Here's some excerpts from Mike "Tasty" McDole's Facebook feed from earlier this month, I don't think he'd mind. I think he might even be looking for others to help experiment from the sounds of it:
Mike: Today I'm trying to unravel the mystery of hop utilization in the whirlpool. I could use some help.
I was thinking the challenge here is to develop a formula based on the alpha acid level, volume, temperature, and time. I could just make one batch of minimally hopped wort and whirlpool small amounts, collecting samples over 30 minute period for a given alpha at a given temperature. I'm looking for some help a brewery that has their own equipment for determining IBU levels.
Mitch Steele (Stone Brewing): 18% of our wort bitterness in Stone Ruination IPA comes from the whirlpool addition. I'll have to do the calculation to see what that is in terms of efficiency.
Mike: That's great info Mitch. That's what I'm looking for here. Matt says he gets 22%. (I'm assuming he's talking about Matt Brynildson/Firestone Walker)
Mitch: 18% is the percentage of total IBU's we get. We dump a lot of hops in the whirlpool, so I need to calculate the actual utilization. Our whirlpool is 15 minute fill, 15 minute rest and 45 minute KO-total 75 minutes
OK, I did the calc, it looks like 9.6% utilization with our hops that are added prior to filling the whirlpool, 75 minute residence time at ~200dF, added to 18dP wort.
Jim Matt: At Sun King, for our Osiris Pale Ale, (according to our magic spreadsheet) it looks like we are ~10% utilization for a 20 minute whirlpool and a 60 minute knockout, on a 30 BBL batch.
Colin Kaminski: Mitch, do you calculate the amount of IBUs stripped by the yeast and does that effect your pitching rates?
Mitch Steele: No we don't. We can measure IBU, so we measure wort IBU and beer IBU, and adjust hopping rates if beer IBU drifts. Of course, pitch rates need to be consistent! I tried to talk the A-B R&D dept. into doing a similar study, but couldn't get the proposal through, given that we weren't maximizing hop usage or brewing really high gravity beers. However, what I do know about this came from the work we did get done at A-B. I think Tom Shellhammer up in Oregon might be looking at this too.