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Old 12-08-2008, 01:52 AM   #1
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Default How do I calculate actual IBUs?

I do partial boil extract recipes and I'm trying to figure out how to make an IPA with a lot of hops. I've read a lot of the other threads on partial boils and maximum IBUs, and I have a good grasp on how high you can go.

I have been playing around with Beersmith, and the IBU calculator is obviously a bit odd. It lets you add hops and never stops increasing the IBUs. I got some good info from this thread:

but without going into a lot of math and averaging Tinseth estimation with other estimations, etc. etc., here's what I was thinking:

What about just adding hops to my Beersmith recipe until it shows 100 IBUs, and then do some easy math those IBUs with the 0 IBUs from the top off water.

For example: 3.5 gal boil with 100 IBUs, 1.5 gal top-off water (0 IBUs) would make a batch with 70 IBUs. (3.5*100 + 1.5*0)/5

Is this close enough, or am I missing something about Beersmith?

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Old 12-08-2008, 03:02 AM   #2
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You've got it right. A somewhat simpler equation and the one I use is, (Vb/Vt)*IBU where Vb is boil volume, Vt is total batch volume and IBU is the IBUs BeerSmith calculates for you.
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Old 12-09-2008, 02:33 AM   #3
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If you want some extra math, try the calculation at the very bottom of this page. It might be a way to doublecheck BeerSmith.

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OOPS, sorry its not the bottom, its kind of in the middle. You'll see it, its a section titled IBU.
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