bug? IBU changes with pre-boil

Discussion in 'Recipe Editor' started by Hobbes, Feb 16, 2019.

  1. Hobbes

    Hobbes Member

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    I noticed if you change your preboil volume the IBU calcs go up/down... if i enter "0" for preboil volume i get 399,654.96 IBU. I tried to think of how logically the pre-boil volume would affect the IBU... perhaps having more wate beforehand and boiling harder causes more IBU to be extracted.

    I'm not sure that's right... i think once you have "enough" water in the kettle that it's probably just a function of temp (boiling vs whirlpool) and time. I could see if it was a soupy mess and not enough water to effectively extra IBUs, but adding more and more water (200g, 2000g) seems to keep raising IBU.
     
  2. BOB357

    BOB357 Well-Known Member

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    Adding a given amount of the same hop to different pre-boil volumes of the same wort would produce different concentrations of bittering compounds, with the greater concentration being in the wort of lesser volume. In practical brewing applications this would translate out to more IBUs in the post-boil of lesser volume, assuming that the only adjustment you made was to the pre-boil volume.

    When you say, "once you have enough water in the kettle", are we to assume that you're not planning to boil the hops in wort, or that you're changing the pre-boil volume by diluting wort? While time and temperature are primary factors in the Isomerization of Alpha Acids, the concentration level of your wort must also be factored in. Also, most software is written to work within reasonable parameters, so looking at some of the numbers in your post ,it may very likely be further complicating the results you're seeing.






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  3. Hobbes

    Hobbes Member

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    I went and dbl checked the IBU formulat, it does in fact account for volume... i guess i'm just suprised that I see the IBU chagne from 60 to 64 when toggling between 7g and 8g preboil sizes.

    Then.. i'm almost certain there is a bug regarding post-boil size. If I change from target fermenter to "kettle" it doesn't change IBU all... my kettle losses are 1g. So I change kettle to "6.5" to account for wanting to end up with 5.5 into the fermenter then IBU changes to 51 IBU. I would expect the software to have known that when we were talking "target fermenter" we were talking about a 6.5 kettle volume because of my 1g losses in the equipment.

    Maybe we should remove the "target fermenter" completely if we can't use the equipment losses? Really the only way I can seem to get these recipes to line up with the other 2x software i'm using is to design them first elsewhere and import them.
     
  4. Yooper

    Yooper Administrator
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    Volume plays a huge part in the isomerization of alpha acids and the amount of IBUs- so I'm not sure what the issue is. Some people target end of kettle, and pour all into the fermenter, while others target the fermenter volume and actually toss a lot of wort/trub if they don't whirlpool first. I'm not sure how we could change it to make sense to all, if we changed the "target fermenter" option. I guess I don't understand the issue here, because I'm trying to picture what you mean.
     
  5. Nosybear

    Nosybear Well-Known Member

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    Yooper, I got this one: The preboil volume is affecting the boil gravity (all other things being held constant). The utilization equations use wort gravity, not volume, as a factor so if you up the volume, you reduce the gravity, which increases utilization. Likewise, if you reduce the preboil volume, you increase the boil gravity which decreases utilization. The role of the volume is to determine the preboil gravity. It isn't a bug in the software, it's the equations doing what they should.
     
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  6. Hobbes

    Hobbes Member

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    Also, regarding target; it's fine to have "fermenter" vs "kettle" but that input should toggle something. This may be long winded explanation, but switching this toggle should change something... somewhere. It appears to me the volumes in equipment profile are not being used yet.

    I see it you have currently two options:
    1) if you pick target "kettle" then any "kettle losses" in your equipment profile are not taken into account, as you probably do this yourself or have none... eg, you either dump it all in or you know you need to get an extra gallon due to losses (brew to 6.5g in kettle so you have 5.5 into ferment and finally 5g into keg after ferm losses). This could be default, as most beginners do not worry about small losses or are dumping everything in.

    2) if you pick target "fermenter" then there is a "post-boil" number that isn't being displayed here that matters. "target fermenter" with 5.5g means i want 5.5 into the fermenter when done (i assume). That should mean post-boil is going to be "fermenter vol + kettle losses" and pre-boil should be post-boil + evap rate. Eg, if i want 5.5g in fermenter and i have 1g of kettle/hose loss then post-boil is 6.5 and with 1.5g evap rate over a 60 min boil i should have 8g pre-boil. It should all work with equipment profile numbers to help me figure out what pre-boil i need, and what post-boil i'm shooting for (checking halfway through boil to adjust rate if i'm too fast/slow).

    Maybe this would all be easier to convey to users if you listed pre-boil, post-boil, and target fermenter volumes all separately. You could enable vs gray out options depending on what they want to target towards. Currently "post-boil" isn't really represented, but instead a toggle of "target". Users that dump their kettle directly into fermenter would have "0" losses, but other uses have upwards of a gallon due to whirlpooling/sidepickup + hoses + chiller deadspace.

    But, switching between target "fermenter" an "kettle" without changing the volume should change the IBU.

    Real world example:
    My system 5.5g fermenter, 1g losses between kettle (side pickup/whirlpooling) + hoses + CFC chiller
    boil off rate 1.5g/hr, 60 min boil
    If i want 5g batch then i target 5.5 into fermenter (.5g ferm losses), and i target 6.5 ending/post boil, and i target 8.5 pre-boil

    For 10g (two kegs) i target 11g fermenter (two 5.5g fermenter), and i target 12g post-boil and 13.5g pre-boil.

    So if i pick 6.5 "kettle" target and switch to target "fermenter" it should now assume the "6.5" really means 7.5 post-boil which would change IBU/OG/etc. Or it should adjust 6.5 to "5.5" because it knows my equipment profile was accounting for 1g of losses. Or someone just has to know the reason the OG/IBU changed is due to the volume differences and know that they have to adjust volumes to get back to their recipe OG/IBU targets.
     
