both. Just pick one.

Should I "Always keep an inch of clear water over the grainbed" until my runnings tell me to stop?  Or, do I "Fly sparge with X gallons" while keeping an inch of clear water over the grainbed until I run out of sparge water (while continuing the lauter)? 

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Either method is valid. I keep water in the mash just to keep consistent head pressure on the flow. A gravity feed system the elevates the mash above the kettle can be run dry, if you wish. The entire reason for keeping the inch of top water, and/or using a sprinkling sparge system is to simply not drill a hole in the mash. The extra inch keeps the mash "floating" instead of compacting. Once you have all the water in the mashtun, it's perfectly fine to let it run dry.

A side question: If the answer is to just keep an inch of water over the grainbed, what is the value of the sparge water calculation in BS?

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If you don't want to let it run dry, then this is effectively mash/lauter "dead space." That can be accounted for and BeerSmith will add it to the strike water and subtract it from the sparge.

Note (in case it's helpful): My MT is a 40 gallon Stout MT with a diameter of 20 inches.  I am lautering at 1 Qt per minute.

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The sparge rate seems appropriate for your volume. Total sparge time should be 60 to 90 minutes.

I'll chime in here and hopefully be a bit helpful.

BS is telling you your sparge volume that you need in order to hit your preboil volume based on all your other numbers: grain mass, mash volume, MLT volume, dead space, etc. If you follow the calculations of BS you will (or should) meet all your numbers _AS LONG AS_ you have input the correct information to BS. You are the one who needs to tell BS how you brew, not the other way around.

For fly sparging, yes, keep an inch of water above the grain bed but if you are following the calculations then once you run out of your sparge water just let the MLT run dry. Magically you should end up with the calculated pre-boil volume.

What brewfun mentioned is correct: larger gravity beers will have higher end of lauter readings due to lower efficiencies. That's just a given. So monitoring your end of lauter reading and continuing to sparge/lauter _based_ on that will give you "incorrect" readings based on the BS calculations. Increasing your volume and then boiling that down to your originally desired volume is not doing anything more for you than wasting energy and time.

If you plug in all the appropriate and accurate variables to BS you should end up meeting all your numbers or get pretty darn close. Those variables are the huge key to unlocking how BS can help you best. If you're not doing that then your numbers are going to appear pretty darn wacky for a while.

As an aside: I've never calculated my sparge water volume. I do fly sparge but I just heat "a volume" of water that I know will be more than I need. I sparge/lauter until I reach my calculated/desired volume in the BK. Sparge water that I have left gets used for clean up and chasing beer through my lines at cooling in.

I hope that is somewhat helpful for you.