Hop Ibu question.

[Stubby]

I was wondering if lets say I am Brewing a Imperial Russian Stout or another big beer and you hit your Pre Boil OG. And go ahead and stick to your normal Hop addition. But Then you realize that you haven't gotten close enough to your final gravity. My question is If I have my Hops in a hop bag and I remove them from the boil will my IBU's still continue to increase If I need to boil longer to get the correct Final gravity?? I have ran across the problem a few times, just curious if anyone knows for sure?
Thanks

[schooly]

I would venture to guess that depending on how long that bag of hops has been in the boil you have already imparted IBU's and those will continue to add bitterness, the question is how much. If it's a big beer like an RIS, what about adding more fermentables instead of boiling longer (like DME)? Or use Pro Mash to determine how long the hops were in and what bitterness they contributed?

[mwedge]

If you remove the bag of hops then IBU's should not increase. No more acids can be isomerized since the hops have been removed.

[Mr.C]

But how quickly are the acids isomerized? If there are still un-isomerized acids in the wort when you take out the hops, then they will continue to isomerize and add IBUs. I just don't know how long it takes. Either way, can we really perceive a difference of a few IBUs in a RIS?

A secondary question...Which formula do you guys prefer in your brewing software for calculating IBUs? I've always been curious, because when someone tells you to shoot for XX IBUs in their recipe, the amount of hops that the software tells you to use can vary drastically depending on formula used (as well as other parameters like evaporation loss, efficiency, etc).

I've seen more than 10 IBUs difference between various brewing software or formulas, using the same amount of hops. In one particular case, the two IBU values I received were 21 and 35. Sorry, but there shouldn't be that big of a difference between formulas. I know they are just an estimation, but still...

[Stubby]

Well Also the depending on the age the AA can change. No telling how old some of these hops are at some of your LHBS.So really its a crap-shoot to get it exactly. I assume we just use these as home brewers to have some what of a consistency.

I thought of adding DME Brian. But I think that might change the complexity of a Russian Imperial stout. (Body, Roast Etc.) Most of the things I have read is to boil off half the volume of the wort.

I did a 2 hour boil on mine and started with 14 gallons, After the first hour I added a bittering hop. I was then going to have one additional hop addition at the end. Well at the end, I took a gravity reading and still needed to boil off some more to get my finial gravity reading I was shooting for. So I pulled out the hop bag and continued to boil for another 30 mins or so. So I guess the question I had was that additional 30 min boil gonna make me greatly overshoot my IBU mark.

[mwedge]

no you should not overshoot your ibu mark. i would bet that almost all homebrew is actually under the ibu levels that you think you are at. back in the day when my dad worked at miller they ran a few of my homebrews through their lab and gave me all the details (abv, ibu, srm, etc) on the beers. all of them were about 8-10 ibu lower than the calculations, which i believe i was using the "Rager" method.

[kking]

The worse case is the RIS will take more celler time until the hop character is what you want. Mine had "150" calculated ibu's and was perfect after a 12 months.