IBU Contributions from Flameout and Hopstand Additions

So after devouring my last IPA based on Braufessor's excellent Northeast IPA, I've decided to make another attempt for a friend's wedding. My first attempt at the recipe is probably a little too bitter for most palates, so I'm going to make a few modifications to cut down on the IBUs. Which brings me to the issue at hand...

How do you estimate IBU contributions from flameout and hopstand additions? I understand that as the temperature plummets the degree to which isomerization occurs is somewhat limited. Where does that limit occur? The IBU calculator in BeerSmith seems to over estimate hopstand bittering. So where / how do you estimate a more accurate value?

I appreciate any feedback. Thanks!

This article has some of the info you're looking for: http://byo.com/component/k2/item/2808-hop-stands
As one data point, I do my hop stands starting at 190F and ending at about 180F for 30 minutes. I've found it gives me the same utilization as a 10 minute boil (based on Tinseth).

I've always read that the point at which you stop extracting bitterness is around 170 degrees F. So, if you want the most control, just use boil additions to achieve your desired bitterness, then chill quickly to 170, turn off your chiller and then do your hop stand. That would give you the ability to get a lot of hop flavor and aroma from the hop stand, but still have a lot of control over your IBUs. Just my take on it. I've done just that and it seems to work out for my taste.

That being said, most of the styles that people are doing these huge hop stands for are styles that are going to approach or exceed the threshold at which we can't perceive any more bitterness. So I imagine it's pretty tough to overdo in reality if you're going for one of those styles.

I chill quickly with the plate chiller down to 162F and then add all my whirlpool additions. I then keep it between 162-172F. After the whilrpool I chill to pitch temperature.

The key points are;

- fast chill to whirlpool and a fast chill to pitch in doing so maintain hop aroma and get a good cold break.
- keep the wort above 162F to maintain pasteurization
- keep the wort below 180F to prevent the formation DSMO
- Keep the wort below 180F as hop utilization is close to 0%

This way I get no hop bitterness from whirlpool addtions.