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 scinerd3000 05-18-2009 03:46 PM

Promash Far wrong! for IBU calculations

I'm getting ready to brew Brewpastors Stoneface RIS and it calls for a bunch of warrior hops and and the ibu numbers im calculating when i changed the recipe around don't make any sense. Acording to tinseth using this websites calculation How to Brew - By John Palmer - Hop Bittering Calculations by hand im coming up with completly different numbers. The wort is 1.100 SG with 5.5 gallon volume and 2 oz of warrior hops at 60 minutes. Promash using rager and tinsith are both above 120 ibU. Rager is 138!!!! When i calculate by hand im getting around 73.6. WTF is going on.

 ajf 05-19-2009 02:51 AM

I think that you have made a mistake in your calculations somewhere.
The original recipe is 10g and uses 10 oz hops. You've scaled it down to 5.5g which should require about 5.5 oz hops, but you've only got 2 oz.
Using my home brewed Tinseth calculator, assuming the hops are 15% AA, and you boil down from 6.5g to 5.5g to get an OG of 1.100. it shows 64 IBUs using 2 oz hops, or 178 IBUs using 5.5 oz.

-a.

 david_42 05-19-2009 01:51 PM

Bittering is a non-linear process. All of the calculators are approximations. They make different assumptions and none of them take into consideration the saturation of the wort. Any time you get a result over 100 IBU, it is wrong.

http://www.homebrewtalk.com/gallery/.../hop_util1.png

 scinerd3000 05-19-2009 06:07 PM

my hops are 18.4%. i was going to go for a single hop addition instead of the multiple like brewpastor had but when i calculate the ibu's they are different depending on how i calculate. I did scale down to 5.5 gallon with only 2 oz hop at 60 minutes...The issue is I'm geting anywhere from 65-140 with the same variables through either promash or other searches online. It just didn't make any sense.

david42- thanks, i never thought about saturation. good point and i really like the graph

A weakness in Promash is the hop utilization factor does not appear to be adjusted with changes in OG, you will have to tweak it by hand for high OG batches.

 ajf 05-20-2009 02:59 AM

Sorry, I based my previous comments on the Dark Night of the Soul recipe.
Based on Stoneface with 18.4% AA hops, I calculate 2 oz of 18.4% AA to give 78 IBU, and Promash/Tinseth gives me 90 IBU.
I don't see anything approaching 120 IBU.

-a.

 scinerd3000 05-20-2009 04:16 AM

Quote:
 Originally Posted by ajf (Post 1334437) Sorry, I based my previous comments on the Dark Night of the Soul recipe. Based on Stoneface with 18.4% AA hops, I calculate 2 oz of 18.4% AA to give 78 IBU, and Promash/Tinseth gives me 90 IBU. I don't see anything approaching 120 IBU. -a.
using rager im at about 132....wierd. i still dont know why its so damn high...im betting klad is right and promash just doesnt change utilization numbers for higher gravity...its the only thing that i can think fits.