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BIAB to 2 vessel help

FunkedOut

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I need a hand wrapping my head around moving from single vessel BIAB to a 2 vessel rig.
Particularly setting up the mash profile in BeerSmith.
Not sure if this a process misunderstanding or a software misunderstanding.
Let me explain what's got me confused...  ???

I took a recipe from a recent brew and changed the mash profile from a BIAB single infusion, to a single infusion, no sparge, no mash out profile that came as a sample.
I can see where the Total Water Needed field increased by exactly the amount of difference in the grain absorption rates.
What confuses me is that the calculated/estimated post mash gravity and pre-boil gravity don't change.
In my mind, there is wort left in the grain, not water.

If I mashed this BIAB-style, then lifted the bag out and and squeezed until exactly 0.586 fl.oz. of wort was left in the bag per every oz. of grain (BS default for BIAB), my mind tells me that the wort left in the grain in the bag shares the same SG as the wort in the kettle.
Many times, I've lifted the bag, stirred well, measured the gravity, then squeezed the bag for another half gallon, stirred and measured the same gravity.

So If I now mash this same grist, with the increased amount of water described above, in a mash tun with false bottom, full volume, and simply drain.
I'll take a leap of faith here (since I've never done it) and assume that the grain will hang on to 0.96 fl.oz of wort for every oz of grain (BS default for non-BIAB).
My mind tells me that I have diluted this wort by the water addition and the gravity should be lower.  Something like this:

(BIAB Volume of Water)*(BIAB Post Mash Gravity) = (nonBIAB Volume of Water)*(nonBIAB Post Mash Gravity)

However, BS doesn't change its estimated power mash gravity or pre-boil volume when switching from BIAB mash profiles to nonBIAB mash profiles.

Am I doing something wrong in BS?
Or is my mind playing tricks on me with regard to the added water = dilution concept?

Thanks for reading all that. :-X
 
What you are experiencing is normal for BeerSmith and is easy to understand once you learn out how the program operates. 

BeerSmith simulates your brewing process by solving two parallel sets of equations: one for volume and one for sugar content. 

For volume, the program uses the volume into the fermenter and the process losses as defined in the equipment profile and grain absorption value to figure out how much water you need to start.  When you change a value, such as switching to a non-BIAB absorption value, then the program recalculates the volumes in the system accordingly.

For the sugar content (gravity), the program calculates the balance using the Total Efficiency or Brew House Efficiency.  It applies this value to the volume into the fermenter to calculate how much sugar from the mash will reach the fermenter, then it adds in the process volume losses and associated sugar losses to determine how much sugar must be extracted from the mash in total.

So when you change a process loss in the recipe (such as you did by changing to the non-BIAB grain absorption value), the program recalculates the amount of sugars and changes the mash efficiency to extract that amount from the mash.  By doing this, the program leaves the ending gravity the same, but raises the mash efficiency to account for the additional loss in sugars trapped in the grains with the added water.  If you bring up the two recipes side-by-side with the different mash profiles, you will see a difference in mash efficiency between the two.

While I would prefer to see the program use mash efficiency versus brew house efficiency (as this would make more sense to me since I see my mash efficiency being more consistent and reliable), it is not the way the program is set up to predict the values from your process.

 
Oginme, thanks for your reply.
Everything you typed makes perfect sense.  I follow and agree, except:

Oginme said:
...the program leaves the ending gravity the same, but raises the mash efficiency to account for the additional loss in sugars trapped in the grains...

It does not raise the mash efficiency.  :(
 

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You are correct since the extracted sugars realized remain the same and the added sugars are retained within the mash tun in the absorbed water.  In this case, the realized mash efficiency remains the same.
 
what added sugars?
the grain bill is exactly the same.

more wort is retained in the grain, so more water is added up front to compensate.
is that not dilution?

it seems to me that i'd be making greater volume of wort with the same amount of grain (even though the volume increase remains in the grain).
would not the gravity be lower?
 
i just plugged these numbers into brewersfriend.com's online recipe builder: https://www.brewersfriend.com/homebrew/recipe/calculator
and got the same results as BeerSmith.

Either both calculators are treating what's being absorbed by the grain as water with no sugar,
or my understanding of what's going on is off.

At first glance (of real world, not the BS model), it seems that BIAB is inherently more efficient than no sparge brewing, because less wort (water & sugar) is left in the grain.
 
Sorry for my incomplete explanation. 

There are a number of areas in the brewery which the term "efficiency" is applied.  I was thinking too much in terms of "conversion efficiency" which is the efficiency of converting the starches in the mash tun into sugars.  Under ideal conditions, this number should approach 99+%. 

Once these are converted, the efficiency of removing the wort from the grains is called "lauter efficiency".  This refers to the amount of sugars which can be effectively removed in the wort. 

When we summarize both of these numbers, the term most commonly used is "mash efficiency" which can be more properly termed "mash/lauter efficiency" and is the number that BeerSmith (and other calculators) use to determine the amount of sugars which are extracted for use in making your wort.

Since this number does not take into account the amount of sugars which remain with the grains and associated sugars, you do not see any change in the mash efficiency.  This is where I made that incorrect statement about the change in mash efficiency.  When I said 'added sugars', I was thinking in terms of conversion efficiency and not the mash efficiency and did not properly express it as such.

Because the program does not separate conversion versus mash/lauter efficiency, it will allow the user to set a total efficiency higher to extract more sugar than what can physically be removed from the grains. 

Given this and my original explanation of how BeerSmith (and almost any other program) works, the software will calculate less sugar being left in the grain and with the water associated with the grain than is actually possible, after all it is just a calculation.  This is where my comment about 'more sugars' comes into the conversation.  Since the program only uses the total efficiency to perform its calculations and from this calculates a mash efficiency, it expects that amount of sugar to come from the mash/lauter efficiency and can and will calculate more sugar than can actually be derived from a given grain bill.
 

FunkedOut said:
what added sugars?
the grain bill is exactly the same.

more wort is retained in the grain, so more water is added up front to compensate.
is that not dilution?

it seems to me that i'd be making greater volume of wort with the same amount of grain (even though the volume increase remains in the grain).
would not the gravity be lower?
 
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