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BeerSmith Software => BeerSmith 2 Questions => Topic started by: eddiek85 on March 22, 2017, 10:18:14 PM

Title: Is the estimated IBU in Beersmith pre or post fermentation?
Post by: eddiek85 on March 22, 2017, 10:18:14 PM
Just wondering because all of my recipes seem to have an IBU that is usually higher despite following the recipes. Thanks for any help!
Title: Re: Is the estimated IBU in Beersmith pre or post fermentation?
Post by: Oginme on March 23, 2017, 05:33:25 AM
As far as I have been able to determine based upon reading up on all the models, the IBU number is pre-fermentation. 
Title: Re: Is the estimated IBU in Beersmith pre or post fermentation?
Post by: brewfun on March 23, 2017, 11:01:08 AM
As far as I have been able to determine based upon reading up on all the models, the IBU number is pre-fermentation.

^^^ This is correct. To be a bit pedantic, it is a measurement immediately post boil as some isomers may get trapped in cold break or oxidized out of existence on the way to the fermenter.

Garetz is the only calculation that attempted to predict post fermentation results, which is why it's consistently lower than the others. It's explained in his Hops book, which is out of print, but comes up in the used book market. His hypothesis is a little outdated because it was created assuming bitterness was the product of the boil, not steep or whirlpool times.

Most breweries report that without adding isomers post fermentation, about half of IBUs can be lost in fermentation of most beer styles. Even super saturated IPA's tend to land at 70 to 80 IBUs after fermentation. A lot of this is because an IBU is a rather specific measurement, which doesn't take into account perceptive variations based on hop alpha acid type. Most of us who brew have come across a smoothly bittered 70 IBU beer and another with lingering, resinous coarseness at 45 IBU. Even an entirely unhopped beer can register 2 to 5 IBU because of grain tannins.