IBU Estimates - Kettle vs Fermenter approach

Discussion in 'Recipe Editor' started by eheeke, Jan 10, 2020.

  1. eheeke

    eheeke Member

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    There've been a number of discussions on hop utilization in recent months, and I think there are some things in the works. I want to take this opportunity to illustrate a difference I've run into on a recipe and ask for guidance on which estimates are closer to reality.

    I have an IPA recipe with the following key parameters:
    * Preboil: 7.5 gallons
    * Kettle volume: 6.5 gallons (1 gallon of evaporation loss over a 60 minute boil)
    * Fermenter volume: 5.0 gallons (due to leaving 1.5 gallons of hop sludge / trub in the kettle)
    * OG target: 1.060
    * FG predicted: 1.013
    * ABV predicted: 6.09%
    * 60 minute boil with various hop additions

    I have the same recipe loaded using 2 approaches:
    * Kettle volume target of 6.5 gallons @ 80% kettle efficiency
    * Fermenter volume target of 5.0 gallons @ 61.5% brewhouse efficiency (= 80% x 5.0 / 6.5)

    The OG, FG, and ABV are consistent for both scenarios.

    My issue is that the predicted IBUs are significantly different:
    * Kettle approach: 72.23 IBUs
    * Fermenter approach: 104.55 IBUs

    I'm guessing the 72 IBU value is closer to reality. The program still does not seem to handle the kettle losses properly even when loaded in the Equipment Profile.

    For what it's worth, when I view the same recipes on the beta site, I get slightly different values for the Fermenter approach, but the Kettle approach is the same. I'm not sure what improvements are on the beta site at this time.
    * Kettle approach: 72.23 IBUs (same as above)
    * Fermenter approach: 93.92 IBUs

    Here are my two recipes if you want to check them out.
    https://www.brewersfriend.com/homebrew/recipe/edit/832951
    https://www.brewersfriend.com/homebrew/recipe/edit/932254

    I would appreciate any direction you can provide. Thanks.
     
    Pricelessbrewing likes this.
  2. Pricelessbrewing

    Pricelessbrewing QA Software Tester
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    I don't believe any changes regarding IBU are currently on beta, the only thing that should be affecting this is the update coming for improve boil gravity calculations which will affect hop utilization.

    The standalone IBU calculator matches the lower IBU value from target: Kettle.

    I can't open those recipes as they're private, but yooper can take a look if needed. I confirmed in several recipes for the same scenario.

    Yes we never *really* know what the true IBU is, due to variations in hop AA, degredation due to storage, we don't really understand the relationship with IBU and hop solubility or soft limits of a maximum IBU but still ...

    I'm submitting a ticket to get all of the formulas to be aligned. I hope we can make this a priority, but I'll ping you and post in this thread when the update is available on beta, and again when it goes live.
     
  3. Pricelessbrewing

    Pricelessbrewing QA Software Tester
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    It appears the error is that volume differences between postboil, and batch size when using target fermenter is being treated as a concentration of IBU, when it should be a separation of wort and the IBU should not change. Just like the gravity should not change.
     
  4. eheeke

    eheeke Member

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  5. Pricelessbrewing

    Pricelessbrewing QA Software Tester
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    Hey @eheeke, they're still showing as private recipes for me, but I'm confident about what's causing the issue.
     
  6. eheeke

    eheeke Member

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    The recipes are both marked shared/public on my BF recipe list. Maybe the links I provided are from before I made them shared.
    If you have time, please perform a recipe search in BF for Trickster. Mine are “Trickster AG Fermenter” and “Trickster AG Kettle”.
    Sorry about the difficulty. Thanks.
     
  7. Pricelessbrewing

    Pricelessbrewing QA Software Tester
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