What about 90 min boils?

[Rkoory]

I have a double stout that I am planning, and was considering a 90 min boil to help get my gravity up, and potentially to get the most out of my hops. I believe that a longer boil time will increase the polymerization of the alpha acids, creating a greater bittering effect, but what else does this do? So I guess my inquiry has two parts

One, what impact will an 90 min boil have on my hops?

Two, any critiques of using various boiling times for your bittering hops?

 

[Beernik]

90 minutes is the most you want to go with hops. You'll get the bitterness but little hop character remains.

More than 90 minutes and you can get vegetal flavors. You also don't get much additional bitterness. The extra bitterness you get between a 60 and 90 minute boil really isn't that great.

 

[Rkoory]

Is there any more technical/robust information about the effects of boil time?

 

[fearwig]

You can always boil for thirty (60, whatever) for gravity and then add your 60 minute hops and start the timer. I have not noticed anything vegetal after boiling for 90 minutes, but if you got all your IBUs from a load of low-alpha hops, you might. Any IBU calculator will give you the calculation on bitterness between 60 and 90. It's like 5%.