This is my 50th post here at FSB!
Doctor Bob Technical didn't confine himself to malt. No, he made a slide rule for hops as well. He called it the Hop-Go-Round.
Check out Alephenalia Publications, Seattle WA 98122. They don't seem to have a web presence, but we all know Dr. Bob is Randy Mosher, the man behind Radical Brewing. This is a great little device, and we'll see what it says for our new batch of brew.
For bittering, one ounce of Whole Organic Perle Hops (@ 8.1% α-acids), assuming a 25% efficiency in an hour-long boil, should yield 32 IBUs. The chart suggests less than 25% with a high-gravity wort, but I've always just bracketed readings for 20 and 25% to give me a ballpark figure. At 20% I get 25 IBUs.
I weighed out several half-ounce sets of the hops, and I think I'll have two or three flavoring additions. A half-ounce for 15 minutes is about 10-15% utilization. That gives us 6-9 IBUs. Another half-ounce for 5 minutes (5%) is 3 more IBUs. The total is 34-44. If the wort is not too big or sweet, that could be a nice match. We'll see what I do on brew day.
a.d. III Id. Aug