Error calculating partial boil IBU's

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Error calculating partial boil IBU's

Postby slothrob » Fri Sep 22, 2006 2:16 pm

I recently used v.20 to develop a partial mash/ partial boil IPA. I haven't done a partial boil for a while, and forgot to take into account the IBU maximum of 100. The result is that, in order to hit my target IBU of 63 in my final 5.5 gallon volume, I would have had to achieve 115 IBU in my 3 gallon boil. Since incorporation maxes out at 100 IBU, I ended up with a theoretical IBU of 100IBU*3Gal/5.5Gal=55.5 IBU.

Beertools Pro didn't take this into account when calculating my recipe. As a result my final IBU:GU will be closer to a hoppy APA's value of 0.9 than my IPA's target value of 1.1.

The program should consider this theoretical maximum IBU concentration when determining final IBU following a partial boil.

(Edited to add detail.)
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Postby slothrob » Wed Oct 11, 2006 3:25 pm

I was curious, was this question dealt with in a previous reply or is there something I'm missing that makes it a stupid suggestion?
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Theoretical Maximum

Postby jeff » Wed Oct 11, 2006 4:25 pm

slothrob wrote:I was curious, was this question dealt with in a previous reply or is there something I'm missing that makes it a stupid suggestion?


I'm not familiar with a theoretical maximum IBU, so BTP doesn't limit IBU based on a maximum concentration. Do you have reliable data proving these limits? Thanks.
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Postby slothrob » Wed Oct 11, 2006 4:31 pm

Only "common knowlege" and hearsay. It's often bandied about on the brewboard as the reason you can't make a big IPA from extract in a partial boil.

I'll see what I can find.
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Postby slothrob » Wed Oct 11, 2006 4:45 pm

I found this, so far, It's a bit confusing in that the utilization relationship to gravity is inverse, but ultimately more IBU's are possible at higher gravity. I'll look for something more scientific.

"Dennys Fine Consumptibles
01-09-2006, 05:01 PM
From http://www.allaboutbeer.com/features/246doubleIPA.html

I know I've seen a more formula based limit but this gives some input.

Brewers and consumers toss around IBU numbers that likely aren't accurate. "Hey, did you try the one that's 130 IBU?" we hear Thursday as we walk. In fact, that might not be possible. Brewing chemists can fill a blackboard explaining why, so Mitch Steele-an assistant brew master at Anheuser-Busch who also judged the category-provides an English translation:

"The maximum IBU level in a beer is somewhat dependent on composition of the beer. A higher alcohol, higher gravity beer can have more IBU than a beer at 5 percent alcohol. A 5 percent beer will max out at 120 parts per million iso-alpha acids, which corresponds to about 80 IBU. It is physically impossible to have more IBU than that in a 5 percent beer. As alcohol and unfermented carbohydrate in the beer increases, so does the ability of the beer to carry more IBU. Our hop research expert feels that the claim that some barley wines have over 100 IBU is probably valid."

What a chemist may measure and a drinker may taste can differ. "Perceived hop quality versus measurable bitterness, that's a tough one. I'm not sure there is a relationship because so much more is involved, like flavor balance, and the types of hops used," says Steele. "Many feel that low cohumulone hops produce a better, cleaner bitterness. I do know that during the judging, the imperial IPAs that were not harsh or unbalanced did better with the judges. Clean bitterness was key."

Of course to get higher alc you need high gravity which also limits IBU's."
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Thanks..

Postby jeff » Wed Oct 11, 2006 6:06 pm

Thanks for the info, keep me posted! :D
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Postby slothrob » Mon Oct 23, 2006 9:52 am

I just wanted to let you know that I was never able to find hard evidence for what these limits actually are. There was a lively discussion on the Brewboard where the experts seemed to acree that there was a limit somewhere between 90 and 120 IBU, but the published research seems sparse on the subject. The few published accounts that were dredged up were always in atypical brewing conditions and, while supporting that IBU limit window, could not be directly correlated to a normal brew session.

The dogma seems to come mostly from brewers anecdotes and personal experience, without the hard numbers you probably want before you tack this onto your program. Though many brewers are quite adamant about this limit.

Hopefully someone will do this experiment soon, though I suppose you could consider a check box burried in a hop menu somewhere that could turn on a 100 IBU limit as an option for brewers that want this to be taken into account.
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What I propose

Postby jeff » Mon Oct 23, 2006 10:16 am

I think that the limit can be included as a user defined preference. That way BTP is not rendered inaccurate upon new findings in this area. I will make a note of it for the next update. Thanks for looking into it!
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