Question on IBU levels

[rich]

Ok, so I just finished what was supposed to be an American Pale Ale with an IBU level of 30.
I used an equation from 'Designing Great Beers' that goes something along the lines of:

(Weight(oz) by Utilization% by AAU% by 7489) / (Volume gal by 1)

I boiled 1 oz Willamette hops for 60 minutes
1 oz Willamette at 30 minutes
.25 oz Columbus hops at 30 minutes
.25 oz Columbus at 15 minutes
1.50 oz Columbus for 2 minutes

Now when I do the calculations, I come up with an IBU of 80 (Jeese now it's an IPA).
However, I was then reading something along the lines of how hop additions after 30 minutes don't contribute any bittering, and so I am wondering if the calculations shouldn't be applied to hops after 30 minutes.
Also, I am curious if anyone has any easier methods, or good pointers. This is the first time I'm getting so much into the nuts and bolts of it. It lends to a greater sense of control, but I have to admit it's like chopping through a forest.
Anyway, any advice would be appreciated.


Thanks.

Rich

[Jughead]

Palmers www.howtobrew.com has a pretty good hop utilization chart based on boil time. According to it, hop additions after 30 minutes add bittering, just not as much.

I ran your list of hops through his calculations (using the software I wrote just for doing this kind of thing) and ended up with

Willamette - 5aau 60min = 20.7
Willamette - 5aau 30min = 15.9
Columbus - 15aau 30min = 11.9
Columbus - 15aau 15min = 7.7
Columbus - 15aau 2min = 0

for a total of 56.2

[GunNut76]

Rich- you can go to this page (http://hbd.org/cgi-bin/recipator/recipator) and plug in your recipe...you can screw around with stuff to make the beer what you want. Also do you use pellet or leaf hops? Do you use a hop bag? Those two things will affect the utilization.

[axis714]

thats my advice....as gunNut said i usually goto the spreadsheet ot the recipator and tinker with calculations works pretty good but i think sometimes the beer style calculator may be off a point or 2 here or there....but i still get a good general idea using it.

[rich]

Jughead,

I compared your calculations with mine and was about 2 points higher for each one (pretty close) but the last one (1.5 oz Columbus for 2 minutes) I didn't get zero. Acually, my calculation came out to 19.54 (a strong boost in IBU level).
Strange. Just curious, but how did your formula look. For this last one, my numbers were: (1.50 by .06 by .145 by 7489) / (5 by 1)

Guys,

Yeah, actually I used a liquid yeast for this batch, and the airlock has been chugging for 3 days now. I don't seem to remember fermentation times lasting that long with dry yeast. Has anyone else experienced this?

Anyway, thanks for all the feedback.

Rich

[Tweek]

lower temps will make your ferment go slower/last longer.