Vastly different IBU calcs from different calculators?

[zapbryann]

Hi all,

Was trying to calculate my IBUs from the following recipe using 2 different online calcs.

3 gal partial boil
5 gal total
1oz of Nugget 12.4%AA @ 60 min
.5 oz of Centennial 9.9% AA @ 30min
.5 oz of Centennial 9.9 AA @ 18min
1oz of Williamette Dry Hops 4% AA (which I assume I add as a 0 min boil time.)
All hops were pellets
OG was 1.060

Using this calc ( http://www.brewersfriend.com/ibu-calculator/ ) I get total IBUs at 46.07

Using another calc ( http://www.rooftopbrew.net/ibu.php , using Ragers equation, 5 gal batch size) I get IBUs at 80.6

Which should I believe?

 

[BobC]

My Promash calculator came up with 81.7 for pellet hops and 74.3 for whole hops. So I would go with the rooftopbrew of 80.6. Since dry hopping doesn't add any bitterness the Williamette hops will have no effect on the IBUs.

 

[ArcaneXor]

Depends on which formula you use. The difference between them is normal. Use one, and stick with it.

 

[prrriiide]

There's a good discussion on the subject here.

Different scales produce different results. Also, make sure that the batch sizes are identical as you compare.

 

[nebben]

Tinseth or Rager. Each formula will give you the different numbers which you might be getting.

 

[Dr. Francois]

Depends on which formula you use. The difference between them is normal. Use one, and stick with it.

I agree...pick one formula and taste the beer. Before long, you will know what 40 IBUs in a 1.050 beer taste like.

I have a similar setup to you, OP (20 qt pot partial boil). I use Tinseth, mostly because Yooper does and I like Yooper.

Besides, I wouldn't be surprised if our understanding of IBUs and extraction changed significantly in the next few years. I remember hearing a brewer talking about a beer in which ALL of the hops were added at flameout (a process that would barely tip the scales on most formulas). He sent the finished beer to a lab for testing, and it had a very high figure for measurable IBUs. I don't recall exact numbers, but it was something like 20 expected and 70 measured.

Thus, I think we should use hops the way we use cooking herbs: instinct and experience.