I followed the recipe since I’ve never brewed this one before. Zymurgy, July/August 2007.
The recipe says 92 IBUs, but Beersmith calcs something like 28. The warm and uncarbonated sample I had last night did not taste nearly hoppy enough to be close to Old Rasputin.
The recipe calls for 2 oz of Cluster for 60 minutes, 1 oz of Northern Brewer at 2 minutes, and 1 oz of Centennial at 2 minutes. I’ve seen a couple other recipes (BYO) that take the Cluster up to nearly 4 oz, but even then I’m not getting 92 IBUs.
I’ve never been a numbers guy so I don’t usually pay all that much attention to IBUs. And I know Beersmith is only a tool. But what am I missing here?
I actually used a recipe from Zymurgy that is pretty much identical, but all-grain and uses fewer Cluster hops. I adjusted the recipe only to replace some of the base grain with DME.
A lot of times these clone recipes just scale the brewery’s recipe as-is. If the brewery uses a whirlpool or has something else in their process that would increase their utilization that would lead to some discrepancy compared to the homebrew scale.
I calculate about 58 IBUs for 5 gallons, assuming the Cluster alpha at about 7%, Northern Brewer at 9%, and Centennial at 10.5%. Here’s how I swag it, for 5 gallons – it’s all about memorizing the magic factors at the beginning:
3.6 * oz * AA% = IBUs from bittering additions @60 minutes
1.6 * oz * AA% = IBUs from flavor additions @10-15 minutes
0.6 * oz * AA% = IBUs from aroma additions @5 minutes
Add all these together, then add about another +1.5 to the final total and round everything up.
So I get about 50.5 + 3 + 3 + 1.5 = 58 IBUs. Nowhere near the 90s, like you said.
+1. I’ve noticed it a lot. What I do with clones where the IBUs obviously include a lot of whirpool hopping (because the numbers don’t add up in software) is to take the given IBU number, add the amount of late hops I think I need to emulate the beer, and add the balance of the needed IBUs in the bittering addition. It comes out closer to the intended than trying to second guess whirlpooling amounts and methods.
May be a dumb question, but are you properly taking batch size into account? 48 sounds pretty close to half the ibus (then with a Rager gravity adjustment). Did you plug 5 gallons worth of hops into a 10 gallon recipe?
The brewery says Old Rasputin is 75ibu. They probably whirlpool above 190F for 60 minutes after flameout which extracts more ibu than you calculated. If you don’t want to whirlpool for an hour, you can add more hops to get closer 75ibu and start chilling at flameout. Ibu are still accumulating after flameout depending on the rate of your method of chilling.
I still am convinced that brewery-released recipes are usually scaled accurately for the malt bill, but as for hop schedule, the IBU number sometimes doesn’t appear to add up in software because the brewery gets considerable IBUs from whirlpooling. If you have the stated total you can at least get in the ballpark.