IBUs in BYO Recipes Wrong?

I have the BYO Hop Lover`s Guide and have brewed up a couple of recipes. I noticed today that Ruination IPA recipe calls for a boil of 11 L diluted in the primary to 19 L. They claim IBUs of 100+ finished product, but obviously this is impossible. Even if a 100 were achieved at boil, it is then watered down to 50%, so the theoretical upper limit should be 50 IBUs, right?

This disturbed me out, so I started going through and running some of the math on all grain versions (to avoid the difficulty calculating changing gravity with late addition extract versions). Pretty much all of them came out way under the IBUs they are supposed to have. I am totally open to the fact that I may be doing something wrong, but I ran it through using the utilization formula in the guide, and then double checked with a calculator online (www. brew65.com).

Here's some examples:

Flying Dog Gonzo Clone:
9.7 g @ 16%AA x 90 min
30g @ 9%AA x 60 min
30g @ 9%AA x 30 min

By hand I got: 54.55 IBU for a full 19 l boil
The online calculator gave:
Tinseth: 53. 38
Rager: 49.05

This is a big difference!

The Yeti Clone is similar:
31g @ 13%AA x 60 min
16 g @ 13%AA x 30 min
14g @ 10.5%AA x 15 min
14g @10.5%AA x 5 min

This yields (by hand) 56.69 IBU
Online:
Tinseth: 56.55
Rager: 51.88

All are a far cry from the 75 IBUs the recipe claims.

I am really perplexed. Am I missing something? Help!

Jason

Just a thought before I think about it more... were you using a calculator that works in oz or grams? I just calculated out your first recipe and I got 108 IBU for a 5 gal (19 L) batch.

Also, when they give you the IBUs for a recipe, it doesn't matter that you are diluting it. They give it to you based on a full boil. If you are doing a smaller boil and then diluting, you should be coming up with (close to) the same IBU in the wort. There will be some difference based on utilization percent of your system and also decreased utilization because the gravity of the boiled amount is much higher. Higher gravity decreases hop utilization.

This has been noticed and discussed before in several places.

https://www.homebrewtalk.com/f14/confusing-byo-hop-calculations-2887/

And here!

http://www.beersmith.com/forum/index.php?topic=2984.0

Those discussions might help!

Revvy: thanks for the links. I find it absolutely bizarre that such different calculations could come off of different software. Weird.

BackBayBrewing: I forgot note OG (which is maybe why your calculation came in at 108). It was about 1.090 for both. And according to the recipes, IBUs should have come out at 75 for both. I have run this a few times, and also done it by hand using the formula and utilization schedule included in that same issue of BYO. I keep getting the same number: around 55 IBUs (depending on which recipe), which is the same as various online caculators give. I don't think my math is wrong.

I chose all grain recipes to avoid any difference that might occur with using late extract or dilution. 25 IBUs seems like a heck of a lot to be off. I really find this disturbing.

It is especially weird with the Ruination IPA: the recipe specifically calls for a 50% dilution from an 11 L boil, AND claims to yield 100+ IBUs. This is impossible, as the max IBUs you can achieve are 100-120, so a 50% dilution the end result would have to be less than 60 IBU.

Am I missing something?