Dry hopping's effect on IBU

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Well-Known Member
Apr 24, 2007
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Livonia, MI
I don't know if there is an easy question to answer, but if anybody can, I know i'm in the right place.

Does dry hopping have an effect on IBU's?
If so, how do you calculate?

I've got a stone ruination clone in the primary now, and its going to get 1/2 oz. of centennial in the secondary. The IBU according to Promash is at 89.7, but it dosn't really let me put in anything for dry hoppinng.
The other guys have answered your question already, but just for you own reference regarding promash: set the boil time for your hops addition to -1 to have it as a dry hop addition. Likewise set the boil time to anything greater than the batch boil time to have a first wort hop addition.
The oils and resins in hops that create bitterness are not readily soluble in wort. They need to be isomerized, and that happens in the boil. So, to answer your questions, dry hopping should have no effect on the IBU's.

However, I personally believe that it adds to the perception of more bitterness. If you take a beer with the exact same grain bill, and the exact same hop schedule, and then you dry hop one of them, I think the dry hopped beer is going to taste more bitter.
Its important to remember that IBU/bitterness is not the same as 'flavor' when speaking of hops.
bitterness is a taste or aspect of a flavor, but is only a partial component.

I think cubbies comment about 'perceived bitterness' is very valid, since the aroma of the hops along with the flavor may cause one to taste more of the bitterness already present...emphasize it. this can be helpful when a beer finishes too sweet and has an imbalance between malt sweetness and hop bitterness. you can 'trick' the drinker if they don't have the palete of a bjcp judge :)