Author Topic: IBU question  (Read 3080 times)

Offline hegeyb

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IBU question
« on: March 05, 2011, 09:20:47 PM »
I brewed a clone beer today but before i started I worked on the recipe and either the recipe is wrong as written or beer smith is calculating it wrong (I don't think so) or I am missing something.  I am using the recipe from the BYO 250 classic clone recipes magazine for Terrapin Rye Pale Ale clone.

It states:
magnum: 1 oz 14 AAU 60 mins
Fuggle:  .75 oz 3.75 AAU 30 mins
East Kent: .5 oz 2.38 AAU 20 mins
                .5 oz 2.38 AAU 10 mins
Cascade:  1 oz 6.8 AAU 3 mins

total IBU: 45

So I assume it is including the Amarillo dry hop 16.4 AAU in the total.  When I enter this recipe into beer smith, I get a total IBU of 59.8  with very different ibu's.

When I enter this info into beer smith I get:
Magnum 42.7 IBU
Fuggles 7.9
East Kent 20 mins 4.4
East Kent 10 mins 2.7
Cascade 2
Amarillo 0 dry hop

Why are the numbers so different?  Am I missing something or is the recipe in the magazine wrong?
I decreased the magnum to .65oz and ended up with the 45 IBU total the recipe called for.  Was the the right thing to do?  That allowed me to keep the IBU within the range for the beer style.

Thanks!! ???

Offline MaltLicker

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Re: IBU question
« Reply #1 on: March 06, 2011, 09:41:49 AM »
To compare exactly, you'd have to know which IBU utilization model the book used.  BeerSmith defaults to Tinseth.  There are slight adjustments for other variables such as leaf/hop/FWH/mash hops, etc.

Using my same equipment profile, I just found an 18 point difference between Rager and Tinseth in a robust porter recipe.  And neither of those is "correct" but merely estimates based on these guys "models." 

And some equipment and water volume settings can affect utilization, adding more variance to a book/magazine recipe if you don't know all their settings. 

Offline 88Q

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Re: IBU question
« Reply #2 on: March 06, 2011, 10:02:43 AM »
And to take it a step further.... you have to ASSURE that the ACTUAL AA% of the hops you actually use is the same as the ones in the recipe if you want the exact same result numbers...... In other words, the Magnum (for instance) may have used a lower or higher AA% crop (differing from year to year - region to region) than the Magnum's numbers in BeerSmith. So if you want th clone to be the same, you need to manipulate the amount of hops based on the actual AA of your batch within BeerSmith....

Hope this make sense. Didn't sleep last night!