Calculating Whirlpool into IBU

[caseyjones]

I'm curious how most of you calculate IBUs when it comes to a 20 minute whirlpool? Obviously, the wort is still very hot and utilization is still occurring.

When you are adding late additions for aroma, what thoughts go into the additional bitterness you will get from big knockout additions in an APA or IPA? Not that it makes a huge difference, but we're talking about a 10bbl system.

Thanks!

[jwalts]

I've thrown in my two cents on this issue in the past; here's a link to a similar thread with a link to another similar thread:

http://www.probrewer.com/vbulletin/showthread.php?t=21498

Recent samples that I've sent to a lab that have validated my general method, but there have been some huge exceptions. As James mentions, knowing your actual IBUs are very important. A hop with 10% alpha at harvest will probably have nowhere near that level ten months later. The section near the end of this article is a good primer on alpha acid losses over time, and the links include some detailed calculations:

http://www.brewingtechniques.com/library/backissues/issue2.1/garetz.html

That said, all the math in the world can't match the value of lab tests. Hopunion's Alpha Analytics (http://hopunion.com/10_AlphaAnalytics.cfm?p5=open) does great work for very reasonable prices on both beer and hops.

Joe
Ale Asylum
Madison, WI