Understanding mash settings

I have been tweaking the mash settings and based on a Denny Conn podcast I am aiming to get equal volumes out of the mash tun.  I have a 10 gallon cooler mash tun and am making an all grain stout recipe with a grain weight basis of 11.13Lbs.  I have my equipment profile dialed in and the mash tun has a deadspace of 0.75 gallons.

The mash setting I am using for this is:
- Single infusion with two steps, full body, batch sparge
- I have the "Drain Mash tun before sparging" ticked, as well as "Use equal batch sizes"

BeerSmith is saying to mash in with 16.91quarts, drain the mash tun and then sparge with 5.35 gallons.  The mash absorption is calculated at 1.34 gallons.

So the initial runnings will be (16.91/4) - 0.75 deadspace - 1.34 absorption = 2.1 gallons.  Then I sparge with 5.35 gallos and end up with 5.35+ 2.1 = 7.45 gallons which is correct.  I need 7.5 gallons in the kettle for my equipment profile.

The question I have is that I would have thought that for equal batch sizes, I would be looking at 7.5/2 or 3.75 plus the absorption and deadspace losses.  So 3.75+0.75+1.34 = 5.8 gallons/23.4 quarts.  That would result in 3.75 gallons when I drain the mash tun and then I would add another 3.75 gallons to end up with a total of 7.5 gallons.

What am I missing?  Is it that adding 5.8 gallons into 11lbs of grain would make too thin a mash consistency and it is more important to achieve the recommended 1.25 quarts/Lb thickness?

Thanks,

Paul

Just add the remainder too your sparge water. Even a couple of quarts difference in that size batch won't make a noticeable difference in efficiency. By adding it to the sparge instead of the strike volume you won't need to recalculate anything.

The box for 'use equal batch sizes' actually refers only to the batch sparge.  If you are limited in space in your mash tun that the program needs to do two sparges, it will make those two sparge steps equal in volume.  It does not affect or adjust the initial infusion volume nor adjust anything to accomplish equal running from mash or sparge.

So, I think you have the basic calculations for figuring your initial infusion and sparge volumes in your calculation in your statement: "I would be looking at 7.5/2 or 3.75 plus the absorption and deadspace losses.  So 3.75+0.75+1.34 = 5.8 gallons/23.4 quarts.  That would result in 3.75 gallons when I drain the mash tun and then I would add another 3.75 gallons to end up with a total of 7.5 gallons."

I set up my infusion step and batch sparge for equal runnings on an average recipe that I would brew.  From there, like BOB357 stated, a quart or two difference either way really doesn't matter much.

For your initial infusion, most of my brews are full volume BIAB, so a mash thickness of 2.1 qts/lb is heavy compared to my BIAB mashes.  What I have seen from the 1.25 qts/lb mash thickness is that is an approximate minimum for mashing to allow enough starches and enzymes to become soluble and accomplish efficient conversion.  Any thicker and there is just not enough water for enzyme transportation and to allow efficient wetting of the grains.

Got it.  Thanks for the explanation guys.  Got it.

I will try this approach in today's brew.

Paul