Brewing BCS Janet\'s Brown tomorrow

bazookazilla

I went to LHBS today and got ingredients to brew Janet's brown tomorrow.  I wasn't paying attention at the time but I got 3 ounces of Northern Brewer hops at 9.8% AA.  The recipe calls for (in different additions, 3 oz)  6.5% AA.  I understand how homebrew bittering units work, but I don't understand how to calculate IBUs.  Is there a simple formula that I can use?  Sorry to make it urgent, but my starter started rolling about 9 hours ago."The word unblowupable is tossed around a lot these days..."
Homer Simpson

BDawg

W = weight in oz
AA = Alpha Acid Percent (ie, 4% means use 0.04)
UTIL = Utilization - 60 mins -> .28, 15 mins -> .08, -0 mins - 0
V = volume in gallons
For FWH, use .10 (same as 20 min addition)
IBUs == Sum of (W * AA * UTIL * 7462) / (V * (1+GA))
If Gravity > 1.050
GA = (BOIL_GRAVITY - 1.050)
----------------------
0.2
otherwise,
GA = 0
Examples:
5 gallons 1.050 Weizen wort
1 oz 4% Hallertaur at 60 mins
GA = (1.050 – 1.050)/0.2 = 0
(1 * .04 * .28 * 7462) / (5) == 16.71 IBUs Total
5 gallons 1.065 IPA wort
1oz Cascade @60
2 oz [email protected]
2 oz [email protected]
GA = (1.065 – 1.050)/0.2 = .075
(1 * .08 * .28 * 7462) / (5 * 1.075) = 31.09
(2 * .08 * .08 * 7462) / ( 5 * 1.075) = 17.76 ==
31.09 + 17.76 = 48.85 IBUs total
Hope this helps-B'Dawg
BJCP GM3 Judge & Mead
"Lunch Meat.  It's an acquired taste....."  -- Mylo

bazookazilla

it does,thank you muchos"The word unblowupable is tossed around a lot these days..."
Homer Simpson

brewinhard

This is exactly why I use BeerSmith. My head hurts.  

2xw10nvcr1g.png

"Mash, I made you my bitch!" -Tasty

brewinhard

+1 for computers...."A bad man is a good man's job, while a good man is a bad man's teacher."