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Help me understand this IBU question

daveozzz

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I have the attached recipe and the IBU calculation is confusing me.. why do the itemised IBU values (21.3) not add up to the total IBU value (49.1)?
This is likely something to do with that fact this is a partial boil and/or the majority of the extract is a late addition.. am I doing something wrong here?
Code:
----
BeerSmith 2 Recipe Printout - http://www.beersmith.com
Recipe: Nelson Sauvin IPA
Brewer: 
Asst Brewer: 
Style: English IPA
TYPE: Extract
Taste: (30.0) 

Recipe Specifications
--------------------------
Boil Size: 4.00 l
Post Boil Volume: 3.47 l
Batch Size (fermenter): 11.00 l   
Bottling Volume: 9.49 l
Estimated OG: 1.062 SG
Estimated Color: 20.6 EBC
Estimated IBU: 49.1 IBUs
Brewhouse Efficiency: 72.00 %
Est Mash Efficiency: 0.0 %
Boil Time: 60 Minutes

Ingredients:
------------
Amt                   Name                                     Type          #        %/IBU         
160.00 g              Caramel/Crystal Malt - 40L (78.8 EBC)    Grain         1        6.6 %         
750.00 g              Pale Liquid Extract (15.8 EBC)           Extract       2        31.1 %        
18.00 g               Nelson Sauvin [12.00 %] - Boil 60.0 min  Hop           3        14.1 IBUs     
1500.00 g             Pale Liquid Extract [Boil for 15 min](15 Extract       4        62.2 %        
18.40 g               Nelson Sauvin [12.00 %] - Boil 15.0 min  Hop           5        7.2 IBUs      
10.00 g               Nelson Sauvin [12.00 %] - Aroma Steep 30 Hop           6        0.0 IBUs      
1.0 pkg               Safale American  (DCL/Fermentis #US-05)  Yeast         7        -             


Mash Schedule: Single Infusion, Light Body, No Mash Out
Total Grain Weight: 2410.00 g
----------------------------

Sparge: Remove grains, and prepare to boil wort
Notes:
------


Created with BeerSmith 2 - http://www.beersmith.com
-------------------------------------------------------------------------------------
 
Hi,
  It is the late extract addition that is throwing this off.  This was a bug in BeerSmith 1.4 that I thought I corrected in BeerSmith 2 - which version are you using?

  The issue is that the total IBUs are being calculated correctly (so the total is right) but the individual hop addition contributions are being calculated without factoring in the late extract addition, so those are off a bit.

Brad
 
Thanks for the info Brad,
I was using 2.0.54 - I just installed 2.0.57 which has the same problem.

So the itemised hop weights are the correct addition sizes to get to the total IBUs listed..? That was mostly what I was worried about since it looked like I may be putting way too little hops in.. that's good to know.
 
Brad,

Maybe I can piggyback on this question because I'm having an issue calculating IBUs as well.
Mind you, I am a BIAB brewer, but found a recipe for Rogue Dead Guy Ale that I want to do. It's extract with steeping grains which I don't normally do, so I'm hoping this is just a setting issue that I can't figure out.

It's meant to be a partial boil so I will include as much info as I can here.

Style: Mailbock/Helles Bock
TYPE: Extract
Taste: (30.0)

Recipe Specifications
--------------------------
Boil Size: 3.00 gal
Post Boil Volume: 2.71 gal
Batch Size (fermenter): 5.00 gal 
Bottling Volume: 4.60 gal
Estimated OG: 1.063 SG
Estimated Color: 10.2 SRM
Estimated IBU: 31.2 IBUs
Brewhouse Efficiency: 72.00 %
Est Mash Efficiency: 0.0 %
Boil Time: 60 Minutes

Ingredients:
------------
Amt                  Name                                    Type          #        %/IBU       
3 lbs 4.8 oz          Pale Liquid Extract [Boil for15 min](8.0 Extract      5        35.5 %       
2 lbs 4.0 oz          Extra Light Dry Extract (3.0 SRM)        Dry Extract  2        24.2 %       
2 lbs 8.0 oz          Munich Liquid Malt (8.0 SRM)            Extract      3        26.9 %       
1 lbs 4.0 oz          Carastan (30.0 SRM)                      Grain        1        13.4 %       
1.60 oz              Perle [7.00 %] - Boil 60.0 min          Hop          4        23.6 IBUs   
1.00 oz              Saaz [4.00 %] - Boil 0.0 min            Hop          7        0.0 IBUs     
1.00 tsp              Irish Moss (Boil 10.0 mins)              Fining        6        -           
0.50 tsp              Yeast Nutrient (Primary 3.0 days)        Other        9        -           
1.0 pkg              Pacman strain (Wyeast 1764 #)            Yeast        8        -           

The directions call for a 30 minute steep of the Carastan. After that:
- Add the light DME and Munich LME + water to get to 3 gallons volume
- Take to boil and add Perle for 60 minutes
- Add remaining light LME for last 15
- Add Saaz @ 0 minutes
- Cool wort, add to fermenter and top off with water to get to 5 gallons.

Now, I don't do partial boils either, so maybe the IBUs get calculated differently because of this?

What setting (equipment, ec.) should I be using? I'll admit I don't know how to set up a profile/recipe for a partial boil.

The recipe targets 40 IBUs, but I only get 31.2.

What am I missing?

I appreciate any help.
Thanks.

FWIW, I'm using 2.0.40
 
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