  7. Hobbes

    Hobbes Member

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    Yeah, i dbl checked the actual equations... and the IBU is affected by volume/gravity; i just never really thought it would be by so much. On an IPA i was adjusted it was going up/down by 4-5 IBU. Seemed like a lot.... i guess it's relative.

    Switching target though, i'm realllly surprised that changes nothing.
     
  8. Nosybear

    Nosybear Well-Known Member

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    Switching target doesn't change anything on volumes, really. It's kind of a fiction based on your preference. If your batch size is 5 gallons, it takes the same amount of water whether you target the fermentor (5 gallons after all losses in the process) or the kettle (about 6 gallons, not counting boil off, trub and hop loss). Fermentor has always made more sense because that's the actual batch size I want,
     
  9. Hobbes

    Hobbes Member

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    Fermenter makes perfect sense, maybe the confusion is that there is no preboil volume display. Also, toggling these values should be changing more than just IBU. The value you can enter just says "boil vol". I took this to mean "pre boil vol" because it's affecting the IBU and nothing else.

    I don't think this is 100% correct though, we can confirm by looking at the brew session info. I went and grabbed a 5g recipe and saved it as "TEST", changed target to fermenter, batch to 5, preboil to 8.5, equipment "default" which is my setup listing 1.5g/hr evap, 1gal losses in kettle, and 1/2g "misc" losses
    1) adding log entry for "preboil gravity" suggest we should have 8.15g... i'm not sure where this math comes from. I can't arrive at 8.15 any way i shape it up. My boil off rate is 1.5, my losses are all in even 1/2g amounts.
    2) adding log entry for "boil complete" suggest i should have now 6.65, this make sense with the boil off rate of 1.5, if we assume the 8.15 preboil is correct
    3) brew day complete has no suggested value, but list "Fermenter" volume for me to fill out.. this tells me that the "boil complete" volume is not in fact the fermenter volume, and later we input packaged volume so i would assume fermenter volume is actually kept seperate. If you go to recipe editor and put "100%" for eff and read the OG, then come here and put the OG and batch size you get 100%. I would expect that the brewhouse eff would be calculated based on the "packaged volume" as there is potential here to lose more beer.
    4) inputting a value for packaged volume like "10000g" does not change total brewhouse eff, which leads me to believe brewhouse eff is calc as if "fermenter volume" is packaged volume, which leads to some assumptions in recipe generation where I assume "fermenter volume" is "batch size"... because it is here that we decided brewhouse efficiency and we're using "Fermenter volume" as the total batch size. Any number lower than your recipe batch size will cause you to suffer.


    If i change target from "fermenter" to kettle then my preboil vol goes to 6.5 and my boil complete goes to 5. I would hazard a guess that what I want todo here is use "kettle" target but put the 5.5 i want into my fermenter there... because my post-boil should be 6.5. So let me put 5.5 for "batch size" and kettle... now my pre-boil vol is 7g. Where did that come from? Boil complete is no 5.5g. So in "kettle" mode the boil complete is always the batch size, and your preboil will always be batch size + evap rate. It will not use the "boil vol" that you input on the on the sheet.

    IMO, target fermenter is great but also "batch size" is good... but i need to know what they mean.
    1) I have 1/2gallon of "fermenter losses" calculated in, so i target "5.5g into the fermenter" so i can transfer 5 whole gallons into the keg.
    2) So, 5.5 into the fermenter means on my system i need 6.5 in the kettle because 1 whole gallon is lost (up to) when i transfer due to using a side-diptube, CFC chiller, and some tubing losses.
    3) so 6.5 ending "post boil" is what I need hwen transfering so i need to know what pre-boil would be, adding in 1.5g for 60 min boil or 2.25g for a 90 min boil gets me 8g or 8.75g depending if we're doing 60 or 90 min boil

    So if batch size is the actual ending batch size then we are missing an important key element in recipe development and that is the post-boil volume.

    The pre-boil and post-boil volumes should be calculated for you based on losses and the target batch volume. If these are user editable then the batch size should calculated based on user-supplied values. Eg, if i manually put pre-boil volume of 20gallons, then my batch size is now 20-(boil-off)-(kettle-losses).

    To summarize... i'm changing values here that should be interdependent and they are not tied together. This is fine for simple recipes where user knows his volumes and is generally brewing with the same profile. But i'm looking to see what happens when I scale a recipe from 5g to 10g, or if I increase my mash eff, or what if I want to do a hazy IPA with a lot of hops that will affect my packaged volume.

    Eg, If i'm doing a new hazyboi and want to dump a lbs of hops in there but still want a full 5g keg then how much grain do i need, sparge water, preboil vol, fermenter volume, etc... all to get to the same batch size of 5g when the whirlpool hops and dry hops are going to be soaking up an extra 10%. If we tie these values together in the calculator and make "boil vol" a calculated number it helps me design the recipe.

    Flipside, if someone wants to know how much product/batchsize they will get from a 8.5g pre-boil and their equipment then maybe that's a way to go too... i just have never taken that approach. The current editor seems to support neither, and "boil vol" is a freetext field.
     
  10. Hobbes

    Hobbes Member

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    we should prob just close this one.. the original post was regarding a bug i thought i found with IBU. Turns out the behavior was as expected in that IBU does change with preboil volume.

    My resulting confusion as to if "boil vol" is preboil vol is not related... and the resulting inconsistencies in recipe design should warrant another ticket if anyone wants to investigate.

    If this is operating as intended I can move on. I would hate to tie some of these values together that results in normal happy brewers of 5g batches getting crazy values all of the sudden due to wierd/incomplete equipment profile setups.
     

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