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Brewing Topics => Brewing Discussion => Topic started by: jmelgin on January 09, 2019, 01:27:43 PM

Title: IBU Estimate Doesn't Look Right
Post by: jmelgin on January 09, 2019, 01:27:43 PM
I'm developing a recipe for an imperial chocolate stout (trying to come up with an Abraxus clone).  The recipe I'm working with came out of Craft Beer & Brewing magazine and was used at WeldWerks in Colorado.  The base recipe has 1.5 oz of Magnum Hops @ 10.5% AA for an IBU of 45.  However, when I put this into BS3, I get an IBU estimate of 24.7.  If I go back to BS2, I get 43.1.  I'm at 8200' elevation which is programmed into my equipment profile and am using a 90 min boil.

Would you expect the impact of elevation to reduce the IBU's by this much?  Just want to be sure before I amp things up on this recipe!

Thanks,

Mike
Title: Re: IBU Estimate Doesn't Look Right
Post by: Oginme on January 09, 2019, 01:34:31 PM
short answer:  Yes.

The lowering of boiling temperature due to elevation causes a drop in the isomerization of the alpha acids in the hops.  At your elevation, water boils around 196F, much lower than the 212F at sea level.  Change the elevation back to sea level and it should pop back up to around 43 IBU. 
Title: Re: IBU Estimate Doesn't Look Right
Post by: jmelgin on January 09, 2019, 02:25:25 PM
Understood - thanks!