Calculating IBUs using Trub loss

Keith_G

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Hi.  I'm confused and hope someone can enlighten me....

My recipe starts with 7.5 Gal of water, 1.25G boil off and 1.0 Gal Trub Loss, so I end up with 5 Gal in the fermenter (6 Gal in the kettle considering the 1 Gal of Trub).  Beersmith says the IBUs are 34.7.

Same recipe, change trub loss to zero, so it appears I have 6 gal going into the fermenter (still 6 gal in the kettle)...  Now Beersmith says the IBUs are 37.6.

I would think the IBUs would be the same either way since there is 6 gal left in the kettle at the end of the boil in both cases.....

Thank You!
 
I'm not getting the same variation that you are, but I do see a lowering of utilization.

I don't know the exact calculations used in BeerSmith, but there are published papers showing that kettle proteins absorb alpha acids very effectively. Larger protein levels = lower hop utilization.

That might not be exactly what's being predicted here, but it's close, even if unintentional.

 
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