Conversion vs. "pre-boil" efficiency for BIAB

Discussion in 'Brew Sessions' started by JimFisher, May 1, 2018.

  1. JimFisher

    JimFisher New Member

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    How are you BIAB people measuring "conversion" versus "pre-boil" gravity for BIAB? I've been using BF for a couple of years and have always pulled the bag, squeeze, then enter the same number for my conversion and pre-boil gravity. A "eureka" moment caused me to ponder the fact that I've been doing it wrong this whole time.

    I NOW assume that, for conversion efficiency, I should take a reading at the end of the mash before I take the bag out, then another reading after I squeeze for pre-boil.

    Am I correct or no?
     
  2. jeffpn

    jeffpn Well-Known Member

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    I BIAB, and I gave up on readings until my wort is in the fermenter. It took me a few brews to get it dialed in, but I’m usually pretty close on points. I set my recipes for 70% brew house (I think it’s called).
     
  3. JimFisher

    JimFisher New Member

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    I guess I answered my own question. According to the BF website, the "conversion" and "pre-boil" are, in fact, the same reading for BIAB people. I was getting blasted on a Facebook page for stating that they were the same reading. I win. ;)

    1) Conversion Efficiency: The percentage of total available sugars that were extracted from the grains inside the mash tun.
    • Brew Log Type - 'Mash Complete'.
    • Measurement Option A - first runnings:
      • Gravity - sample taken from first runnings.
      • Volume - strike water used (count all water added to the MLT before the sample was taken).
      • Generally, only accurate for recirculated mash systems.
    • Measurement Option B - blend of runnings:
      • Gravity - sample taken before the boil, blend of all runnings.
      • Volume - how much water went into the MLT, counting strike and sparge water.
      • Note: With Option B, the wort sample must be fully blended from all the runnings to be accurate. First runnings have a higher gravity than second runnings.
      • Best option for batch spargers. Works for BIAB and partial mash (MLT and kettle are the same).


        https://www.brewersfriend.com/faq/#brewsessions5
     
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  4. Trialben

    Trialben Well-Known Member

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    yep thats what i do. i take my coversion and pre-boil gravity after sparge giving the kettle a good stir to try and mix up all the wort before running a couple of liters into jug and dumping it back a few times before i pinch my sample.
     
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  5. Hawkbox

    Hawkbox Well-Known Member

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    I have no idea how the conversion works and end up >100% most of the time so I just do the pre-boil now and post boil but only really care about the post boil.
     
  6. KC

    KC Active Member

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    Either your volume is wrong, the PPG of your malt is wrong, or you're including other sugar additions.
     
  7. Trialben

    Trialben Well-Known Member

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    ive got over 100% before too.
    so if i understand it correctly and if not let me know please is.

    conversion efficiency is total volume of brew liquor including mash and sparge volume.

    preboil is as above minus grain absorption. so the gravity reading before boil begins.

    i usually find ending kettle/ into fermentor gravities more trustworthy. but i get an idea where im at given my preboil as you know you going to get X amount of gravity points off your 60min boil.
     
  8. JimFisher

    JimFisher New Member

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    Trailben,

    I think you're technically correct, but in the end, it's still the same reading. Again, according to BF website:

    1) Conversion Efficiency: The percentage of total available sugars that were extracted from the grains inside the mash tun.
    • Measurement Option B - blend of runnings:
      • Gravity - sample taken before the boil, blend of all runnings.
      • Best option for batch spargers. Works for BIAB and partial mash (MLT and kettle are the same).

    2) Pre-Boil Efficiency: The percentage of total available sugars that made it into the kettle.
    • Gravity - measured before the boil, blend of all runnings.
     
  9. KC

    KC Active Member

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    https://www.brewersfriend.com/2012/11/30/making-sense-of-efficiency-definitions/

    The calculations aren't presented clearly and I've been doing it incorrectly myself. The difference for BIAB is the volume amount you enter in the logs.

    Conversion Efficiency:
    Mash Complete Volume: total water added to the mash
    It doesn't matter if the bag is in or out

    Preboil Efficiency:
    Preboil Volume: Amount of liquid remaining in the kettle
    Bag is out and squeezed (if you squeeze it)
    It doesn't matter if you top off the kettle with more water
     
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  10. Trialben

    Trialben Well-Known Member

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    ♤♤♤ thats how i record em KC.
     
  11. Hawkbox

    Hawkbox Well-Known Member

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    That is what I've been doing and I still get greater than 100% at times. I added X amount of water, got Y gravity. I'm not sure how I can screw this up.
     
  12. KC

    KC Active Member

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    My system has a basket and the gravity inside the basket is much higher than outside the basket. That throws off the readings.
     
  13. Head First

    Head First Well-Known Member

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    When i first started using BF I struggled with the efficiency calculator and found even the slightest mismeasurement causes changes in efficiency. Think about reading a hydrometer, 1 point makes a difference in the outcome. A half cup off in liquid makes a difference. RDWHAHB
     
  14. KC

    KC Active Member

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    And the default malt settings are only an estimate. Spec. efficiency varies heavily across malts. It is highly influenced by the grind and by moisture content.

    e.g. the default American 2-row is listed as 37ppg. If you have a malt with a CG spec of 83%, and/or your mill works really well, and/or your malt batch is dryer than the test batch, you can get over 100%. That's a problem with the recipe setup.
     
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