Does the top-off water affect IBU?

[Elysium]

Here is an example: Let's say I brew a 1.062 beer but I want a bigger 1.053 batch....so I use boiled water to top it off...that's simple.
However....if the 1.062 beer has 45 IBU, will the final batch at 1.053 have the same IBU too? This is something that concerns me.

Any thoughts or ideas on this one?

 

[flars]

No, IBUs will be based on volume. If you dilute the beer, you dilute everything about the recipe.

 

[Cyclman]

It does in that the higher the gravity of the wort, the lower the isomerization of the hop acids, and hence bitterness.

So, putting hops into a 3G boil and topping off will be less bitter than a 5G boil with everything else kept the same.

It is probably not highly noticeable, but theoretically...