So I've been wanting to brew a Pliny the Elder clone for quite some time now. I found the recipe in the most recent issue of Zymurgy which is a repost from the 2009 recipe from Zymurgy. (https://www.homebrewersassociation.org/attachments/0000/6351/doubleIPA.pdf) My question is that I entered the exact recipe from the article into Brewers Friend and I get a whopping 259 IBU's in a 5 gallon batch!! However the recipe states that the beer ends up only being 90-95 IBU's (actual). How can there be this much variance from the recipe and what I get in Brewers Friend? The culprit is certainly the 3.5oz Columbus addition at 90 minutes. My thought is perhaps there is there a maximum IBU extraction percentage that's throwing off the formula? Could bitterness extraction ramp down as the boil continues? I.e. if I add 1oz of hops with a 3 hour boil will it continue to add bitterness? I'm assuming there is a maximum you could extract from 1oz of hops regardless of the boil length. It seems that my beers are never as bitter as the commercial examples even though my bitterness in Brewers Friend matches the commercial stats. I understand that estimating IBU's is not an exact science, but maybe there should be some buffers added (age of hops, length of boil, etc.) that more accurately represent what a homebrewer gains from our non-pro-brewer quality hops?