IBU Calc issues

[kylefalhaber]

I brewed a Pliny the Elder clone a couple weeks ago and it is in the secondary now. It looks and smells great. I can't wait to give it a try in a couple of weeks! I am doing a little book keeping and I'm having trouble matching the IBU in the OP (IBU = 95). I changed the hops a little bit, but even with the original bill it doesn't seem to match. I am using the Tinsenth method as described in How to Brew by Palmer:

3.5 oz of Columbus (15% AA) = 52.5 AAU; Boil time of 90 and OG of 1.07 = utilization of 0.2062; Volume of 5 gallons; These give an IBU of 162.

0.75 oz of Columbus (15% AA) = 11.25 AAU; Boil time of 45 and OG of 1.07 = utilization of 0.1769; Volume of 5 gallons; These give an IBU of 30.

1oz of Simcoe (12.7% AA) = 12.7 AAU; Boil time of 30 and OG of 1.07 = utilization of 0.1481; Volume of 5 gallons; These give an IBU of 28.

Add these three together for a total IBU of 220. Does anyone know why/how I am so far off from the original OP? I don't know how he calculated the 95, but I think the 220 seems pretty high. Thanks!

 

[carton132]

I've read that Pliny clones will calculate around a theoretical 200 IBU, but will end up at around 90, 95 in reality. All I've seen were 200+ and I'll probably go with that when I try making it eventually.