Hops IBUs, how does it work?

[Griffsta]

If i have a recipe that calls for, lets say, Cascade at 5.5, but I can only get Cascade with 7.8, then how do I work this out in my recipe?

For example, my recipe (beersmith) suggests 34 IBUs, but if I plug in the same weight of the cascade that I have, then I end up with 54.

How do I resolve this?

if I cut my hops in half for each addition, I end up at about 34, but how do I know if I am taking the hops out of the right addtion (either bittering, aroma, etc.)

Thanks

 

[Thumper]

I am too new at this to help you for sure, but my inital reaction is to reduce to amout of the bittering hops. I believe that this is where the majority of the bittering is coming from.

I an intrested in this question as well. Please wait for some more seasoned brewers to answer for sure.

Cheers,

 

[ifishsum]

Don't cut each addition in half - if you want to keep close to the original IBUs of the recipe I would reduce only your 60 minute addition by maybe 20%. Anything additions at less than 30 minutes won't significantly affect IBUs so don't reduce - even though the recipe calculators will change the IBU value somewhat it's more flavor than bitterness. You don't want to give up flavor by reducing the later additions. Myself I usually don't change much of anything for a small variation in AA%, but then I don't mind a few extra IBUs either.

If you post your full hops schedule we could help a little better.

 

[Ysgard]

If i have a recipe that calls for, lets say, Cascade at 5.5, but I can only get Cascade with 7.8, then how do I work this out in my recipe?

For example, my recipe (beersmith) suggests 34 IBUs, but if I plug in the same weight of the cascade that I have, then I end up with 54.

How do I resolve this?

if I cut my hops in half for each addition, I end up at about 34, but how do I know if I am taking the hops out of the right addtion (either bittering, aroma, etc.)

Thanks

For bittering additions (>=45 minutes) you multiply the recipe's addition by the recipe's AA divided by the actual AA.

In this case, 1oz (5.5/7.8) = .705. I would not cut your later additions by much if at all. Alpha acid is not what you are getting out of the late additions.