# IBU calculation question

Discussion in 'Recipe Editor' started by Fatty G, Oct 12, 2018.

1. ### Fatty G New Member

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#1
Hi team, apologies if this has been asked a million times before (I did skim through but couldn't quite find this). Maybe it's obvious to everyone else, but my question is hard to define, but here I go.

When I brew, I set the batch size to the 'fermentor volume' which is the amount I end up with in the fermentor. However, I always chuck everything in, I don't whirlpool or anything. Of course, my ending volume (the volume I actually bottle) once trub has settled is considerably less. For instance, this is my last recipe:

So, batch size was set to 12L because that's how much went in the fermentor, but I ended up only bottling 9.25L (yes, that's a lot of trub for such a volume, I can't quite understand it either!). Anyway, my question is - am I right in thinking that the IBU rating is based on the batch size of 12L, and therefore the actual IBU rating will be much higher due to the lower volume actually bottled?

Thanks!

Matt

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2. ### Mark D Pirate Well-Known Member

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#2
Your boil volume and boil gravity are what determines how much bitterness you get from your hops .
Test it for yourself and change the boil volume setting in your recipe

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3. ### Fatty G New Member

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#3
Yes, but surely the final volume of actual beer is a part of that equation. The volume I've given the calculator is 12L, but I actually ended up with 9L of beer. Presumably the calculation of 37 IBU's above is based on 12L, not 9L? I'm starting to think I've gone mad here...

4. ### Mark D Pirate Well-Known Member

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#4
No , you might be mad and that's OK.
I'd be using actual liquid volume in ferment vessel as target .
How is it your batch size is larger than boil volume?

5. ### Fatty G New Member

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#5
Thanks Mike, but when you say 'actual liquid volume inside fermentor', for me that includes all of the trub, hops etc which are not liquid...so are you saying use that volume i.e. 12L in my example above?

6. ### Mark D Pirate Well-Known Member

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#6
Mike? What the bloody hell!!!! Only 1 letters are the same ya drongo .
I've been called worse by better men grrrr.
( translated version)
Sorry my friend but my name isn't actually Mike , I can understand the confusion but I'm actually a Mark.
( cannot translate next bit but slightly offended in fluent Aussie)
Hope you are well, please try harder

7. ### Head First Well-Known Member

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#7
You can't have a fermenter volume larger than boil volume unless you add water after a partial boil. You can't have a lower OG than boil gravity unless you are adding water after a partial boil. To answer your question I would suggest you go into the frequently asked questions and do some reading. That will help you understand more than Mike and me. (Sorry Mr. Pirate, couldn't resist) Is your question how does a partial boil affect IBU ? If so that is addressed in FAQ section.

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