Author Topic: IBU Calculation  (Read 1268 times)

Offline Joe Sr.

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IBU Calculation
« on: May 29, 2014, 10:41:01 AM »
Another post related to my Old Rasputin "clone."

I followed the recipe since I've never brewed this one before. Zymurgy, July/August 2007.

The recipe says 92 IBUs, but Beersmith calcs something like 28.  The warm and uncarbonated sample I had last night did not taste nearly hoppy enough to be close to Old Rasputin.

The recipe calls for 2 oz of Cluster for 60 minutes, 1 oz of Northern Brewer at 2 minutes, and 1 oz of Centennial at 2 minutes.  I've seen a couple other recipes (BYO) that take the Cluster up to nearly 4 oz, but even then I'm not getting 92 IBUs.

I've never been a numbers guy so I don't usually pay all that much attention to IBUs. And I know Beersmith is only a tool.  But what am I missing here?

It's all in the reflexes. - Jack Burton

Offline Steve in TX

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Re: IBU Calculation
« Reply #1 on: May 29, 2014, 10:43:08 AM »
Are you entering the alpha value for the hops? The recipe may have used a higher alpha crop of cluster, but being that far off is odd.

Is this the recipe you used?

http://byo.com/recipes-tag/item/1182-north-coasts-old-rasputin-the-replicator

Offline Joe Sr.

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Re: IBU Calculation
« Reply #2 on: May 29, 2014, 11:37:40 AM »
Yes to entering the AA%.

I actually used a recipe from Zymurgy that is pretty much identical, but all-grain and uses fewer Cluster hops.  I adjusted the recipe only to replace some of the base grain with DME.
It's all in the reflexes. - Jack Burton

Offline Steve in TX

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Re: IBU Calculation
« Reply #3 on: May 29, 2014, 11:40:43 AM »
Sorry, I read it as BYO and not Zymurgy. I will try entering in to my software later tonight. May have been a typo in the article.

Offline Joe Sr.

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Re: IBU Calculation
« Reply #4 on: May 29, 2014, 11:42:28 AM »
Sorry, I read it as BYO and not Zymurgy. I will try entering in to my software later tonight. May have been a typo in the article.

I snuck back after the initial post and edited it.  Thought it was BYO, but looked at the recipe after I posted.
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Offline erockrph

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Re: IBU Calculation
« Reply #5 on: May 29, 2014, 12:05:26 PM »
A lot of times these clone recipes just scale the brewery's recipe as-is. If the brewery uses a whirlpool or has something else in their process that would increase their utilization that would lead to some discrepancy compared to the homebrew scale.
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Offline dmtaylor

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Re: IBU Calculation
« Reply #6 on: May 29, 2014, 12:30:38 PM »
I calculate about 58 IBUs for 5 gallons, assuming the Cluster alpha at about 7%, Northern Brewer at 9%, and Centennial at 10.5%.  Here's how I swag it, for 5 gallons -- it's all about memorizing the magic factors at the beginning:

3.6 * oz * AA% = IBUs from bittering additions @60 minutes
1.6 * oz * AA% = IBUs from flavor additions @10-15 minutes
0.6 * oz * AA% = IBUs from aroma additions @5 minutes
Add all these together, then add about another +1.5 to the final total and round everything up.

So I get about 50.5 + 3 + 3 + 1.5 = 58 IBUs.  Nowhere near the 90s, like you said.
Dave

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Offline Joe Sr.

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Re: IBU Calculation
« Reply #7 on: May 29, 2014, 12:34:32 PM »
Right, so something must be off.

Beersmith might have been giving me 48 (not 28) but I'm going off memory and I was staring at it after the Hawks won in double OT last night.
It's all in the reflexes. - Jack Burton

Offline HoosierBrew

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Re: IBU Calculation
« Reply #8 on: May 29, 2014, 02:17:38 PM »
A lot of times these clone recipes just scale the brewery's recipe as-is. If the brewery uses a whirlpool or has something else in their process that would increase their utilization that would lead to some discrepancy compared to the homebrew scale.

+1.  I've noticed it a lot. What I do with clones where the IBUs obviously include a lot of whirpool hopping (because the numbers don't add up in software) is to take the given IBU number, add the amount of late hops I think I need to emulate the beer, and add the balance of the needed IBUs in the bittering addition. It comes out closer to the intended than trying to second guess whirlpooling amounts and methods.
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Offline santoch

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Re: IBU Calculation
« Reply #9 on: June 03, 2014, 08:41:48 PM »
May be a dumb question, but are you properly taking batch size into account?  48 sounds pretty close to half the ibus (then with a Rager gravity adjustment).  Did you plug 5 gallons worth of hops into a 10 gallon recipe?
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Offline Kinetic

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Re: IBU Calculation
« Reply #10 on: June 04, 2014, 08:02:47 AM »
The brewery says Old Rasputin is 75ibu.  They probably whirlpool above 190F for 60 minutes after flameout which extracts more ibu than you calculated.  If you don't want to whirlpool for an hour, you can add more hops to get closer 75ibu and start chilling at flameout.  Ibu are still accumulating after flameout depending on the rate of your method of chilling.

Offline Joe Sr.

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Re: IBU Calculation
« Reply #11 on: June 04, 2014, 09:28:33 AM »
May be a dumb question, but are you properly taking batch size into account?  48 sounds pretty close to half the ibus (then with a Rager gravity adjustment).  Did you plug 5 gallons worth of hops into a 10 gallon recipe?

No.  I'm working with a 5 gallon recipe.  I checked that and a number of other settings prior to posting.
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Offline Kinetic

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Re: IBU Calculation
« Reply #12 on: June 04, 2014, 10:32:04 AM »
using Beersmith

2oz cluster @ 60 = 44.9ibu
1oz NB @ 2 = 2.4ibu
1oz centennial @ 2= 2.4ibu

total = 49.7ibu with a 5 gallon batch

If you used 3.25oz of cluster like the BYO recipe, the total ibu is 77.8

The BYO recipe only gives me an OG of 1.074 using extract and steeped grains, but they say it's supposed to be 1.090. 

Offline Joe Sr.

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Re: IBU Calculation
« Reply #13 on: June 04, 2014, 11:00:14 AM »
Thanks.  This is all pretty much confirming that there's something goofy in the recipe and not necessarily with me.

I'm inclined not to mess with it, since it's already fermented and kegged.  If I brew it again, I'll make adjustments.
It's all in the reflexes. - Jack Burton

Offline philm63

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Re: IBU Calculation
« Reply #14 on: June 05, 2014, 04:45:42 PM »
Just a thought; is the recipe possibly using Rager? Is your Beersmith profile set to Tinseth?
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