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Boil length changes IBU's???

Yeasty

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I don't understand why when I change the boil time it affects the IBU totals. I don't mean the pitching times, just the boil length.
Is there a way to make it stop doing that?
 

bonjour

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I don't understand your question because I expect IBU's too change if boil time changes.

First the obvious, if you boil the hops longer, you get more IBUs.  I think you understand this.

Let's add hops at 60 minutes with a 60 minute boil, you get x amout of IBUs
Increase the boil time to 120 minutes but add the hops at 60 minutes, the IBUs should decrease.  Why?
because you have lost something close to a gallon of water due to boiloff/evaporation and the wort is more concentrated than for a 60 minute boil given the same starting volume.

If you increase your boil volume by your expected loss over the additional boil time you should see the same IBUs

Hope this helps

Fred
 

Yeasty

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Sorry Fred, much as I appreciate the response, it doesn't help! ;D
If I have a target OG of 1.055, that's post-boil.
Say I have 12# of grain, whatever.
Now if I boil an ounce of EKG's in there, I should get about 14 IBU or whatever.
Plug that all in to BeerSmith, and then go to the top and increase the boil time, and the IBU's go up.
Bwuhh?!
I still have the same OG (=postboil SG, right?)so why do I get more IBU's?
???
Hope that makes the question clearer.
 

BeerSmith

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Yeasty,
  There is a pretty simple answer: the longer you boil hops, the more alpha oil gets extracted from the little glands in the hops.  Its the boiling process that releases these oils from the hops over time - longer boil=more oils.  The alpha oils provide the majority of the bitterness you perceive when you drink the beer.  The various IBU formulas all take boil time into account for this reason.

  Therefore longer boils result in more alpha oil extracted, which leads to more bitterness, and higher IBU.

Cheers!
Brad
 

bonjour

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Ok yeasty,

in BeerSmith, (because no other program is better  :D )
The boil time is set at 60 minutes (above the ingredients box)
You enter your grain bill (whatever)
You enter 1 oz of hops.  Note that the hops are set for 60 minutes (boil time above)
You note the IBU level of xx IBU's

Now you increase your boil time to say 120 minutes
You should note that the IBU's have NOT changed because the hops are still called to be added with 60 minutes left in the boil.

However, if you increase the boil time on the hops using the controls to the right of the ingredients box the IBUs will go up because you have better utilization by boiling the hops longer
Fred


 

Yeasty

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Right. OK. Great.
Now, why then do my IBU's indeed increase when I increase the boil length (but leave the hop times the same)?
??? ??? ???
Am I the only one with this problem?
Once again, to be perfectly clear - a 120m boil with and ounce of hops at 60m gives MORE IBU's than a 70m boil with same 60m addition.
I must have something set weird in my preferences.
 

Yeasty

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Someone please try this so I don't sound so crazy.
Open any recipe you like, note the IBU's and then go to the boil time field (just to the left of "brewhouse efficiency" - DON'T change the hop boil times!) and adjust it up or down, watching the IBU totals below.
 

BeerSmith

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Yeasty,
  I assume you have the "Set boil volume based on equipment" box checked.  Now as you change the overall boil time you will notice that it is also changing your boil volume.  Now you probably won't be too surprised to hear that the boil volume also affects the IBUs since it is used in the equation for both the pre-boil SG and also the IBU calculation.  Changing the boil time changes the boil size (to compensate for higher boil off), which in turn changes the pre-boil SG and also the IBUs.

  Try it again, but this time with the "Set boil volume based on equipment" turned off, and I think you will find that the IBUs don't change anymore.

  Nobody said this stuff was easy - you should how complex the code is to convert a recipe from all grain to extract while still trying to maintain the correct color, SG and IBU balance for the beer!  Some people think BeerSmith just substitutes the grains, but it actually does a whole lot of rebalancing after the substitution to keep the beer in balance.  In the new version I'm working on I made even more adjustments to try to handle light color beer conversions better.

Cheers!
Brad
 

Yeasty

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OK, cool. Easy enough.
I've said it a million times, but just in case you've forgotten, I LOVE the program. What you've done is amazing.
Now, explain a little further if you would about boil off.
The preferences set what percentage of loss there is in a set amount time, or in a set amount of volume? IOW, when I put in 12%, say, am I telling it that my batches go from 112% to 100 percent in the time it takes me to boil? (In which case it makes perfect sense to have the "set boil volume" capability) or am I telling it 12% per hour?
I guess that's where my confusion is.
But for now, I'll just leave it unchecked (yes, it was checked) until I figure out why I'd need to set the boil volume anyway (<-second question).
Thanks!
 

BeerSmith

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Yeasty,
  An accurate boil volume is needed to get a good IBU calculation.  The boil volume is used to calculate your pre-boil gravity which is used for IBUs.  Higher boil gravity results in less oil being extracted, and lower IBUs.  Lower boil gravity does the opposite, which is why you need a lot more hops in a small boil extract recipe than in a full boil all grain recipe.

  The boil off is percent per hour - so if you set 12% per hour you will lose 12% of your pre-boil volume in an hour.

Cheers!
Brad
 
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