Originally Posted by scottab
So the final result should be balanced to the style regardless of what beersmith or android brewer app says and the mfg ibu is correct?
It used to be believed that IBUs were impacted by wort gravity, and it's since been disproven. If you boil a given amount of hops in a given amount of solution, the IBUs will not change based on the gravity of the wort. The calculators haven't taken this into consideration- and I"m not sure they ever will as I don't think it's an easy fix in the software.
The only thing I know of that does impact hops utilization in a partial boil is the fact that the beer is "topped off". That's not an issue for a beer like yours, but in a huge IPA where you want to have a ton of IBUs- say, 80, it may be an issue since there is a maximum of hops oils that can be isomerized in liquid. That is generally thought to be around 100 IBUs. So, taking a 100 IBU wort and adding a 0 IBU water addition would mean a reduction in the IBUs. If you had 100 IBUs in 2.5 gallons, and then topped off with 2.5 gallons of water (0 IBUs) then the IBUs would be 50 at most.
That has nothing to do with wort gravity, though- that's just the nature of hops oils and isomerization.
In most beers, this isn't at all a concern and it's the software that is giving you such a low IBU guestimate.