Grain absorption with BIAB

Discussion in 'Recipe Editor' started by Brewer #79626, Dec 28, 2017.

  1. Hoppy Ending

    Hoppy Ending New Member

    Joined:
    Dec 4, 2016
    Messages:
    9
    Likes Received:
    1
    Trophy Points:
    3
    Hey Gang,

    Question about how the "grain absorption" setting feature works for BIAB setups. Since any wort lost due to grain absorption is removed from the kettle when the bag is removed, I would expect the OG to change when I change the grain absorption. The default value of 0.5 qt/lb is too high for BIAB. When I lower it, the recommended total mash water decreases (as expected). However, the OG remains the same with the same grain bill. I would expect it to increase.

    Cheers,
    Randy
     
  2. Yooper

    Yooper Administrator
    Staff Member

    Joined:
    Nov 16, 2013
    Messages:
    2,489
    Likes Received:
    1,576
    Trophy Points:
    113
    Gender:
    Female
    Occupation:
    Happily retired
    Location:
    Upper Michigan/Florida
    Why would the OG increase with the same amount of grain due to absorption? It wouldn't, unless I'm misunderstanding the question. The same amount of grain and the same efficiency will still give the same OG.
     
  3. Hoppy Ending

    Hoppy Ending New Member

    Joined:
    Dec 4, 2016
    Messages:
    9
    Likes Received:
    1
    Trophy Points:
    3
    When you change the grain absorption, the "total mash water needed" for a recipe changes. For example, when I reduce the grain absorption from .5 qt/lb to .3 qt/lb my recipe shows a decrease in total mash water needed by around 1 gallon, depending on the amount of grain. Less mash water should equate to a higher gravity.

    Example:

    Let's say I'm brewing a 5 gallon batch with a 1 gallon boil-off. That means I need 6 gallons of wart at the start of the boil.

    If when I pull out the bag, I loose 1 gallon of water due to grain absorption, that means I need to make a 7 gallon mash.

    However, let's say that when I pull out the bag I loose 2 gallons, this would mean that I need to make an 8 gallon mash... and would need more grain to ensure the same gravity.

    This is how I see a relationship between grain absorption and OG when doing BIAB. Not really an issue for a mashtun because you keep sparging until you're at the right volume.
     
  4. Hoppy Ending

    Hoppy Ending New Member

    Joined:
    Dec 4, 2016
    Messages:
    9
    Likes Received:
    1
    Trophy Points:
    3
    I actually have a recipe that shows gravity readings as such:

    Starting Boil Volume: 7.83
    Boil Gravity: 1.057
    OG: 1.081

    This is with a 1 gallon boil-off rate. This does't add up. The gravity after boiling down to 6.83 should be 1.065.

    I believe this might have to do with the OG calculation.

    Thanks
     
  5. jeffpn

    jeffpn Well-Known Member

    Joined:
    Apr 28, 2015
    Messages:
    3,240
    Likes Received:
    1,557
    Trophy Points:
    113
    Like Yooper said, all that matters is the amount of grain used, and the efficiency. At the end of the boil, it doesn’t matter how you got to the volume that you have in the kettle, say 6 gallons. Efficiency and grain bill determines the OG of the post boil wort, nothing else. Whether the grains sucked up a half gallon or gallon, you’ll have the same 6 gallons post boil.
     
  6. Hoppy Ending

    Hoppy Ending New Member

    Joined:
    Dec 4, 2016
    Messages:
    9
    Likes Received:
    1
    Trophy Points:
    3
    I was considering efficiency to be more about how much you extract from the grains, not how much you squeeze/drain the bag. If I were to brew with less mash water and squeeze the bag to get the volume, you would consider that a higher efficiency than if I were to brew with more mash water and pull the bag right out without letting it drain.

    Correct?

    I still don't understand the calculation where OG is 1.081 and Boil Gravity is 1.057 with a 1 gallon boil off.
     
  7. Hoppy Ending

    Hoppy Ending New Member

    Joined:
    Dec 4, 2016
    Messages:
    9
    Likes Received:
    1
    Trophy Points:
    3
    fishysan likes this.

Share This Page

arrow_white