Issues with IBU Values in 'Brewing Classic Styles'

[Netflyer]

Has anyone who has used recipes from 'Brewing Classic Styles' (Palmer, Zainasheff) noticed the IBU's given seem high? Maybe it is just my beersmith program but I know when I enter a recipe from one of our members and most any other recipe beersmith nails the IBU's (as it should) So I'm attempting to brew a recipe from BCS's and it calls for:

6 gallon batch - 2 oz EKG 5%AA for 60 min. When I put that into beersmith I get 31.8 for a 6 gal batch, 7.5 gal boil. The BCS recipe states 41 IBU. Another recipe with 1.5 oz of the same EKG 5% states 29 and for me beersmith states 23.8.

All recipes in BCS are for 6 gallon batches.

Anyone know why the IBU values stated in the recipes would be more than 20% higher than normal?

Thanks!

 

[Bokonon]

I don't have my BCS handy but I ran the numbers in beersmith just using the bitterness calculator.

Using 1.050 as estimated OG I came up with your number.

Switching to rager IBU formula (tinseth is default) and pellet hops I get 41 IBUs

 

[SumnerH]

I don't have my BCS handy but I ran the numbers in beersmith just using the bitterness calculator.

Using 1.050 as estimated OG I came up with your number.

Switching to rager IBU formula (tinseth is default) and pellet hops I get 41 IBUs

That's exactly what's going on. Different formulas for estimating IBUs can vary pretty widely. The important thing is to pick a formula and stick with it, so that you have a regular measure against which to make adjustments. Just don't assume that any of them are all that accurate (within 30% is pretty good for most formulas, and it's not uncommon to be way outside that range for anything even slightly odd--recipes with wheat, rye, or simple sugars, or odd hopping schedules, or partial boils, or whatever).

Rager, Mosher, and Tinseth are probably your best bets (I like Tinseth, myself); BBR did some measurements comparing estimates between various formulas, and those 3 had the fewest times they were way off.

But things can vary hugely--there were certainly recipes where all of the above estimated twice the actual IBUs, and there were some recipes where one formula estimated 18 IBUs and another estimated 74!

 

[yodalegomaster]

Jamile uses only Rager formula, because that's what he knows. the Tinseth is probably, the closet to fitting the whole curve. The moral to the story is pick one and learn it stay with it, list it when you refer to IBU's in recipes.

 

[Netflyer]

But things can vary hugely--there were certainly recipes where all of the above estimated twice the actual IBUs, and there were some recipes where one formula estimated 18 IBUs and another estimated 74!

Yes, to say nothing of the actual AA of the hops you are using varying/degrading.

I didn't think about the different hop estimation methods. That they could differ by over 20% almost means they are rejecting the IBU scale. I mean with that variance each is creating their own re-calibrated scale right? IBU becomes a much cloudier attribute like this. I suppose it is best to say, 'Use 2oz of x hops at y alpha for this recipe' and just leave it at that w/out stating the IBU.

 

[david_42]

The "curves" in the calculators are equations that approximate the empirical data. Some better than others. There is also the problem that the different alpha acids isomerize at different rates, which means IBUs are dependent on humulone/cohumulone/adhumulone ratios. None of the calculators take this into account, but if you look at the 60 minute points, you can see there is a fair difference.

 

[SumnerH]

The "curves" in the calculators are equations that approximate the empirical data. Some better than others. There is also the problem that the different alpha acids isomerize at different rates, which means IBUs are dependent on humulone/cohumulone/adhumulone ratios.

They also ignore oxidized beta acids, which contribute to true IBUs. That means most high-alpha varieties (which have higher alpha:beta ratios) are going to have their IBU contributions somewhat overestimated by all the homebrew formulae.

 

[david_42]

Good point, and as hops age the oxidized beta acids become more important.