IBU question

Hey all,
I just got the July/August 2012 issue of Zymurgy and entered the odell IPA clone recipe into the latest version of beer smith.

The magazine says:
OG: 1.066
IBU: 60

Beersmith says:
OG: 1.066
IBU: 33.6

I triple checked my entries and everything is correct. I switched to different equipment profiles and no luck. I don't see how it could be nearly half. I also tried the stone ruination ipa recipe from the same issue and had the same problem. The target IBU is 105 and beer smith says 85.1

Anyone have any ideas?
Mike

EDIT - Well, I figured out that switching the bitterness formula from tinseth to rager fixes the issue with the stone ruination clone, but since there is no hopback option in beer smith it does not fix it for the odell ipa clone although it gets it closer. So, it seems that beer smith defaults to tinseth but these recipes in zymurgy use rager. Any insight to this?

banjofritz said:

EDIT - Well, I figured out that switching the bitterness formula from tinseth to rager fixes the issue with the stone ruination clone, but since there is no hopback option in beer smith it does not fix it for the odell ipa clone although it gets it closer. So, it seems that beer smith defaults to tinseth but these recipes in zymurgy use rager. Any insight to this?

Click to expand...

That was going to be my suggestion and is usually the problem with discrepancies.  Unless the source states their formula for IBU, you won't know but trial and error with the different formulas will likely find the one they used.  You are never sure unless you ask the source.