Author Topic: IBU Descrepency  (Read 16708 times)

Offline gruversm

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IBU Descrepency
« on: December 07, 2008, 09:43:41 AM »
I understand that I can change the way BrewSmith measures IBU (i.e. Rager, Tinesth, etc...).

My problem is when I try to add recipes (i.e.  "Brewing Classic Styles") from the Zainasheff/Palmer book into BrewSmith, the IBUs never match up. 

What gives?

Offline BeerSmith

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Re: IBU Descrepency
« Reply #1 on: December 07, 2008, 11:17:18 AM »
Hi,
  Many books and magazines use other IBU estimating methods that are not as complex as Rager, Tinseth, etc.  I could not find a quick reference to how they calculate IBUs in "Brewing classic styles" but likely they use another method.

Cheers,
Brad
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jamilz

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Re: IBU Descrepency
« Reply #2 on: December 08, 2008, 02:17:48 AM »
Page 39 to 42 in the book. The section titled, Brewing These Recipes.

The IBUs are calculated using Rager, assuming hop pellets. The volume at the end of the boil is 6 US gallons. All of this and more is in the book.

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Re: IBU Descrepency
« Reply #3 on: December 08, 2008, 09:30:48 AM »
Thanks Jamil!
  Good to see you online!

Brad
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Offline stadelman

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Re: IBU Descrepency
« Reply #4 on: December 08, 2008, 10:40:40 AM »
I am planning to do a Dogfish Head 60 Minute IPA Clone.  I have entered the recipe given in Extreme Brewing into Beer Smith and I get around 45 IBUs, but the recipe calls for 60 IBUs.

Here's my original post-
http://thebrewingnetwork.com/forum/viewtopic.php?f=2&t=11955&start=0

I understand there can be a discrepency becaus of the AA rating for the hops, but a 25% difference seems like too much.

This thread makes me wonder if Beer smith is calculating IBUs correct.

Is it?

Thanks!

Offline BeerSmith

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Re: IBU Descrepency
« Reply #5 on: December 08, 2008, 12:08:54 PM »
Well,
  I know the Rager equations are correct, they have been verified many times.  I note that your recipe cites adding the hops over time rather than at a single point.  This might account for the difference.  I also know that boil gravity makes a difference - so small equipment settings can matter here.

 Jamil - perhaps you can clarify?

Brad
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Offline MaltLicker

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Re: IBU Descrepency
« Reply #6 on: December 08, 2008, 12:20:12 PM »
The different hops utilization models such as Tinseth, Rager, Garetz, etc., all use a different mathmatical algorithm to reach their estimate of the IBUs you'll get from X hops with Y AA% boiled for Z time.  There is a podcast somewhere online (basic brewing radio?) where they entered six different recipes and used various hops model for each recipe.  They got wildly different IBU forecasts (one from each model), and then sent the actual beer to a lab and measured the real IBUs achieved. 

The results were humorous.  No model was clearly the best.  Some were better estimating IBUs with lots of late additions, other were better with low-gravity recipes, etc.  Some estimates were off by ~40 IBUs! 

Two things that may help:  ProMash defaults to Rager, BeerSmith defaults to Tinseth, so if you're using a recipe that someone wrote in ProMash it might be Rager's model.  Second, book and magazine recipes rarely state which hops model they used, so try switching models in BeerSmith and see if any of the main three models gets much closer to the printed recipe.  (Tools\Options\Bitterness)

I actually asked Jamil about this a while ago and he recommend picking one model and sticking to it.  It's all relative, so if you use Rager and 45 IBUs is not bitter enough, increase the hops until you find the taste you seek. 

Offline stadelman

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Re: IBU Descrepency
« Reply #7 on: December 08, 2008, 02:20:42 PM »
I get 44.2 with Tinseth, 53 with Rager and 31 with Garetz.

What do I believe? 

Right now I'm planning to split it down the middle, add 8 or so extra IBUs by adding some more Warrior at 60 minutes.

Any suggestions would be welcomed.

I'm also going to listen to the Basic Brewing podcasts on bitterness.  I found a three of them.
http://www.basicbrewing.com/radio/mp3/bbr01-05-06.mp3
http://media.libsyn.com/media/basicbrewing/bbr03-20-08ibu.mp3
http://media.libsyn.com/media/basicbrewing/bbr07-05-07ibutest.mp3

Offline MaltLicker

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Re: IBU Descrepency
« Reply #8 on: December 08, 2008, 02:42:50 PM »
I just played with an APA recipe and toggled between Rager and Tinseth.  If I recall it correctly, Rager gave no increase in IBUs past 60 minutes, whereas Tinseth did increase slightly. 

Rager, however, gave slightly larger increases in IBUs as I increased the hops at five and two minutes, whereas Tinseth forecast less IBUs from such late additions. 

The extra Warrior at 60 minutes would likely be forecast similarly; it is the extremes in time (past 60) and quantity (high late additions) that create some variance in the models.  It is somewhat similar to asking economists to forecast GNP using the same set of data.  No two estimates would be the same. 

D.ErynC

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IBU Descrepency
« Reply #9 on: October 29, 2009, 03:28:53 AM »
Something to keep in mind concerning IBU numbers is that the number can vary greatly depending on which formula was used to calculate it. There are no fewer than six formulae and their results vary quite a bit. So a brewer needs to do a little experimentation and pick one that matches his perception of the bitterness he perceives in his brew and stick with it. The only way to know for sure the bitterness for a given beer is to have it analyzed in a lab.

Offline zgoda

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Re: IBU Descrepency
« Reply #10 on: October 13, 2010, 03:44:24 AM »
In reality, not many people are able to note a difference of 5 IBU unless it crosses their borders between "bitter" and "very bitter" (mine is around 50 IBU).

Other factor is correct calculation of brewhouse efficiency. Most recipes found on the 'net takes unknown assumption on efficiency, was it 75% expected or 80%? And how it was calculated (absolute efficiency or relative - in Europe we calculate absolute efficiency, in U.S. relative is used)? With higher efficiency you get the same IBU (assuming you get the same 20L of wort) but the wort has higher gravity and the bitterness is not prominent in taste.