Strange value for Tinseth IBU from hobbyBrew

[MarcoS82]

Hi guys, I want to brew the IPA meantime recipe from this link:

http://www.brewersfriend.com/homebrew/recipe/view/6425/meantime-ipa-clone

I'm using HobbyBrew to calculate the amount of hops, but I obtain a tinseth IBU that is very different from the recipe (82,4 vs 36.61).
I attached the screenshot from the HobbyBrew calculation.


Where is the problem? maybe the hops at "first worth" where boiling time is set to 75 minutes?

 

[cladinshadows]

You're almost certainly right. Many people (myself included) calculate the IBU contribution of first wort hopping as equivalent to boiling for 20 minutes (even though they are in there for the entire boil), not 75 minutes. That's fairly common, so it's probably also what Brewer's Friend uses.

Try out the 20 minute concept and see if that gets you closer. If not, you can calculate your required hop quantity by matching the AAU's with the source recipe. AAU's are "Alpha Acid Units" and you can calculate them by multiplying the hop amount times the alpha acid content of your hops.

Example: the source recipe has 40 grams of East Kent Goldings at 5.6% alpha acid. Let's say you can only get East Kent Goldings with an alpha acid content of 4% AA. You would need (40 * 5.6) / 4 = 56 grams of East Kent Goldings to achieve the same IBU contribution.

Hope this helps.