# IBU Calculations Questions

Discussion in 'General Brewing Discussions' started by Brewer #49306, Oct 31, 2018.

1. ### Brewer #49306 New Member

Joined:
Apr 16, 2018
Messages:
27
16
Trophy Points:
3
#1
I was am brewing a recipe from a rather famous home brewers book and when I entered into my spreadsheet had a wildly different IBU result than the recipe called out. My next step was to enter it into the Brewer’s Friend IBU Calculator an the results were of course different again.

Book recipe
1.055 OG
7 gallon boil
6 gallons finished wort
1.8 ounces of 5% AA hops for 60 minutes
IBU 36

Brewer’s Friend
IBU 29.25

Mine
IBU 25.67

The difference between my calculations and Brewer’s Friend come down to utilization my U = .23 and Brewer’s Friend U = .26.

How would you get 36 IBU out of those hops? A U = .32.

Thanks for any insights.

2. ### J A Well-Known Member

Joined:
Jan 19, 2016
Messages:
3,476
2,694
Trophy Points:
113
Location:
Austin, Texas
#2
IBUs will depend on AA of the hops, gravity of the wort and time of exposure to boiling temp. Different calculators use equations that may assign different values here and there.
I'm not sure what some of your references are or exactly what your question is, but generally, you increase IBUs by increasing amount or AA of hops or time of boil. Wort gravity is inverse to hop uptake/IBU production.

Brewer #49306 likes this.
3. ### Nosybear Well-Known Member

Joined:
Jul 16, 2012
Messages:
9,400
6,643
Trophy Points:
113
Location:
Aurora, CO, USA
#3
Add to that the equation the author used to calculate the IBUs. Different formula, different result.

Brewer #49306 and J A like this.
4. ### Brewer #49306 New Member

Joined:
Apr 16, 2018
Messages:
27
16
Trophy Points:
3
#4
To be more clear all 3 recipes use the same OG 1.055and volumes 7 gallons preboil 6 gallons post boil and 1 60 minute addition of a 5% AA hop.
My sheet uses U = bigness * time factors.
For the time factor (1-e^(0.04*Time))/4.15
For bigness factor 1.65*0.00025^(gravityAvg - 1)

I am thinking of lowering the 4.15 to 3.6 since that would put me inline with the Brewer’s Friend calculator.

5. ### J A Well-Known Member

Joined:
Jan 19, 2016
Messages:
3,476
2,694
Trophy Points:
113
Location:
Austin, Texas
#5
I think you're getting off into the weeds. Just go by the BF recipe editor and brew beer. It's been working for a lot of us for a long time.

Brewer #49306 likes this.
6. ### Craigerrr Well-Known Member

Joined:
Mar 14, 2018
Messages:
4,701
6,903
Trophy Points:
113
#6
IBU's are pretty subjective, I would think that discerning the difference between the low to mid 30's might be tough to do.

Brewer #49306 likes this.
7. ### Nosybear Well-Known Member

Joined:
Jul 16, 2012
Messages:
9,400
6,643
Trophy Points:
113
Location:
Aurora, CO, USA
#7
Example, I did some recipe transcription last night. I'd get radically different results from the rather reputable source, Craft Beer and Brewing Magazine, particularly on late- and dry-hopped beers. I shifted the results to the Brewer's Friend calculator, it's always worked well for me with the default bitterness equation. As mentioned, bitterness is subjective and no one can taste a couple of IBUs either way. Based on individual circumstances of how I boil, when I'm given a recipe with an IBU range, I go with the upper end. That's the result of brewing a lot of beers and learning what I need to get from my hops. You'll get there but it will take time.

Brewer #49306 likes this.
8. ### Brewer #49306 New Member

Joined:
Apr 16, 2018
Messages:
27
16
Trophy Points:
3
#8
I changed my formula so it is more in line with Brewer’s Friend. I’ve used Brewer’s Friend for a few years now and like it. I just thought it was odd using that simple 1 hop addition at 60 minutes that the difference between Brewer’s Friend and the recipe was 7 IBU. Thanks for all the insights everyone.

9. ### Nosybear Well-Known Member

Joined:
Jul 16, 2012
Messages:
9,400
6,643
Trophy Points:
113
Location:
Aurora, CO, USA
#9
That's not much: I was getting results in the 80's when the original recipe was in the 20's.

Brewer #49306 likes this.
10. ### Brewer #49306 New Member

Joined:
Apr 16, 2018
Messages:
27
16
Trophy Points:
3
#10
Wow!

11. ### Nosybear Well-Known Member

Joined:
Jul 16, 2012
Messages:
9,400
6,643
Trophy Points:
113
Location:
Aurora, CO, USA
#11
Lots of late- and dry-hopping. Different calculators handle those wildly differently.