Hop isomerization

[Kushal]

I just calc'ed out some IBU's for our beers and I can't believe they are right. They seem much too low. We go light on the boil hops, but we add a ton of whirlpool hops. The whirlpool hops (and the boil hops) are sitting in the wort for around 55min (whirlpool and knock out time) at 210' to around 205' at end of knock out. Are we isomerizing at these near boiling temp's? If so is there any formula that could account for this?
Thanks

[Sulfur]

I'd use a 5% contribution on the isomerization rate in standard whirlpool usage (knockout, rest, and wort cooling).

[irishsnake]

Are we isomerizing at these near boiling temp's? If so is there any formula that could account for this?
Thanks

well, I would certainly think you would be isomerizing. Isomerization doesn't stop when you turn off the heat, unless somehow you magically cool your wort to fermentation temp all at once.

[gdebisschop]

If you're at 200+ for 55 min I think you're at very nearly full utilization (whatever that is for your system). The brewing company I used to work for took samples from all locations and tested for various things, bu's among them. Backing into the numbers drew us to the conclusion that even whirlpool hops were being utilized at our full rate (33%). At that time we were giving a lower % to whirl hops and everyone's actual bu's were high by the difference. I would recommend sending out some samples, getting some data and backing into your actual utilization.

Cheers,
Geoff

[Sulfur]

I mentioned the 5% because I remember reading it in a German journal some time ago. I guess it should be applied to German style beers with similar hopping regimens/schedules. I don't have any data/info on beers where significant IBU contributions are done in the last stages of the process and would be interested in hearing more. The best way would of course be to measure the effects independently.