BIAB Bag Squeezing Question

[mr_beer]

After doing reasonable research on BIAB bag squeezing I think the consensus is:
?   Base malts and low color and caramel malts give up their extract easily, so squeezing the bag gives you retained wort instead of retained extract. Squeeze as much and often as possible.
?   Roast malts and high color caramel malts, like Special B, don?t give up their extract easily, and aggressively squeezing the grain bag will release more of the roast compounds into the wort. These compounds can taste quite harsh. 

To avoid the harsh compounds my notion is that roast malts and high color malts should be crushed separately and put into another bag inside the pot with the base malts.   Remove that bag and drain only.  DO NOT squeeze.

Any opinions or suggestions?

[Oginme]

I am not sure of your sources and where the 'consensus' opinion is formed.

Here is my learning from doing over 240 BIAB brews:

Grains will give harsh flavors when the mash pH is not controlled to less than 6.0 pH during the mash process, 
Mashing most specialty grains will result in a greater extraction of sugars and color than mash capping or steeping,
Roasted grains will give a stronger roasted flavor when mashed with the other grains versus capping the mash with the roasted grains or separately steeping the roasted grains,
Over use of roasted grains will also give a harsher flavor, which is why most of the darker grains are recommended at lower addition levels of the grist,
To get the same color, the use of roasted grains which are added as capping the mash must be increased since the amount of the extraction is less when not mashed with a base malt,
This same lower extraction when steeped or mash capped additions are used applies to caramel/crystal/toasted malts as well,
If your conversion is complete and the wort has equilibrated inside the grain particles and in the wort, then squeezing the bag to force more of the free wort out of the grains will result in no change in the gravity,
If your conversion is incomplete, then squeezing the grain bag will result in unconverted starches being extracted from the grains,
If you have a short mash where the wort is not in equilibrium with the water inside the grains, then you will see some increase in gravity of the wort squeezed out of the bag versus the wort already collected,
The majority of the wort which is collected from squeezing the bag is wort which is contained not in the grains, but between the grain particles, 
Simple squeezing forces the grain particles closer together and frees up the wort trapped in this interstitial region thus giving us more wort,
Applying greater forces than simple hand squeezing will partially compress the grain particles and reduce the amount of wort trapped within them,

All of these factors I have tested and measured many times in figuring out what works best for my process, maximizes my extraction, and which actions bring about the biggest improvement in extraction with the least amount of work and which require greater effort for minimum gain.  In the end, squeezing or not is a personal choice.  If you are getting harsh flavors from dark caramel/crystal or roasted grains in your system, you can choose not to squeeze and that is fine.  I would suggest that there is another cause for the harsh flavors to be extracted which is unrelated to squeezing.

[mr_beer]

Thank you for your fulsome reply -- it had actual facts backed by actual experience. 

The consensus opinion I referred to was my summary view after reading a variety of sources, some with writers of stellar reputation, others not so much.  The two bag approach was my formulation, not anyone's recommendation. 

To be honest, I have not noticed any harsh or unpalatable flavors in my batches but then I am not an expert and brew in a semi-solitary environment with very few knowledgeable folks evaluating the end result. 

I asked the question to insure that I would avoid issues. 

You have now helped me evaluate my initial approach and most likely I will avoid the second bag -- seems like a PITA for an event that may never occur. 

Thank you for taking the time to reply with the detail you provided. 


BTW, will using the Beersmith Water tool and the suggested additions drive the water profile (my well water) to the condition of a ph of less than 6.0?

[Oginme]

BTW, will using the Beersmith Water tool and the suggested additions drive the water profile (my well water) to the condition of a ph of less than 6.0?

The water tool will not calculate out the conditions to get to a specific pH.  It does have a correction tool on the mash tab which will allow you to either determine an amount of acid based upon the estimated pH or your understanding of where your mash pH will end up, or as an adjustment to a mash pH reading.  For either case, you can take the predicted pH (yours or the software's) or the measured pH early into the mash and enter it in the 'measured mash pH' section and then select your acid of choice from the drop down menu.  The software will then calculate the amount of acid required to bring the mash to your target pH value (also a user entered field).

As for the other on BIAB, these are my observations.  It does not make any of what you were doing wrong nor does it make those people who do mash capping or separate steeping of specialty grains wrong in what they do.  It is just a different process.

[mr_beer]

My mistake -- I meant the Mash tool.  Thanks for the answer,