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Mash tun Dead Space, recoverable dead space and grain absorption

atlref

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I am trying to get a better understand of the proper way to go about my equipment and advance settings dialed in.
My setup -  3 vessel all grain Rims. Boil kettle 20 gallon Blichman G1 Mash tun 20 gallon Blichman G1 w/ Blichman false bottom, HLT 15 gallon Blichman G1. HLT and BK are gas fired.  2 chugger pumps and 5,500 ULWD heating element ( running on 120V so +/- 1,400 watts) for rims tube.
I have measured my true dead space ( unrecoverable water left under false bottom) = .1 gallon.  I have .5 gallons of recoverable mash dead space ( pump, lines, rims tube).
Process- Mash in recirculate for 60 min. and drain to BK. Add sparge water, stir, recirculate 10 -15 to clarify and ramp temp to 168 for mash out and drain to BK -  AT THIS POINT I would like to hit my pre-boil volume  -  I do not want to go and chase the last .5 gallon that will still be in my rims tube and lines leading into MT ( I know I could pump additional water from my HLT thru the lines to push the wort into the MT before draining but prefer not to.)

SO my question is -  Do I need to change my dead space to include this .5 gallons ( so it would now be .6 gallons) that is left in the system and at the same time decrease my recoverable dead space  to 0 ?  If I do this will it effect my water to grain ratio in the mash ( I believe the purpose of the recoverable mash dead space is to help keep your water/grain ratio in proportion).

Question 2 -
to compensate for the above scenario I have been increasing my grain absorption number . If I make the above changes should I go back to the standard .96 fl oz/oz and use an excel sheet to track and adjust absorption and adjust accordingly?

Thoughts comments will be appreciated.
 
It sounds like you are pretty much on the right track in terms of defining your process.

If it were my system running it the way you are, I would add that additional amount in the mash tun dead space.  Since the water left behind will really be separate from the grain absorption and I really would not want to have this volume change due to differences in the grain bill, but more of a planned excess which is not drained out of the system. 

I would validate the grain absorption figure [mostly because I am a process geek and like to define these losses for my awareness] by monitoring total water into the mash tun (infusion + sparge) versus the volume collected in the boil kettle.  That figure less the wort volume planned on being left behind should be your grain absorption which can be tracked over a few brews to make sure that the setting is good enough to rely upon. 

 
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