# Boil Size effect on IBU

Discussion in 'Recipe Editor' started by DanaPellerin, May 29, 2017.

Tags:
1. ### DanaPellerin New Member

Joined:
Apr 18, 2016
Messages:
21
18
Trophy Points:
3
Gender:
Male
Occupation:
Web Developer
Location:
Fresno, CA
#1
I have an extract recipe and currently the boil size is set to 3 gallons, and the resulting IBU calculation is about 70 IBU. I was thinking about doing a full boil of about 7 gallons, but changing that parameter increases the IBU to 120.

Can somebody explain why boiling more water (with no other changes) would nearly double the resulting IBU?

Thanks

Dana

-->
2. ### jmcnamara Well-Known Member

Joined:
Aug 29, 2012
Messages:
2,420
1,918
Trophy Points:
113
Gender:
Male
Location:
Rosedale, MD
#2
Hop extraction is inhibited with a higher gravity boil.
You still have the same amount of sugars there but you're increasing the volume over twofold. So your hop utilization is better
I'm sure there's more science to it but that's the simple version

-->
3. ### DanaPellerin New Member

Joined:
Apr 18, 2016
Messages:
21
18
Trophy Points:
3
Gender:
Male
Occupation:
Web Developer
Location:
Fresno, CA
#3
Last edited: May 29, 2017
Interesting. Thank you!

However, I think there's a shortcoming in the software if you add only part of the extract to the smaller boil to keep the gravity correct. Hmmm....

4. ### Yooper Administrator Staff Member

Joined:
Nov 16, 2013
Messages:
2,681
1,881
Trophy Points:
113
Gender:
Female
Occupation:
Happily retired
Location:
Upper Michigan/Florida
#4
There are a couple of things in play here. First, hops oils are limiting in solubility, and in isomerizing once the wort is saturated. That means that no matter how many hops you add to the wort, you're limited to under 100 IBUs or so just because of that principle. So the calculator may come up with 120, but it's simply a calculated number and not showing the very real ceiling of 100 IBUs. Actually, some of the hoppiest beers have been measured in actuality at 80 IBUs, even when calculated to 200+, such as Pliny the Elder. That's because of this solubility/hops oils saturation.

Also, when you do a partial boil of the wort, you are diluting the IBUs. Here's why. Say you did a boil of 2.5 gallons, using plenty of bittering hops and got an IBU of 100. Then you add 2.5 gallons of water at the end (with 0 IBUs). That means your five gallon batch has 50 IBUs at a max. That's the limitation of a partial boil.

It does help adding the bulk of the extract late in the boil- due to the wort gravity/hops oil isomerization issue but even so you'll never get the same IBUs as a full boil would, due to that dilution issue.

Adding the bulk of the extract late is one way to maximize the IBUs you'll get, though, and that should be done for that reason, as well as for better taste in the final beer (so you don't get that "cooked extract" taste that is present in some homebrews).

DanaPellerin and Trialben like this.
5. ### Ozarks Mountain Brew Moderator Staff Member

Joined:
Nov 20, 2012
Messages:
7,474
3,630
Trophy Points:
113
Gender:
Male
Occupation:
IT Managment
Location:
The Ozark Mountains of Missouri
#5
Ive found the simplest way to brew a partial is just double your hops, when adding water later it cuts all flavor in half even hop taste

-->